What kind of computers are there is an eternal question of the younger generation.
There are two main types of computers: analog and digital.
They differ in the principle of construction, the way of internal presentation of information and the response to commands.
Analog computers
An analog computer is a machine that performs arithmetic calculations on numbers represented by physical units.
For example, in mechanical analog computers, numbers are represented by the number of times the gears of a mechanism turn.
Electrical analog machines use voltage differences to represent numbers.
An essential characteristic of analog computers is that the quantities representing digital data are constantly changing over time.
Therefore, analog computers are different from more common digital computers, which operate only with numbers, or quantities, in step changes.
Analog computers are mostly mechanical or electrical machines that can perform addition, subtraction, multiplication, and division operations.
The output of such computers can be expressed in the form of graphs drawn on an oscilloscope screen or on paper, or an electrical signal used to control a process or the operation of a mechanism.
These computers are ideally suited for automatic control of production processes, as they instantly respond to any changes in the input information.
They are also used in scientific research, especially in those areas of science where cheap electrical or mechanical devices can simulate the situations being studied.
In some cases, using analog computers, it is possible to solve problems without worrying about the accuracy of calculations than when writing a program for a digital computer.
For example, for electronic analog computers, problems requiring the solution of differential equations, integration or differentiation can be easily implemented.
An automobile transmission is an example of an analog computer program that changes when the gear shift knob is moved, causing the fluid in the hydraulic drive to change the direction of flow, which allows the desired result to be obtained.
In addition to technical applications (automatic transmissions, music synthesizers), analog computers are used to solve specific computing problems of a practical nature.
Digital computers
There are four main types of digital computers:
- supercomputers;
- large computers (mainframes);
- minicomputers;
- microcomputers.
This is very powerful computers with a performance of over 100 megaflops (1 megaflop is a million floating point operations per second). They are called ultra-fast acting.
These machines are multiprocessor and (or) multi-machine complexes that operate on shared memory and a common field of external devices.
The architecture of supercomputers is based on the ideas of parallelism and pipelined computing.
In these machines, many similar operations are performed in parallel, that is, simultaneously (this is called multiprocessing). Thus, ultra-high performance is provided not for all tasks, but only for tasks that can be parallelized.
A distinctive feature of supercomputers are vector processors equipped with equipment for parallel execution of operations with multidimensional digital objects - vectors and matrices. They have built-in vector registers and a parallel pipelined processing mechanism.
If on a conventional processor the programmer performs operations on each vector component in turn, then on a vector processor he issues vector commands at once.
Supercomputers are used to solve problems in aerodynamics, meteorology, high-energy physics, and geophysics.
Supercomputers have also found their application in the financial sector when processing large volumes of transactions on exchanges.
Mainframes
Mainframes- these are universal, large computers general purpose.
They dominated the computer market until the 1980s.
Mainframes were originally designed to process huge amounts of information.
Mainframes are designed to solve a wide range of scientific and technical problems and are complex and expensive machines. It is advisable to use them in large systems with at least 200 - 300 workplaces.
The largest mainframe manufacturer is IBM.
Mainframes are distinguished by exceptional reliability, high performance, and very high throughput of input and output devices. Thousands of user terminals or microcomputers can be connected to them.
Mainframes are used by major corporations, government agencies, and banks.
Minicomputers
Minicomputers occupy an intermediate position between large computers and microcomputers.
In most cases, minicomputers use RISC and UNIX architecture and play the role of servers to which tens or hundreds of terminals or microcomputers are connected.
Minicomputers are used in large companies, government and scientific institutions, educational institutions, and computer centers to solve problems that microcomputers cannot handle, and for centralized storage and processing of large volumes of information.
The main manufacturers of minicomputers are IT&T, Intel, Hewlett-Packard, and Digital Equipment.
Microcomputers are computers that CPU made in the form of a microprocessor.
Microcomputers for general purpose, designed for one user and controlled by one person - personal computers or abbreviated use PC.
Personal computers
Personal computers Available in stationary (desktop) and portable versions.
Desktop microcomputers in most cases consist of a separate system unit that houses internal devices and nodes, as well as from individual external devices (monitor, keyboard, mouse), without which it is impossible to use modern computers.
If necessary, to system unit microcomputer can be connected to additional external devices (printer, scanner, Acustic systems, joystick).
Portable personal computers
Portable personal computers known primarily in the notebook (laptop) version.
In a laptop, all external and internal devices are connected in one case.
Just like a desktop microcomputer, additional external devices can be connected to a laptop.
PDA, electronic organizers or palmtops
PDAs are considered a separate type of microcomputer ( PDA, electronic organizers, or palmtops), small devices weighing up to 500 grams and fitting on one hand.
They are usually controlled using a screen that is small in size and resolution, pressure-sensitive with a finger or a special pen (stylus), and there is no keyboard or mouse. Some models, however, contain a miniature fixed or retractable keyboard.
Such devices use ultra-efficient processors and Flash drives small in size, so their computing power is not comparable to desktop personal computers.
However, they contain all the features of a personal computer: processor, storage, RAM, monitor, operating system, application software and even games.
Pocket personal computers containing functions are becoming increasingly popular mobile phone(communicators). The built-in communication module allows you not only to make calls, but also to connect to the Internet anywhere there is cellular compatible format (GSM/GPRS, CDMA).
To designate the entire class of handheld computers in English language the phrase Personal Digital Assistant, PDA is used, which can be translated into Russian as “personal digital secretary”.
There are also IBM PC compatible microcomputers (read IBM PC) and IBM PC incompatible microcomputers.
At the end of the 1990s, IBM PC-compatible microcomputers made up more than ninety percent of the world's computer stock. The IBM PC was created by the American company IBM (IBM) in August 1981; during its creation, the principle of open architecture was applied, which means the use of ready-made blocks and devices in the design when assembling a computer, as well as the standardization of methods for connecting computer devices.
The principle of open architecture contributed to the widespread adoption of IBM PC-compatible clone microcomputers. Many companies began assembling them, which, in conditions of free competition, were able to reduce the price of microcomputers several times and energetically introduced the latest technical achievements into production. Users, in turn, were able to independently upgrade their microcomputers and equip them with additional devices from hundreds of manufacturers.
The only IBM PC-incompatible microcomputer that has become relatively widespread is the Mac (Macintosh) from Apple. Runs the Mac OS operating system (currently Mac OS X).
Macintosh computers can be used as full-fledged workstations, specialized computers, and also as office computers.
There is a wide selection of software - system and application, including those compatible in file formats with common PC programs (for example, Microsoft Word, Adobe Photoshop).
Historically, Macintosh computers have been widely used in computer graphics and printing.
In the second half of the 1990s, due to the rapid development of global computer networks, a new type of personal computer appeared - a network computer, which is designed only to work in a computer network.
A network computer does not need its own disk memory, disk drives.
He will get the operating system, programs and information from the network.
It is assumed that network computers will be much cheaper than desktop ones personal computers and will gradually replace them in companies working with specialized applications ( telephone communications, ticket booking), and in educational institutions.
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PC device
Classification of computers.
The entire range of modern computing systems can be divided into three large classes: mini-computers (including personal computers), mainframes, and supercomputers. Currently, these classes differ not so much in appearance, how much in terms of functionality. The existence of different types of computers is determined by the difference in the tasks for which they are intended. Over time, new types of tasks appear, which leads to the emergence of new types of computers. Therefore, the division below is very arbitrary. PC. Modern personal computers have almost the same characteristics as the minicomputers of the eighties: 32- and 64-bit architecture and bus system organization. Currently, the class of minicomputers is extremely diverse: from laptops and palmtops to powerful servers for enterprise-scale systems. The genetic characteristics of this class of machines are the bus organization of the system, in which all devices are “strung” onto a common bus, and the standardization of hardware and software. Mainframes- universal electronic computers for general purposes. Mainframes are actively used in the financial sector and the defense complex and occupy from 10 to 15% of the computer market. Supercomputers-- a special type of computers created to solve extremely complex computational problems (making forecasts, modeling complex phenomena, processing extremely large amounts of information). The principle of operation of a supercomputer is that it is capable of performing several operations in parallel. One of the world's leading companies in the production of supercomputers is Cray Research. Its founder, the legendary man Seymour Cray, built a computer already in the mid-70s Cray-1, which amazed the world with its speed: tens and even hundreds of millions arithmetic operations per second. As is known, the speed of propagation of any signal does not exceed the speed of light in a vacuum - 300 thousand kilometers per second, or 300 million meters per second. If a computer performs 300 million operations per second, then during the execution of one operation the signal has time to travel no more than one meter. It follows that the distance between parts of a supercomputer performing one operation cannot exceed several tens of centimeters. Indeed, Cray supercomputers were very compact and looked like a “donut” with a diameter of less than two meters. This "donut" was only doing calculations. To communicate with a person and deliver data for calculations, several fairly powerful ordinary computers were connected to the donut. In addition, two more types of computers should be distinguished: specialized server computers; embedded stealth computers (microprocessors). In addition to the usual computers with keyboards, monitors, and disk drives, today's world of things is filled with invisible computers. Microprocessor is a computer in miniature. In addition to the processing unit, it contains a control unit and even memory (internal memory cells). This means that the microprocessor is capable of autonomously performing all necessary actions with information. Many components of a modern personal computer contain a miniature computer inside them. Microprocessors have also become widespread in production, where control can be reduced to issuing a limited sequence of commands. Microprocessors are indispensable in modern technology. For example, controlling a modern engine - ensuring fuel economy, limiting the maximum speed, monitoring serviceability, etc. - is unthinkable without the use of microprocessors. Another promising area of their use is household appliances - the use of microprocessors gives them new consumer qualities. Desktop PCs, supporting one workplace constitute the largest group of personal computers, or microcomputers. Before the advent of portable PCs, the words “desktop” and “personal” were synonymous. Desktop PCs are also called desktop computers or office computers(although nowadays office PCs are more often called workstations). The vast majority of home computers are also desktops. Both have almost the same characteristics: 32- and 64-bit architecture and bus organization of the system, use standardized hardware and software. Most desktop PCs fall into two broad groups: IBM-compatible PCs and Apple Macintosh PCs. Computers from these groups are not compatible with each other, i.e. they are completely or partially unable to use the hardware and software products each other. 
