System bus. Local buses. Computer bus

At the heart of the motherboard are various buses that carry signals to the system components. A bus is a common communication channel used in a computer to connect two or more system components.

There is a certain hierarchy of PC buses, which is expressed in the fact that each slower bus is connected to a faster one. Modern computer systems include three, four, or more buses. Each system device is connected to a bus, with certain devices (most often chipsets) acting as a bridge between the buses.

• Processor bus. This high-speed bus is the core of the chipset and motherboard. It is used primarily by the processor to transfer data between the cache or main memory and the northbridge of the chipset. In systems based on Pentium processors, this bus operates at 66, 100, 133, 200, 266, 400, 533, 800, or 1066 MHz and is 64 bits wide (8 bytes).
• AGP bus. This 32-bit bus operates at 66 (AGP 1x), 133 (AGP 2x), 266 (AGP 4x) or 533 MHz (AGP 8x), provides bandwidth up to 2133 MB / s and is intended for connecting a video adapter. It is connected to the northbridge or memory controller (MCH) of the system logic chipset.
• PCI-Express bus. Third generation PCI bus. The PCI-Expres bus is a differential signaling bus that a northbridge or southbridge can carry. PCI-Express performance is expressed in the number of lanes. Each bidirectional link provides data rates of 2.5 or 5 Gbps in both directions (250 or 500 MB / s effective value). The slot with single lane support is designated PCI-Express x1. PCI-Express video adapters are usually installed in x16 slot, which provides data transfer rates of 4 or 8 Gb / s in each direction.
• PCI-X bus. This is the second generation of the PCI bus, which offers faster data transfer rates but is also backward compatible with PCI. This bus is mainly used in workstations and servers. PCI-X supports 64-bit slots, backward compatible with 64-bit and 32-bit PCI adapters. PCI-X v1 runs at 133 MHz, while PCI-X 2.0 supports up to 533 MHz. Typically, PCI-X 2.0 bandwidth is split across multiple PCI-X and PCI slots. Although some south bridges support the PCI-X bus, most often a dedicated chip is required to support it.
• PCI bus. This 32-bit bus operates at 33 MHz; it has been used since systems based on 486 processors. There is currently a 66 MHz implementation of this bus. It is controlled by a PCI controller, a component of the north bridge or MCH controller of the system logic chipset. The system board has connectors, usually four or more, that can accommodate network adapters, SCSI adapters, video adapters, and other hardware that supports this interface. PCI-X and PCI-Express buses are more efficient PCI bus implementations; motherboards and systems supporting this bus appeared on the market in mid-2004.
• ISA bus. This 16-bit bus, running at 8 MHz, was first used in AT systems in 1984 (the original version of the IBM PC was 8-bit and ran at 5 MHz). This bus was widespread, but was dropped from the PC99 specification. Implemented using the south bridge. Most often, a Super I / O chip is connected to it.

Some modern motherboards contain a special connector called the Audio Modem Riser (AMR) or Communications and Networking Riser (CNR). These specialized connectors are designed for expansion cards that provide networking and communication functions. It should be noted that these connectors are not a universal bus interface, so only a few of the specialized AMR or CNR boards are on the open market. Typically, these boards are included with a specific motherboard. Their design allows you to easily create both standard and extended motherboards without having to reserve space for additional chips. Most motherboards that provide standard networking and modem functionality are PCI-based, as the AMR / CNR connectors have a highly specialized purpose.

There are also hidden buses in modern motherboards, which do not appear in any way as sockets or connectors. This refers to the buses used to connect the components of the chipset, such as the hub interface and the LPC bus. The Hub interface is a four-cycle (4x) 8-bit bus with an operating frequency of 66 MHz, which is used to exchange data between the MCH and ICH components of a chipset (hub architecture). The bandwidth of the hub interface reaches 266 MB / s, which allows it to be used to connect chipset components in low-cost designs. Several modern workstation and server chipsets, as well as Intel's latest 9xx series for desktops, use faster versions of this hub interface. Third-party chipset manufacturers also implement their own high-speed bus designs that interconnect the individual components in the chipset.