Desktop PCs have a system unit containing a power supply, a motherboard with a processor, HDD, disk drives, monitor, keyboard, mouse. They can connect a fax machine, a modem, and other external devices, such as audio speakers. In some home PC models, the system unit and monitor are assembled in a single case ( Apple iMac, Acer Aspire, Compaq Presario). In 1981, the American company IBM launched the production of IBM PC personal computers running the DOS operating system developed by Microsoft specialists. IBM PC computers enjoyed commercial success, and many electronics manufacturers began producing IBM PC clones. This is how a class of IBM-compatible computers emerged that could use most external devices and programs designed for the IBM PC. The principle of compatibility has provided significant savings in cost and time when upgrading old and creating new computers. All IBM-compatible computers can use the Microsoft DOS operating system (PS-DOS for IBM, MS-DOS for PCs from other manufacturers) or Windows and Intel processors(or compatible with them). An alternative to IBM-compatible personal computers are Apple Macintosh computers. TO 
Computers receive, process, store and provide information. The actions of the computer are controlled by the operator. Long sequences of instructions are pre-fixed in programs. Computational operations are performed by the central processor. According to the principles of computer operation, formulated in 1945 by the American mathematician John von Neumann, the central processor consists of two parts. The control device receives program commands and organizes their execution. The arithmetic logic unit performs the calculations. Data is stored in various storage devices. For long-term storage information, permanent media are used that serve to enter data and output work results. To store executables this moment programs and intermediate data use RAM, which works much faster than permanent storage media. Hardware is all the internal components and external devices of a computer - integrated circuits (including microprocessors), disk drives, system and interface boards, monitors, printers, manipulators, modems, etc. Software are sets of computer instructions necessary to control the operation of the computer and perform useful tasks with it. The main feature of the computer design is program principle work. The principle of a program stored in computer memory is considered the most important idea in modern computer architecture. The essence of the idea is that 1) the calculation program is entered into the computer memory and stored in it along with the original numbers; 2) the commands that make up the program are presented in a numeric code in a form no different from numbers.
Internal and external devices.
Computer architecture refers to its logical organization, structure, resources, i.e. means computing system, which can be allocated to the processing process. The architecture of modern PCs is based on backbone-modular principle. The modular principle allows the consumer to choose the computer configuration he needs and, if necessary, upgrade it. The modular organization of the system is based on the backbone (bus) principle of information exchange. Highway or system bus-- this is a set electronic lines, linking together the transfer of data and service signals to the processor, memory and peripheral devices. The exchange of information between individual computer devices is carried out via three multi-bit buses connecting all modules - data bus, address bus And control bus. The data bus width is determined by the processor capacity, i.e. the number of binary bits that the processor processes in one clock cycle. Data on the data bus can be transmitted both from the processor to any device and in the opposite direction, i.e. the data bus is bidirectional. The main operating modes of the processor using the data bus include the following: writing/reading data from random access memory and from external storage devices, reading data from input devices, sending data to output devices. The choice of a subscriber for data exchange is made by the processor, which generates the address code of the device, and for RAM - the address code of the memory cell. The address code is transmitted by address bus, and the signals are transmitted in one direction, from the processor to the devices, i.e. this bus is unidirectional. By control bus signals are transmitted that determine the nature of the exchange of information, and signals that synchronize the interaction of devices participating in the exchange of information. External devices are connected to the buses using interface. An interface is a set of various characteristics any PC peripheral device that determines the organization of information exchange between it and the central processor. In case of incompatibility of interfaces (for example, the system bus interface and the hard drive interface), use controllers.
So that the devices included in the computer can interact with the central processor, IBM-compatible computers provide interrupt system . The interrupt system allows the computer to pause the current activity and switch to others in response to a request, such as pressing a key on the keyboard. After all, on the one hand, it is desirable that the computer be busy with the work assigned to it, and on the other hand, its instant response to any request requiring attention is necessary. Interrupts provide immediate system response.
The computer includes the following components:
- central processing unit (CPU); RAM (memory); storage devices; input devices; output devices; communication devices.
The main unit that determines the capabilities of a computer is the system, or motherboard. It usually houses: a basic microprocessor; RAM; ultra-fast memory, also called cache memory; ROM with system BIOS (basic input/output system), a set of control chips, or chipsets (chipset), auxiliary chips and input/output controllers; CMOS memory with hardware configuration data and a battery to power it; expansion connectors, or slots;
connectors for connecting interface cables hard drives, disk drives, serial and parallel ports, infrared port, and USB universal serial bus; power connectors; voltage converter from 5V to lower to power the processor (for example, i486DX4 processors, Intel Pentium, Intel Pentium Pro consumes 3.3 V, and modern Intel Pentium III and 4, as well as AMD Athlon and Duron consume less than 2V); connector for connecting a keyboard and a number of other components. To connect indicators, buttons and speakers located on the system unit case, there are special miniature plug connectors on the motherboard. Similar connectors serve as jumper contacts when setting the hardware configuration of the system. If all the elements necessary for its operation are concentrated on the motherboard, then it is called All-In-One. For most personal computers, motherboards contain only the main functional units, and the remaining elements are located on separate printed circuit boards(expansion cards) that are installed in expansion slots. For example, a device for forming an image on a monitor screen - a video adapter - is still most often located on a separate expansion card - a video card. All components of the motherboard are connected to each other by a system of conductors (lines) through which information is exchanged. This collection of lines is called a bus. Unlike other connection systems, bus lines are divided into three groups depending on the type of information transmitted: data lines, address lines and control lines. PC buses vary in their own ways. functional purpose. The most important component of any personal computer, its “brain” is a microprocessor (CPU, Central Processing Unit - CPU, or central processing unit), which controls the operation of the computer and performs most of the information processing. The microprocessor is an ultra-large integrated circuit, the degree of integration of which is determined by the size of the crystal and the number of transistors implemented in it. Sometimes integrated circuits are called chips. The basic elements of a microprocessor are transistor switches, on the basis of which, for example, registers are built, which are a set of devices that have two stable states and are designed to store information and quickly access it. The number and width of registers largely determine the architecture of the microprocessor. The commands executed by the microprocessor usually involve arithmetic operations, logical operations, control transfer (conditional and unconditional) and data movement (between registers, RAM and I/O ports). The microprocessor can communicate with external devices thanks to its address, data and control buses, output to special contacts microcircuit housing. The process of communication between the processor and outside world via I/O devices compared to information processes inside it flows hundreds and thousands of times slower. This is due to the fact that input and output devices often operate mechanically (printers, keyboards, mice) and operate slowly. To free the processor from idle time while waiting for the end of operation of such devices, specialized microprocessor-controllers are inserted into the computer. controller -- manager). Having received a command to output information from the computer's central processor, the controller independently controls the operation of the external device. Having finished outputting information, the controller informs the processor that the command has completed execution and is ready to receive the next one. The number of such controllers corresponds to the number of input and output devices connected to the processor. Thus, a separate controller is used to control the operation of the keyboard and mouse. It is known that even a good typist is not able to type on the keyboard more than 300 characters per minute, or 5 characters per second. To determine which of the hundred keys was pressed, a processor not supported by the controller would have to poll the keys at a rate of 500 times per second. Of course, by his standards, this is not God knows what speed. But this means that the processor will spend part of its time not on processing existing information, but on waiting for keyboard keys to be pressed. Thus, the use of special controllers to control I/O devices, while complicating the computer design, simultaneously relieves its central processor from waste. time and improves overall computer performance. The microprocessor, as a universal information processing unit, was developed in 1962. The American corporation Intel in 1971 began producing 4004 microprocessors that worked with four-bit binary digits. Intel's first-born consisted of 2,300 transistors. The improvement of microprocessors proceeded at an accelerated pace. In 1978, the eight-bit microprocessor 8080 was created, and in 1981, the sixteen-bit microprocessor 8086 and 8088. It was on its basis that the production of personal computers began. In 1982, based on the sixteen-bit microprocessor 80286, IBM launched the production of personal computers IBM PC, clones of which became widespread throughout the world. In 1985, the 32-bit i386 microprocessor was created, containing 275 thousand transistors and providing 5 million operations per second. In 1989, the i486 microprocessor appeared, which contained 1.2 million transistors and had a speed of 20 million operations per second. In 1993, the 32-bit Pentium microprocessor was created, which contained 3.1 million transistors and had a speed of 90 million operations per second. Pentium III microprocessors provide performance of 800 million operations per second at a clock frequency of 800 MHz. All of these advances have been achieved through the miniaturization of chips. In 1999, the distance between transistors was reduced to 0.18 microns. But soon the developers will approach the line beyond which fundamental physical limitations begin. Next, the emergence of molecular computing devices is predicted. In them, instead of electrical charges and impulses, chemical states of molecules are supposed to be used to store and transform information.
Memory
All computers use three types of memory: RAM, ROM and external memory. Random access memory (RAM - random access memory) is designed to store information that needs to be accessed frequently, and provides modes for writing, reading and storing it. This type of memory is also called random access memory (RAM). According to the method of storing information, RAM can be static or dynamic. Read-only memory (ROM)- read-only memory) usually contains such information that should not change during the execution of various programs by the microprocessor. Read-only memory is also called ROM (Read Only Memory), which indicates that only read and store modes are provided. The permanent memory is non-volatile, i.e. it can retain information even when the power is turned off. All read-only memory chips, according to the method of entering information into them, are divided into masked, programmable by the manufacturer (ROM), once programmable by the user (Programmable ROM) and repeatedly programmable by the user (Erasable PROM). The latter, in turn, are divided into washable electrically and with the help of ultraviolet irradiation. Electrically erasable EPROM elements include, for example, flash memory chips. They differ from ordinary EPROMs high speed access and quick erasing of recorded information. This type memory is widely used today to store BIOS and other permanent information. Various types RAM and permanent memory can be arranged in the form of a certain hierarchy based on data access time. RAM - a set of special electronic cells, each of which can store a specific 8-digit combination of zeros and ones - 1 byte (8 bits). Each such cell has an address (byte address) and content (byte value). The address is needed to access the contents of the cell, to write and read information. Random access memory (RAM) stores information only while the computer is running. The RAM capacity of a modern computer is 32-128 MB. When a microprocessor performs computational operations, access to any RAM cell must be provided at any time. Therefore, it is called random access memory - RAM (Random Access Memory). RAM is usually made on dynamic type chips with random access (Dynamic Random Access Memory, DRAM). Each bit of such memory is represented as the presence (or absence) of charge on a capacitor formed in the structure of the semiconductor crystal.Static memory
Static memory (SRAM) in modern PCs it is usually used as a second level cache to cache the main amount of RAM. Static memory is usually made on the basis of TTL, CMOS or BiCMOS microcircuits and, according to the method of data access, can be either asynchronous or synchronous. Asynchronous is data access that can be performed at any time. Asynchronous SRAM was used on motherboards for the third to fifth generations of processors. The access time to cells of such memory ranged from 15 ns (33 MHz) to 8 ns (66 MHz). Synchronous memory provides access to data not at random times, but synchronously with clock pulses. In between, the memory can prepare the next piece of data for access.Dynamic memory.
Dynamic memory (DRAM) in modern PCs is usually used as general-purpose RAM, as well as memory for the video adapter. Of the types used in modern and promising PCs dynamic memory the most famous are DRAM and FPM DRAM, EDO DRAM and BEDO DRAM, EDRAM and CDRAM, Synchronous DRAM, DDR SDRAM and SLDRAM, video memory MDRAM, VRAM, WRAM and SGRAM, RDRAM. In dynamic type memory, bits are represented as the absence and presence of charge on a capacitor in the structure of a semiconductor crystal. Structurally, it is implemented in the form of a SIMM module (Single in line memory module). Each bit of information is recorded in a separate memory cell consisting of a capacitor and a transistor. The presence of charge on the capacitor corresponds to 1 in binary code, the absence - 0. When switching, the transistor makes it possible to read a bit of information or write a new bit to an empty memory cell. The search for a cell by address is carried out by special decoding circuits that form a matrix, that is, they intersect the memory crystal with two stripes - horizontally and vertically. When the central processor reports the cell address, the horizontal decoders indicate the desired column, and the vertical decoders indicate the desired row. At the intersection is the desired cell. After finding a cell, its data byte is fetched. Cache memory(cache memory) - a storage device with short access time (several times less than the access time to the main RAM), used for temporary storage of intermediate results and the contents of frequently used cells. In general, data caching is the placement of data in a memory area with more quick access. As an everyday analogy, we can cite the library of a student, whose textbooks he needs every day are on his desk, occasionally read classics are on the bookshelf, and old unnecessary notebooks are folded in drawers. If necessary, the time to access these sources will vary, but the likelihood that you will need a textbook or an old notebook will also vary. IN 
in the world of computer memory, this principle is applicable because faster memory usually costs significantly more than slower ones, but the use of a small amount of fast (but expensive) cache memory, in combination with a large amount of slow (but cheap) memory, allows you to create an acceptable price and speed solution. Caching is especially effective when data is accessed primarily in sequential order. Then, after the first request to read data located in slow (cached) memory, you can pre-read the following blocks of data into the cache memory so that the next request to read data will almost instantly retrieve them from the cache memory. This technique is called read-ahead. Read ahead is used in all modern hard drives, having from 64 to 1024 KB of cache memory, based on dynamic RAM. The data read from the disk is placed in the disk cache memory with some reserve and certain time are stored there. When the same data is accessed again, it is read from the cache memory, which happens 10-1000 times faster. Data caching is also used in processors. Inside the processor die there is a small amount (from 1 to 1024 KB) of very fast static memory operating at the processor frequency. This memory is used to cache the significantly slower RAM, which is based on dynamic RAM. Thus, in different situations, the same memory can be both a cache and a cached memory. Chipset ( chipset) of a motherboard is a set of chips that controls the processor, RAM and ROM, cache memory, system buses and data interfaces, as well as a number of peripheral devices. Chipsets are structurally tied to the type of processor used, and over time life cycle The processor has time to change several generations of chipsets for it, and the first chipsets allow you to use the advantages of the new processor only partially, while the latter allow you to squeeze maximum performance out of the processor and use a wide range of processors. BIOS(Basic Input Output System - basic input/output system) is a part of microcomputer software that supports managing external device adapters, testing and booting the computer. BIOS can also be considered as component hardware, and as one of the software modules of the operating system. The BIOS is built into the PC and contains programs to control the keyboard, video card, disks, ports and other devices before loading any operating system.
The BIOS also contains a power-on test program (POST, Power On Self Test) and a boot loader program. Most modern video adapters, as well as many SCSI controllers, have their own BIOS, which usually complements the system one. In general, the BIOS can be considered as a link between the specific features of the hardware implementation in a PC and the standard requirements of the operating system. The BIOS system in modern computers is implemented in the form of a read-only memory (ROM) chip installed on the computer’s motherboard. To store ROM BIOS in motherboards for the fifth and later generations of processors, electrically reprogrammable memory devices (EEPROM or Flash EEPROM) are used; in older boards or video cards, ultraviolet erasable memory devices (EPROM) are used. Such BIOS elements are called Flash-BIOS. Now the user can quickly update the BIOS by downloading the latest version from the Internet or from a floppy disk. Many modern motherboards are equipped with two BIOS chips, which allows you to store various settings in them and increases system reliability. The not entirely accurate term CMOS RAM (Complementary Metal-Oxide Semiconductor, CMOS or CMOS) refers to non-volatile memory that stores information about the current date, clock readings, computer configuration (amount of RAM, types of drives). The inaccuracy of the term is that CMOS is not the name of the device, but just a technology for manufacturing a microcircuit (this resembles a common mistake: ... an FM radio station ... ", while FM is a method of signal modulation, in no way not associated with a range). Therefore, the terms EEPROM or non-volatile RAM are often used in documentation. The BIOS has a Setup program that can change the contents of CMOS memory, that is, set system configuration parameters. This program is called by a specific key combination: Del - for AWARD BIOS and Ins or F2 - for some versions of AMI BIOS. In general, during the initial boot, the name of the key that should be pressed to launch the Setup program is usually written on the screen. When booting and performing hardware monitoring, the BIOS plays sounds through the computer's speaker that can help diagnose the problem. If everything is in order, then a long beep sounds; if the video card is faulty, then 1 long and 2 short beeps; if the memory is faulty, then repeated short beeps. These codes are described in more detail in the motherboard manual. If the processor is faulty, then there will be no beeps, since the POSTYLE=" program is executed by the processor. System bus can be simplified to represent a set of signal lines, united according to their purpose (data, addresses, control), which also have well-defined electrical characteristics and information transfer protocols. The main responsibility of the system bus is to transfer information between the processor (or processors) and the rest of the computer's electronic components. This bus not only transmits information, but also addresses devices, and also exchanges special service signals. The buses currently in use differ in their width, signal transmission method (serial or parallel), bandwidth, number and type of supported devices, and operating protocol. As a rule, PC buses can be represented in the form of a certain hierarchical structure - bus architecture. A feature of modern PCs is the presence of an ISA bus, inherited from the very first IBM PC models. In addition to it, PCs use EISA, MCA, VLB, PCI, PCMCIA (CardBus) and AGP buses. Buses can be synchronous (transmitting data only on clock pulses) or asynchronous (transmitting data at random times), and also use various arbitration schemes (that is, a way of sharing the bus between several devices). E
If information is exchanged between a peripheral device and a controller, the data line connecting them is called a data interface, or simply an interface. Among the interfaces used in modern and future PCs are EIDE, SCSI, SSA and Fiber Channel, USB, FireWire (IEEE 1394) and DeviceBay. Among the data transfer interfaces, stand out the input/output ports used to connect low-speed peripheral devices: serial port (COM), parallel port (LPT), game port/MIDI port and infrared port (IrDA).
Parallel Port (LPT) On an IBM PC-compatible computer, it is most often used to connect a printer, so it is also called a printer port. A personal computer operates with a maximum of three parallel ports, which are logically named LPT1, LPT2 and LPT3. The cable is connected to the parallel interface adapter via a 25-pin DB-Shell (DB-25) connector, and on the printer side a special 36-pin Centronics connector is used. Since the frequency of transmitted signals can reach tens of kHz, the length of such cables usually does not exceed three meters. Several modifications of parallel high-speed interfaces are known, for example EPP (Enhanced Parallel Port) and ECP (Extended Capabilities Port). These interfaces provide speeds of up to 2-5 MB/s and support two-way data transfer. Currently, both modifications are combined into one standard IEEE 1284. The serial interface is used for most peripheral devices, such as a plotter, remote printer, mouse, and external modem. Until now, adapters with the RS-232C interface (new name EIA-232D) are used for serial communication of IBM PC-compatible computers. A modern IBM PC-compatible computer can use up to four serial ports, logical names COM1, COM2, COM3 and COM4, respectively. The basis of the serial adapter is the UART (Universal Asynchronous Receiver/Transmitter) chip - a universal asynchronous transceiver. Typically the UART 16550A chip is used. It has a 16-character receive and transmit buffer and can also use multiple DMA channels. During transmission, the UART chip converts parallel code into serial code and transmits it bit by bit into the line, framing the original sequence with start, stop and control bits. When receiving data, the UART converts the serial code into parallel (of course, omitting the service characters). An indispensable condition for correct transmission (reception) is the same operating speed of the receiving and transmitting UART, which is ensured by a stable frequency of the quartz resonator. The main advantage of serial transmission is the ability to send data over long distances, typically at least 30 meters. In IBM PC-compatible personal computers, of the 25 signals provided by the RS-232 standard, only 9 are used in accordance with the EIA; Thus, this interface uses both 25- and 9-pin DB-Shell connectors. The PC99 specification (see Desktop PC) emphasizes that the only device using the serial and parallel ports in new PCs can be the printer. Other devices must use FireWire or USB buses. Universal Serial Bus USB(Universal Serial Bus) according to the PC97 specification is a mandatory element of a modern PC. It should gradually replace all previously existing interfaces for connecting peripheral devices (parallel and serial
ports, PS/2 connectors for mouse and keyboard, SCSI interface). The USB standard was developed in 1995 by a consortium of Compaq, DEC, IBM, Microsoft, NEC, Northern Telecom, and in the summer of 1996 the first computers with USB ports. The USB bus is serial interface data transfer for medium and low-speed peripheral devices (for devices requiring higher transfer speeds, the FireWire bus is offered). The USB bus is designed to connect up to 127 devices, while supporting their auto-detection Plug-n-play, as well as the so-called “hot” connection, that is, connection to a running computer without rebooting it. The USB data transfer speed is 12 Mbit/s (i.e., no more than 1.5 MB/s), with a 1.5 Mbit/s subchannel allocated for slow devices. Twisted pair is used as a cable. The length of a USB segment can reach 5 meters. USB devices There are two types: a hub for connecting other devices and a regular device. Hubs can be separate devices or (more commonly) part of other self-powered devices, such as monitors. Modems, keyboards, mice, CD-ROMs, joysticks, tape and disk drives, scanners and printers, digital cameras, monitors (not for signal transmission, but for controlling monitor settings) and other devices are produced with the USB interface. On the Apple iMac, for example, the USB bus serves as the only interface for connecting slow peripheral devices. USB support at the motherboard level is implemented in all modern PCs based on the fifth and sixth generation x86 processors, but BIOS and operating system support is fully implemented only in Windows 98 and Windows NT 5.0. In October 1999, a preliminary version of the USB 2.0 standard was agreed upon, providing for data transfer speeds of 360-480 Mbit/s. For connecting laptops to desktop computers, as well as connecting to them laser printers a wireless interface operating in the infrared range is used. The principle of operation of an infrared port is quite simple: an infrared light-emitting diode (LED) emits a sequence of pulses, which is received by a corresponding photodiode and then converted back into electrical signals. Such communication has a number of advantages: low price, low power consumption and the absence of harmful high-frequency radiation. SCSI interface was developed in the late 1970s by Shugart Associates. Initially known as SASI (Shugart Associates System Interface), after standardization in 1986, already under the name SCSI (pronounced “story”), it became one of the industry standards for connecting peripheral devices - hard drives, tape drives, removable hard and magneto-optical drives, scanners, CD-ROM and CD-R, DVD-ROM, etc. The SCSI interface is parallel. Up to eight devices can be connected to the bus simultaneously, including the main SCSI controller (or host adapter). The SCSI controller is essentially a separate processor and has its own BIOS (which can sometimes be located in Motherboard BIOS boards). It performs all maintenance and management of the SCSI bus, freeing the central processor from doing so. Physically, the SCSI interface is a flat cable with 25- or 50-pin connectors for connecting peripheral devices. The SCSI bus contains eight data lines, followed by a parity line, and nine control lines. The SCSI standard defines two methods of signal transmission - unipolar, or asymmetrical (Single ended) and differential (Differential). In the first case, there is one wire with zero potential (“ground”), relative to which signals are transmitted along data lines with signal levels corresponding to TTL logic. With differential signal transmission, two wires are allocated for each data line, and the signal on this line is obtained by subtracting the potentials at their outputs. This achieves much better noise immunity, which allows you to increase the cable length. The SCSI interface requires terminators - matching resistances that absorb signals at the ends of the cable and prevent the formation of echo. The SCSI interface is generally characterized by high sensitivity to the quality of cables and their length, which may vary depending on the version of the interface. Software for the SCSI interface does not operate on the physical characteristics of the drive (that is, the number of cylinders, heads, etc.), but deals only with logical blocks of data, so in one SCSI chain, for example, a scanner, a hard drive and CD-R drive. Devices are polled by the SCSI controller immediately after power is turned on. At the same time, for SCSI devices, device auto-configuration (Plug-n-play) is implemented using the SCAM (SCSI Configured AutoMagically) protocol, in which SCSI ID values are allocated automatically. Most widely used for standardized management of SCSI devices. software interface ASPI (Advanced SCSI Programming Interface). There are more than a dozen different versions of the SCSI interface. The most significant of them are SCSI-1, Fast SCSI, Fast Wide SCSI, Ultra SCSI, Ultra 2 SCSI. PCI bus specification(Revision 1.0) was introduced by Intel in June 1992 as a processor-independent bus. Taking into account the experience of operating the VL-bus (see VESA bus), PCI developers abandoned the use of the processor bus and introduced another “mezzanine” bus. Thanks to this, the bus can operate in parallel with the processor bus (for example, the processor works with RAM, and at this time the PCI bus data is being exchanged with the video adapter or hard drive). An important factor contributing to the widespread adoption of PCI was that Intel company declared the PCI bus standard open and transferred it to the non-profit organization PCI SIG (PCI Special Interest Group), which began to carry out all work to support it and further development.
The PCI bus is a synchronous 32- or 64-bit bus operating at 33 or 66 MHz. Modern PCs still use a 32-bit, 33 MHz PCI bus, although there are exceptions: Micron Samurai and Intel 450NX AGPSet PC chipsets support a 64-bit bus, and Digital and Sun workstations also use a 64-bit PCI bus. To reduce the number of contacts, PCI uses multiplexing (transferring addresses and data over the same lines at different times). PCI allows the use of boards with a supply voltage of 5 and 3.3 V. The bus supports multiple bus arbiters (multiply bus master). When transferring data, caching and block transfer are supported. PCI bus supports automatic detection and configuration of expansion cards (Plug-n-play). The PCI specification allows you to create multifunctional devices with up to eight functions (for example, modem, sound, network interface, etc.) on one board. The PCI bus in a desktop design has 4 124/188-pin connectors (32/64-bit version) or 8 slots in the CompactPCI design used in industrial and military computers. If a larger number of connectors is needed, then PCI-PCI bridge chips are used (in this case, the bus bandwidth is reduced). The maximum possible data transfer speed on the PCI bus ranges from 132 MB/s for 32-bit/33 MHz to 528 MB/s for 64-bit/66 MHz bus implementations. Video adapter (synonym - video card) designed to store video information and display it on a monitor screen. It directly controls the monitor, as well as the process of displaying information on the screen by changing the horizontal and vertical scanning signals of the CRT monitor, the brightness of image elements and color mixing parameters. The main components of a modern video adapter are the video controller itself, video BIOS, video memory, a special digital-to-analog converter RAMDAC (Random Access Memory Digital to Analog Converter), a quartz oscillator (one or more) and interface chips with the system bus (ISA, VLB, PCI, AGP or other ). An important element of the video subsystem is its own memory. For this purpose, the memory of the video adapter is used, which is often also called video memory, or frame buffer, or part of the PC RAM (in UMA shared memory architecture). All modern video subsystems can operate in one of two main video modes: text or graphic. In text mode, the monitor screen is divided into separate character positions, each of which can display only one character at a time. To convert character codes stored in the video memory of the adapter into bitmaps on the screen, a so-called character generator is used, which is usually a ROM where character images are stored, “laid out” on lines. When receiving a character code, the character generator generates a corresponding binary code at its output, which is then converted into a video signal. Text mode in modern operating systems is used only at the initial boot stage.
IN graphic mode Each point in the image, called a pixel, is allocated between one (monochrome) and 32-bits (color). Graphics mode is often called All Points Addresable mode because it is the only way to access every point in the image. The maximum resolution and number of reproduced colors of a particular video subsystem primarily depend on the total amount of video memory and the number of bits per image element. There are several video card standards. During the existence of IBM PC-compatible personal computers, several generations of video adapters and associated image presentation standards have changed. The main parameters in these standards are resolution (the number of characters, or pixels horizontally and vertically), the number of colors displayed simultaneously on the screen, and the frame rate (which is the frequency at which the image on the monitor screen is redrawn by the scanning device).
Storage
To store programs and data in personal computers, various types of drives are used, the total capacity of which, as a rule, is hundreds of times greater than the capacity of RAM. In relation to a computer, drives can be external or built-in (internal). External drives have their own case and power supply, which saves space inside the computer case and reduces the load on its power supply. Built-in drives are mounted in special mounting bays (drive bays), which allows you to create compact systems, which combine all the necessary devices in the system unit. The drive itself can be considered as a combination of media and the corresponding drive. There are drives with removable and non-removable media. The most common storage devices are listed below. Winchesters (hard discs) Hard drives are the fastest external storage devices. In addition, information stored on a hard drive can be read from it in random order (a disk is a random access device). The disk capacity of a modern personal computer is tens of gigabytes. Several hard drives can be installed in one computer. Optical discs (cdroms) Laser disks, as they are also called, have a capacity of up to 750 megabytes and provide only reading of information once written to them in random access mode. The speed of reading information is determined by the device into which the CD is inserted (cdrom drive). Magneto-optical disks Unlike optical disks, magneto-optical disks allow you to not only read, but also write information. Floppy discs These storage devices are based on a flexible magnetic disk encased in a hard shell. In order to read information stored on a floppy disk, it must be inserted into the floppy disc drive of the computer. The capacity of modern floppy disks is only 1.44 megabytes. In terms of access method, a floppy disk is similar to a hard drive. Zip and Jazz Iomega discs These are relatively new storage media that are designed to replace floppy magnetic disks. They can be considered as fast and large-capacity (100 megabytes - Zip, 1 gigabyte - Jaz) floppy disks. Magnetic tapes Modern magnetic tapes, which store large amounts of information (up to several gigabytes), externally resemble ordinary tape cassettes and are characterized by strictly sequential access to the information contained on them
HDD.
Hard drive (hard drive), a device for permanent storage of information used when working with a computer. “Hard” received its name in contrast to storage media on flexible magnetic tapes and disks. Principles modern technology manufacturing hard drive were developed in 1973 by the American company IBM (IBM). The new device, which could store up to 16 kilobytes of information, had 30 cylinders (tracks) for recording, each of which was divided into 30 sectors. That's why it's called 30/30. Well-known Winchester rifles have a caliber of 30/30, so hard disks also began to be called “Winchesters”. In addition, the hard drive was developed in the American city of Winchester. As a rule, the hard drive is non-removable, but there are models of removable hard drives. The hard drive is mounted on a spindle axis, which is driven by a special motor. It contains from one to ten disks (platters). Engine rotation speed for conventional models can be 3600, 4500, 5400, 7200, 10000, 12000 rpm. The discs themselves are precision-machined ceramic or aluminum plates with a magnetic coating - a thin layer of iron oxide (in earlier models) or chromium oxide (in later models). Each disk (platter) is divided into sequential track-sectors corresponding to the zones of residual magnetization created by the heads. The sector memory capacity is 512 bytes. 
The read-write heads, along with their supporting structure and disks, were originally enclosed in a hermetically sealed housing called a data module. When this module was installed on the disk drive, it automatically connected to the system supplying purified air. In modern hard drives, the disk package is already permanently attached to the drive, the system is not sealed, and there is no forced ventilation. The thickness of the air cushion created by the aerodynamics of the rotating disk and the shape of the head is much thinner than a human hair. The most important part of a hard drive is the read-write head. As a rule, they are located on a special positioner (head actuator). To move the positioner, predominantly linear motors (such as voice coils) are used. Hard drives use several types of heads: monolithic, composite, thin-film, magnetoresistive (MR, Magneto-Resistive), as well as heads with a strong magnetoresistive effect (GMR, Giant Magneto-Resistive). The magnetoresistive head, developed by IBM in the early 1990s, is a combination of two heads: a thin-film write head and a magnetoresistive read head. Such heads make it possible to increase the recording density by almost one and a half times. The GMR head can further increase the recording density. The heads do not touch the surfaces of the disks, but move above them at a distance of fractions of a micron. Inside any hard drive there must be electronic board, which deciphers the commands of the hard drive controller, stabilizes the motor rotation speed, generates signals for the write heads and amplifies them from the read heads. The motor is located under the disk package with the spindle. In earlier models of hard drives, a stepper motor was used to drive positioners, so the distance between the tracks was determined by the size of its step. Modern models use a linear motor, which does not have the discreteness characteristic of stepper motor. Therefore, the magnetic heads are aimed at the track more accurately, which ensures greater recording density on the disks. During the so-called low-level formatting procedure, information is written to the hard drive that determines the layout of the hard drive into cylinders and sectors. The format structure includes various service information: synchronization bytes, identification headers, parity bytes. In modern hard drives, such information is recorded once during the manufacture of the hard drive. Damage to this information due to independent low-level formatting can lead to complete inoperability of the disk and the need to restore this information to factory conditions. The capacity of a hard drive is measured in megabytes. By the end of the 1990s, the average capacity of hard drives for desktop systems reached 15 gigabytes, and in servers and workstations with SCSI interface Hard drives with a capacity of over 50 gigabytes are used. Most modern personal computers use hard drives with a capacity of 10 to 100 gigabytes. IBM has mastered the production of the world's smallest hard drive designed for handheld computers and digital cameras. Its diameter is 25 mm, and the memory capacity is 340 MB.
Floppy disk.
A floppy disk drive (floppy disk, or simply floppy disk) has two motors: one ensures a stable rotation speed of the floppy disk inserted into the drive, and the second moves the read-write heads. The rotation speed of the first motor depends on the type of floppy disk and ranges from 300 to 360 rpm. The motor for moving the heads in these drives is always stepper. With its help, the heads move along a radius from the edge of the disk to its center at discrete intervals. Unlike the hard drive head drive in this device do not “hover” above the surface of the floppy disk, but touch it. The operation of all drive units is controlled by the corresponding controller. 
WITH 
The standard interface for all drives in IBM-compatible computers is the SA-400 (Shugart Associates), the controller of which is connected to the drives via a 34-pin cable. The 5.25" drive uses a blade connector, while the 3.5" drive uses a standard male connector. To connect different types drives are usually combined cables with four connectors included in pairs. On a regular interface cable for the extreme connector, the conductors on pins 10 to 16 are twisted. When using a “straight” cable, it is necessary to change the settings of the jumpers on the drive that determine its number (DS1-DS4). Some Computer BIOS allow you to programmatically change the assignment of the physical address: “first” (A:) and “second” (B:) drive. Unlike hard drives, for floppy drives the order of the drive (A: or B:) is determined precisely by the position of the device on the cable. For each floppy disk size (5.25 or 3.5 inches) there are special drives of the corresponding form factor. The first floppy disk was created by IBM in 1967. It was 8 inches in diameter, had a capacity of 100 KB and was called Flexible disk, that is, floppy disk. It received the name floppy disk later from the English word flop, which means “flapping its wings.” The first sample of a floppy disk was a round plate with a central hole reinforced at the edges. The floppy disk envelope had holes for a spindle that rotated the media, a slot for heads and optocouplers for reading the index. In 1976, the size of the floppy disk was reduced to 5.25 inches and then the diminutive name diskette appeared. At first its volume was 180 KB, then it grew to 360 KB and 1.2 MB. The disadvantage of the flexible disk was poor protection against mechanical damage. In 1980, Sony developed the floppy disk and 3.5-inch floppy drive. The media in it was placed in a solid case made of hard plastic. The only hole for the heads to access the media was covered with a metal curtain with a return spring. Since that time, the floppy disk has ceased to be flexible. Currently, floppy disks are used as the cheapest means Reserve copy (information volume no more than 10 MB), as well as for transferring data from one PC to others, including from portable to stationary PCs. Floppy disks of each standard size (5.25 and 3.5 inches) are usually double sided (DS), single-sided have long become an anachronism. The recording density can be different: single (Single Density, SD), double (Double Density, DD) and high (High Density, HD). Since few people remember about single density anymore, this classification is usually simplified by talking only about double-sided double-density floppy disks (DS/DD, capacity 360 or 720 KB) and double-sided high-density floppy disks (DS/HD, capacity 1.2, 1.44 or 2.88 MB). Floppy disks can be formatted or unformatted. Although factory-formatted floppy disks are slightly more expensive than unformatted ones, the user does not have to waste time formatting them, and they have also undergone additional testing. The most common are 3.5-inch floppy disks. Their magnetic disk is housed in a durable plastic case. The contact area of the magnetic heads with the surface of the disk is closed by a special curtain (latch), which can be moved only inside the drive. The read/write speed for a 3.5-inch drive is about 63 KB/s, the average search time is about 80 ms. There are 80 tracks on the disk (although some formatting programs allow you to use technological tracks 80, 81 and 82 to increase the disk capacity). In the late 1980s, Toshiba, by improving production technology and recording methods, managed to increase the capacity of a floppy disk to 2.88 MB. However, this format did not catch on, and until the end of the 20th century, the vast majority of floppy disks had a capacity of 1.44 MB. Like any other magnetic disk medium, a floppy disk is divided into concentrically located tracks, which, in turn, are divided into sectors. Moving the head to access different tracks is done using a special head positioning drive, which radially moves the magnetic head assembly from one track to another. Track numbering starts from 0, and sectors from 1. This system subsequently moved to hard drives. The principle of recording information on a floppy disk is the same as in a tape recorder, with direct mechanical contact of the head with a magnetic layer deposited on an artificial film. However, unlike a tape recorder, recording here is carried out without high-frequency bias, but by reversing the magnetization of the carrier material until saturation. General principles The design principles of the head unit for reading and writing information have remained almost unchanged over time. Their peculiarity is the presence of two erase heads located on the sides behind the recording/playback head (the so-called tunnel erase).
CD.
A compact disc is a carrier of information in numerical form recorded on an optical (laser) disk. The most widely used are CDs for recording sound (audio disks) and computer CDs (CD-ROM, Compact Disk Read Only Memory). Technology optical disk was developed and demonstrated by Philips in 1979. An optical compact disc consists of a durable, transparent base (polycarbonate or polyvinyl chloride), reflective and protective layers. A layer of sprayed aluminum is usually used as a reflective surface. Digital information is represented on a reflective surface by alternating dimples (non-reflective spots) and areas that reflect light. 
A CD has just one physical track in the shape of a continuous spiral running from the outer diameter of the disc to the inner diameter. Reading information from a CD occurs using a laser beam, which, falling on a light-reflecting area, is deflected to a photodetector, which interprets the signal as a binary unit. The laser beam entering the cavity is not reflected and the photodetector records a binary zero. Computer CDs contain up to 640 megabytes of information, which is enough to record large software systems, games, and multimedia programs. Most computer CDs, like all audio CDs, are read-only. Data is written to CDs when they are manufactured at the factory. But there are special CDs on which you can write (CD-R) and rewrite information (CD-RW). Information from computer CDs is read by the CD drive. Modern personal computers certainly have a CD drive and, if available, sound card can play audio CDs. New generation motherboards support booting the computer from a CD-ROM, which is convenient when installing a new operating system or when checking the computer for viruses. At the end of the 1990s, a new generation of compact discs appeared - DVD (Digital Versatile Disc - digital multi-purpose disc) with high capacity, which are used for recording full-length films, ultra-high quality sound and multimedia computer programs. There are several DVD options that differ in capacity: single-sided, double-sided, single-layer and double-layer. Single-sided single-layer DVDs have a capacity of 4.7 GB of information, double-layer - 8.5 GB, double-sided single-layer - 9.4 GB, double-sided double-layer - 17 GB. The laser beam in a conventional CD-ROM drive has a wavelength of 780 nm, and in DVD devices it ranges from 635 to 650 nm, due to which the recording density has increased significantly.
CD-RW
Currently, CD-ROM drives with the ability to write (CD-R) and rewrite (CD-RW) information have become available to the mass user. Due to the low cost of the drive and blank write-once media, these devices have become widely used for data archiving, backup, storing large volumes of information, etc. CD-R drive(previously called WORM, Write Once - Read Many) also allows you to create (or copy) an audio disc that can be played on any household audio equipment. This allows, for example, to independently create discs with collections of compositions by your favorite artists without loss of quality during the census, since the recording is carried out in digital form. Write-once CD media has very high reliability. The shelf life of a blank disc before recording is from 5 to 10 years, and a recorded disc can be stored, according to various estimates, from 70 to 200 years. The standard disk capacity is 74 minutes (when recording audio data), or 650 MB. There are discs with a diameter of 120 mm and a capacity of 63 and 74 minutes, and with a diameter of 80 mm and a capacity of 18 and 21 minutes. An important advantage CD-R discs is the ability to read them on any CD-ROM drive.Lecture 1 History of the development of computer technology. Target
LectureLogic circuits were created using discrete radio components and electronic vacuum tubes with a filament. Random access memory devices used magnetic drums, acoustic ultrasonic mercury and electromagnetic
Lectures on computer science Lecture Introduction to computer science The term "computer science" (French informatique)
LecturesThe term "informatics" (French informatique) comes from the French words information (information) and automatique (automation) and literally means "information automation".
The basis of the PC is the system unit, which contains:
microprocessor (MP);
random access memory unit (RAM);
read-only memory (ROM); long-term memory on hard magnetic disk(Winchester);
Devices for launching compact discs (CD) and floppy disks (FHD).
There are also boards there: network, video memory, audio processing, modem (modulator-demodulator), interface boards that serve input/output devices: keyboard, display, mouse, printer, etc.
All functional components of the PC are interconnected through a system backbone, which consists of more than three dozen ordered microconductors formed on a printed circuit board. The microprocessor is used to process information: it selects commands from internal memory(RAM or ROM), decrypts and then executes them, performing arithmetic and logical operations. Receives data from an input device and sends the results to output devices. It also produces control and synchronization signals for the coordinated operation of its internal components, controls the operation of the system bus and all peripheral devices. A simplified circuit diagram of the microprocessor is presented in the lower diagram (highlighted by a dashed line with the inscription CPU). It consists of: an arithmetic-logical unit (ALU), which performs arithmetic and logical operations on binary numbers; a block of general purpose registers (GPR) used for temporary storage of processed information (R0 - R5), a stack pointer (R6) and a program counter (R7); a control device (CU) that determines the operating order of all microprocessor nodes. One of the most important characteristics of a microprocessor is its bit depth, determined by the number of ALU and RON bits. Modern microprocessors have 16-, 32-, and 64-bit binary lengths, as well as up to 200 or more different internal instructions.
11. The main functional characteristics of a personal computer are:
1. performance, speed, clock speed. The performance of modern computers is usually measured in millions of operations per second;
2. bit capacity of the microprocessor and interface code buses. Bit capacity is the maximum number of bits of a binary number on which a machine operation can be simultaneously performed, including the operation of transmitting information; the greater the bit depth, the greater, other things being equal, will be the PC performance;
3. types of system and local interfaces. Different types of interfaces provide different speeds of information transfer between machine nodes, allow you to connect a different number of external devices and their different types;
4. RAM capacity. RAM capacity is usually measured in MB. Many modern application programs with RAM having a capacity of less than 16 MB simply do not work or work, but very slowly;
5. capacity of hard disk drive (hard drive). Hard drive capacity is usually measured in GB;
6. type and capacity of floppy disk drives. Currently, floppy disk drives are used, using floppy disks with a diameter of 3.5 inches, having a standard capacity of 1.44 MB;
7. availability, types and capacity of cache memory. Cache memory is a buffered, user-accessible, high-speed memory that is automatically used by the computer to speed up operations with information stored in slower storage devices. The presence of a 256 KB cache memory increases the performance of a personal computer by approximately 20%;
8. type of video monitor and video adapter;
9. availability and type of printer;
10. presence and type of CD drive CD-ROM;
11. presence and type of modem;
12. availability and types of multimedia audio-video tools;
13. available software and type of operating system;
14. hardware and software compatibility with other types of computers. Hardware and software compatibility with other types of computers means the ability to use on a computer, respectively, the same technical elements and software as on other types of machines;
15. ability to work in a computer network;
16. ability to work in multitasking mode. Multitasking mode allows you to perform calculations simultaneously on several programs (multi-program mode) or for several users (multi-user mode);
17. reliability. Reliability is the ability of a system to perform fully and correctly all the functions assigned to it;
18. cost;
19. dimensions weight.
12 . Types of portable personal computers. Today on the market there are portable systems three main categories: laptop, notebook and subnotebook. PDAs (pocket personal computers) stand somewhat aside. The definition of such systems is not very clear, they are based mainly on size and weight; these characteristics are directly related to the capabilities of the system, since the larger the case, the more components can be put into it. Therefore It is not surprising that some manufacturers of portable computers sometimes "misname" the categories of systems they produce - a laptop is called a laptop or vice versa. Below we will consider all the standards of portable systems.
Laptop . This was the name of the first portable computers. Nowadays the most portable systems are called laptops. A typical laptop weighs more than 3 kg and has a size of more than 23 30 5 cm. The appearance of large screens on the modern market has led to an increase in the size (except for the height, which has decreased in some models) of laptop computers. Once the smallest computers, laptops are now becoming ultra-modern machines, comparable in capabilities and performance to desktop systems. An example is the portable Pentium 4, assembled using components from regular desktop computers. The advantages of such a system are lower prices compared to a fully functionally similar laptop, and increased ease of use. Limitations in use - conditional mobility; such a system is more designed for maximum convenience of the manager's desktop. In many cases, laptops are presented by manufacturers as a replacement for desktop systems, or as portable multimedia systems for presentations (“Road systems”). Large active matrix displays with RAM from 32 to 512 MB, hard drives with a capacity of 20 GB or more, CD-ROM and DVD drives, built-in speaker systems, communications and ports for connecting an external display, storage devices and sound systems - here those components that are included in many modern laptop systems. In addition, some "advanced" models also contain a DVD-CD/RW combo drive and Wi-Fi wireless communication device. Most laptops come with docking equipment, allowing you to use them as a "home base" - connect to a computer network and use a full-size monitor and a keyboard. For someone who is constantly on the move, this is much better than having a separate desktop portable system that requires constant data synchronization. Although, of course, you have to pay for everything: the cost of the most powerful laptops is now more than twice the cost of similar desktop systems.
Netbook . The goal of the developers of portable systems of this type was to create a computer that was smaller in all respects than a laptop. A netbook weighs 2-3 kg, has a smaller display than a laptop, lower resolution and multimedia capabilities (but do not consider these machines weak). Many of them have hard drives and memory no less than laptops, and most even contain CD-ROMs and sound adapters. Designed not as a replacement, but rather as a complement to a desktop system, netbooks are hardly amazing in their capabilities, but they are full-featured travel computers. There are a wide range of options and hardware configurations available for netbooks because they are designed for a wide range of users, from professionals to salespeople who use the bare minimum of features.
Subnotebook . The subnotebook is significantly smaller than its counterparts. It's perfect for the traveler who doesn't need the advanced capabilities of a large, overly heavy machine, but wants the functionality of a desktop computer on the go and the ability to connect to an office network. Subnotebooks typically don't have an internal floppy drive, but sometimes have a connector for connecting an external drive. There are also no CD-ROM drives or other bulky components, but there is a relatively large, high-quality display, significant storage space, and a full-size (by laptop standards) keyboard is not uncommon on these machines. Some subnotebook models (for example, the IBM THINKPAD 570) are equipped with a special module with which you can connect “no hardware”, such as a CD-ROM or DVD drive. There are subnotebooks designed specifically for “cool” people (such as senior management personnel ) who primarily use email and scheduling tools and want a system that's lightweight, sleek, and impressive. The cost of such systems is at the level (or higher) of laptops. An example would be an Acer Pentium III (CPU 1.13 MHz) or Acer Pentium IV (CPU 1.2 MHz) subnotebook with a 20 GB hard drive and an approximate size of 25 x 15 2 cm.
Palmtops . This category appeared on the market relatively recently. The name of these computers matches their size - they can fit in the palm of your hand. This category of portable systems does not include networked personal assistants or systems running Windows CE. Palmtops are fully functional computers with operating system as in desktop models. The palmtop keyboard is often a basic set of keys, and smaller in size. Therefore, such computers are best suited for sending Email or fax on the go, to solve other small problems. A typical representative of a palmtop is the Libretto series of computers manufactured by Toshiba (according to a more modern classification, they are classified as subnotebooks). Such a computer weighs about 700 grams, has an 8-inch screen, and a trakpoint pointing device is integrated into the small keyboard. Such palmtops are inferior in performance to other types of laptop computers, but have one advantage - you can install the Windows operating system and all the necessary applications on it.
Pocket PCs . These are computers and organizers that can be controlled by Palm OC, Windows CE, Pocket PC, EPOC systems. They can be keyboard-based (Handheld PC) or keyboard-less (Palm size PC). In addition, there are smartphones - a combination pocket computer and mobile phone. Such computers are not full-fledged in the sense that they require connection to a stationary machine to exchange data. Technologies of mobile computer systems. From a time when the word "Portable" meant "a case with a handle," laptop computers, like their desktop predecessors, have changed a lot. Today's portable systems can compete with desktop systems in almost every way. Many companies offer them to mobile users as primary computers.
Personal computers have developed rapidly over the past 20 years. A personal computer (PC) is designed to serve a single workstation and can meet the needs of small businesses and individuals. With the advent of the Internet, the popularity of PCs has increased significantly, since using a personal computer you can use scientific, reference, educational and entertainment information.
Computer is a universal technical system capable of clearly performing the sequence of operations of a specific program. A personal computer (PC) can be used by one person without the help of maintenance personnel. User interaction occurs through many media, from alphanumeric or graphical dialogue via a display, keyboard and mouse to virtual reality devices.
IBM's first personal computer was introduced to the market in 1981. Computers were equipped with a new operating system for the first time MS-DOS system Microsoft. The computer was named IBM PC and was built on the Intel 8088 microprocessor. The appearance of the IBM PC was a revolutionary event in the development of information technologies thanks to what was laid down when creating the computer the principle of open (modular) architecture. As a result, it became possible to quite easily change the configuration of a computer or upgrade it by replacing obsolete blocks and assemblies.
Most modern computers are IBM PC-compatible personal computers. This means that they are compatible with the IBM PC computer, developed in 1981 by IBM. The concept of “compatibility” means both the ability to execute on any model of an IBM-compatible computer any program written for this type of computer (software compatibility), and the ability independent connection to various IBM computers of various external devices (hardware compatibility).
The most important role in the development of IBM PC-compatible computers was played by the open architecture principle. IBM did not make the computer a single one-piece device, but provided the ability to assemble it from independently manufactured parts.
Over the years, several generations of IBM PC machines have changed, primarily characterized by the type of processor (see below). Historically, the first and long-outdated IBM computer model was the IBM PC XT (eXtended Technology) model based on the Intel 8086 microprocessor. Introduced in 1984.
The IBM PC AT (Advanced Technology) computer standard, based on the Intel 80286 microprocessor, can be considered the starting point in the history of modern IBM PC-compatible computers. Modern computers are also identified as "AT-compatible".
Personal IBM PC-compatible computers are the most widely used, their power is constantly increasing, and their scope is growing. However, their capabilities are still limited, and their use is not always justified.
Personal computers can be roughly divided for professional and household purposes, but due to the cost of litigation hardware, the line between them is blurred. Since 1999, an international certification standard has been introduced - specification PC99:
− mass personal computer (Consumer PC)
− business personal computer (Office PC)
− portable personal computer (Mobile PC)
− workstation (WorkStation)
− entertainment personal computer (Entertaiment PC)
Most personal computers on the market fall into the mainstream PC category. Business PCs have a minimum of graphics and sound reproduction capabilities. Portable PCs are distinguished by the presence
means of remote access communication (computer communications). Workstations - increased requirements for data storage devices. Entertainment PCs - the main emphasis is on the means of reproducing graphics and sound.
Basic PC configuration
Despite the variety of types, shapes and architectures of personal computers, most PCs include the following components: system unit, display, keyboard, mouse (or other pointing device) and peripheral devices. Depending on the needs and capabilities of users, the composition of the periphery can be expanded with an audio system with a synthesizer, modem, printer or scanner.
Typically, personal computers consist of three parts (blocks):
− system unit;
− a keyboard that allows you to enter characters into the computer;
− monitor (or display) – for displaying text and graphic information.
The system unit includes all the main components of a personal computer. Its most important component is the motherboard, or system board. It contains electronic modules that make up the basic set of computer electronics:
− central processor – the main chip that performs computational and logical operations;
− random access memory (random access memory - RAM) - a set of chips for storing data and programs while the computer is running;
− ROM (read-only memory) – a microcircuit for long-term storage of data and programs;
− buses – sets of conductors for exchanging signals between internal components of a computer
− chipset – a set of chips that control the operation of the internal components of the computer and determine functionality motherboard;
− connectors (slots) – extensions for connecting additional devices;
− device controllers, etc.
The system unit also houses:
− power supply that converts mains voltage into D.C. low voltage, for powering computer components;
− disk drives (drives) for reading and writing floppy disks, magneto-optical disks, CDs and DVD video disks;
− hard disk drive (hard drive).
All external devices are connected to the system unit: monitor, keyboard, mouse, printer, modem, scanner, sound speakers etc.
Monitor(display) displays text and graphic information on the screen, data entered from the keyboard or output from the computer, messages computer system, copies of documents and other information important to the user.
Keyboard designed for entering commands and data into a computer.
Mouse allows you to point to screen elements using a pointer and perform certain operations by clicking on buttons.
Printer outputs text and graphic black-and-white and color information as a hard copy. Output can be done on paper or film.
Modem designed to connect a computer to a telephone line.
Scanner provides input into a PC of text or graphic, black and white or color information for its further processing.
PC video system: monitor (purpose, classification, specifications) and video card.
Monitors
The first computers did not have monitors, there was only a set of blinking LEDs and results printed on a printer. With the development of computer technology, monitors appeared and now they are a necessary part of the basic configuration of a personal computer.
A monitor (display) is a standard output device designed for visual display of text and graphic data. Depending on the principle of operation, monitors are divided into:
Cathode ray tube monitors;
Liquid crystal displays.
Cathode ray tube monitor
A cathode ray tube monitor is similar to a television. A cathode ray tube is an electron vacuum device in the form of a glass flask, in the neck of which there is an electron tube, and at the bottom there is a screen with a layer of phosphor. When heated, the electron gun emits a stream of electrons that move at high speed towards the screen. Electron flow (electronic
the beam) passes through a focusing and deflection coil, which directs it to a specific point on the phosphor coating of the screen. Under the influence of electrons, the phosphor emits light that the user sees. The phosphor is characterized by the emission time after the action of the electron flow. The electron beam moves quite quickly, streaking the screen in lines from left to right and top to bottom. During scanning, that is, moving across the screen, the beam affects those elementary areas of the phosphor coating where an image can appear. The intensity of the beam constantly changes, which causes the corresponding areas of the screen to glow. Since the glow disappears very quickly, the electron beam must continuously run across the screen, restoring it.
The emission time and the glow update frequency must correspond to each other. Mostly, the vertical scan frequency is 70-85 Hz, that is, the glow on the screen is renewed 70-85 times
per second. Reducing the refresh rate causes the image to flicker, which causes eye strain. Accordingly, increasing the refresh rate leads to blurring or doubling of the image contours.
Monitors can have either a fixed refresh rate or different frequencies in a certain range. There are two scanning modes: Interlaced and Non Interlaced. Usually, ordinal scanning is used. The beam scans the screen line by line from top to bottom, forming an image in one pass. In interlaced scanning mode, the beam scans the screen from top to bottom, but in two passes: first the odd lines, then the even ones. An interlaced scan takes half the time to complete a full frame in non-interlaced mode. Therefore, the update time for the two modes is the same.
Screens for cathode ray tube monitors can be convex or flat. The standard monitor is convex. Some models use Trinitron technology, in which the screen surface has a slight horizontal curvature, while the vertical screen is completely flat. This screen has less glare and improved image quality. The only drawback can be considered the high price.
Liquid Crystal Display (LCD)
Liquid crystal displays have a glare-free flat screen and low power consumption of electrical energy (5 W, compared to a cathode ray tube monitor that consumes 100 W). There are three types of liquid crystal displays:
Monochrome with passive matrix;
Color with passive matrix;
Color with active matrix.
In liquid crystal displays, a polarizing filter creates two different wavelengths of light. A light wave passes through a liquid crystal cell. Each cell has its own color. Liquid crystals are molecules that can flow as a liquid. This substance transmits light, but under the influence electric charge, the molecules change their orientation.
In passive matrix liquid crystal displays, each cell is driven by an electrical charge (voltage) that is transmitted through a transistor circuit in accordance with the arrangement of the cells in the rows and columns of the screen matrix. The cell responds to an incoming voltage pulse.
In active matrix displays, each cell is equipped with a separate transistor switch. This provides higher image brightness than passive matrix displays because each cell is exposed to a constant rather than pulsed electric field. Accordingly, the active matrix consumes more energy. In addition, having a separate transistor switch for each cell complicates production, which in turn increases their price.
Monochrome and color monitors
Based on the set of shades of displayed colors, monitors are divided into color and black and white (monochrome). Monochrome monitors are cheaper, but are not suitable for working with the Windows operating system.
Color monitors use more complex imaging techniques. In monochrome cathode ray tubes there is one electron gun, in color tubes there are three. Monochrome screen cathode ray tube coated with a phosphor of the same color (yellow, white or green emission). The screen of a color cathode ray tube consists of phosphor triads (with red, green and blue radiation). Combinations of three colors provide a great variety of output shades.
Basic parameters of monitors
From the user's point of view, the main characteristics of a monitor are diagonal size, resolution, refresh rate and protection class.
Monitor size . Monitor screens are measured diagonally in inches. Sizes range from 9 inches (23 cm) to 42 inches (106 cm). How bigger screen, the more expensive the monitor. Common sizes are 14, 15, 17, 19 and 21 inches. Large monitors are best used for desktop publishing and graphic works, in which you need to see all the details of the image. Optimal for mass use are 15- and 17-inch monitors.
Resolution.In graphic mode, the image on the monitor screen consists of dots (pixels). The number of horizontal and vertical points that the monitor is capable of reproducing
to give clearly and separately is called its resolving power. The expression “resolution 800x600” means that the monitor can display 600 horizontal lines of 800 dots each. The following resolution modes are standard: 800x600, 1024x768, 1152x864 and higher. This property of the monitor is determined by the size of the dot (grain) of the screen. The screen grain size of modern monitors does not exceed 0.28 mm. The higher the resolution, the better quality Images. Image quality is also related to screen size. So, for satisfactory image quality in the 800x600 mode on a 15-inch monitor, you can limit the grain size to 0.28 mm; for a 14-inch monitor with the same grain size in the same video mode, the quality small parts the image will be a little worse.
Regeneration frequency . This parameter is otherwise called the frame rate. It shows how many times per second the monitor can completely refresh the image on the screen. The refresh rate is measured in Hertz (Hz). The higher the frequency, the less eye fatigue and the more time you can work continuously. Today, the minimum acceptable frequency is 75 Hz, normal - 85 Hz, comfortable - 100 Hz or more. This parameter also depends on the characteristics of the video adapter.
Monitor protection class is determined by the standard to which the monitor meets in terms of safety requirements. It is now generally accepted international standards TCO-92, TCO-95 and TCO-99, limiting the levels of electromagnetic radiation, ergometric and environmental standards, within limits safe for human health.
Video adapter
The monitor is controlled by a special board called a video adapter (video card). Together with the monitor, the video card creates the video subsystem of the personal computer. The first computers did not have a video card. There was a screen memory section in the RAM where the processor stored image data. The screen controller read data on the brightness of individual screen points from memory cells and controlled the scanning of the horizontal beam of the monitor's electron gun.
When moving from monochrome monitors to color monitors and with an increase in screen resolution, the video memory area became insufficient to store graphic data, and the processor did not have time to process images. All operations related to screen control were allocated to a separate unit - the video adapter.
The video adapter takes the form of a separate expansion card, which is inserted into a specific slot on the motherboard (in modern PCs this is the AGP slot). The video adapter performs the functions of a video controller, video processor and video memory.
Over the life of the PC, several video adapter standards have changed:
MDA (Monochrom Display Adapter) - monochrome,
CGA(Color Graphics Adapter) - 4 colors,
EGA(Enhanced Graphics Adapter) -16 colors,
VGA (Video Graphics Array) - 256 colors,
SVGA (Super VGA) - up to 16.7 million colors.
All programs designed for IBM-compatible computers are designed to meet these standards. Formed graphic image stored in the internal memory of the video adapter, which is called video memory. The required video memory capacity depends on the given resolution and color palette, therefore, to work in modes with high resolution and full-color gamma, you need as much video memory as possible. If until recently video adapters with 2-4 MB of video memory were typical, today a capacity of 32-64 MB is considered normal. Most modern video cards have the ability to expand video memory up to 128 MB, as well as video acceleration. The essence of this property is that part of the image construction operations can occur without performing mathematical calculations in the main processor, but purely in hardware - by converting data in special video accelerator chips.
Video accelerators can be included in the video adapter, or can be supplied as a separate expansion card installed on the motherboard and connected to the video card. There are two types of video accelerators: for flat (2D) and three-dimensional (3D) graphics. The former are more effective for working with general-purpose application programs and optimized for Windows OS, while others are focused on working with various multimedia and entertainment programs.
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