For similar purposes, the LPC bus is also intended, which is a 4-bit bus with a maximum bandwidth of 16.67 MB / s and is used as a more economical option compared to the ISA bus. Typically the LPC bus is used to connect the Super I / O or ROM BIOS components of the motherboard to the main chipset. The LPC bus has approximately the same operating frequency, but uses significantly fewer contacts. It allows you to completely eliminate the use of the ISA bus in motherboards.

A system logic chipset is like a conductor who directs an orchestra of system components, allowing each of them to connect to its own bus.

• ISA, EISA, VL-Bus and MCA buses are not used in modern motherboard designs. MB / s. Megabyte per second.
• ISA. Industry Standard Architecture, also known as 8-bit PC / XT or 16-bit AT-Bus.
• LPC. Low Pin Count bus (bus with a small number of contacts).
• VL-Bus. VESA (Video Electronics Standards Association) Local Bus (ISA extension).
• MCA. MicroChannel Architecture (IBM PS / 2 systems).
• PC-Card. 16-bit PCMCIA (Personal Computer Memory Card International Association) interface. CardBus. 32-bit PC-Card bus.
• Hub Interface. Intel 8xx series chipset bus.
• PCI. Peripheral Component Interconnect (bus of interaction of peripheral components).
• AGP. Accelerated Graphics Port.
• RS-232. Standard serial port, 115.2 KB / s.
• RS-232 HS. High speed serial port, 230.4 kb / s.
• IEEE-1284 Parallel. Standard bi-directional parallel port.
• IEEE-1284 EPP / ECP. Enhanced Parallel Port / Extended Capabilities Port (parallel port with enhanced capabilities).
• USB. Universal Serial Bus (universal serial bus).
• IEEE-1394. FireWire bus, also called i.Link.
• ATA PIO. AT Attachment (also known as IDE) Programmed I / O (ATA bus with programmable I / O).
• ATA-UDMA. AT Attachment Ultra DMA (ATA bus Ultra-DMA mode).
• SCSI. Small Computer System Interface (interface of small computer systems).
• FPM. Fast Page Mode (fast page mode).
• EDO. Extended Data Out (extended I / O).
• SDRAM. Synchronous Dynamic RAM (synchronous dynamic RAM).
• RDRAM. Rambus Dynamic RAM (dynamic RAM technology Rambus).
• RDRAM Dual. Dual channel RDRAM (simultaneous operation).
• DDR-SDRAM. Double-Data Rate SDRAM (Double-rate SDRAM).
• CPU FSB. Processor Bus (or Front-Side Bus).
• Hub interface. Intel 8xx chipset bus.
• HyperTransport. AMD Chipset Bus.
• V-link. VIA Technologies Chipset Bus.
• MuTIOL. SiS Chipset Bus.
• DDR2. New generation of DDR memory.

To improve efficiency, many buses carry out multiple data transmission cycles per clock cycle. This means that the data transfer rate is higher than it might seem at first glance. There is a fairly simple way to improve bus performance with backward compatible components.

After studying this topic, you will learn:

What is the structural diagram of a computer;
- what is the principle of programmed control;
- what is the purpose of the system bus;
- which means the principle of open architecture used in building a computer.

Block diagram of a computer

In the previous topics, you got acquainted with the purpose and characteristics of the main computer devices. Obviously, all these devices cannot work separately, but only as part of the entire computer. Therefore, to understand how a computer processes information, it is necessary to consider the structure of a computer and the basic principles of the interaction of its devices.

In accordance with the purpose of a computer as an information processing tool, the interaction of the devices included in it should be organized in such a way as to ensure the main stages of data processing.

To clarify what has been said, consider the block diagram of information processing by a computer shown in Figure 21.1, on which the main stages of this process already familiar to you from Section 1 are indicated in the top row. The implementation of each of these stages is determined by the presence of corresponding devices in the computer structure. Obviously, the input and output of information is carried out using input devices (keyboard, mouse, etc.) and output (monitor, printer, etc.). Internal and external memory is used to store information on various media (magnetic or optical disks, magnetic tapes, etc.).

Figure: 21.1. Block diagram of a computer

Dark arrows indicate the exchange of information between various computer devices. Dashed lines with arrows represent control signals from the processor. Light empty arrows represent input and output streams, respectively.

A computer is a system of interconnected components. Structurally, all the main components of a computer are combined in a system unit, which is the most important part of a personal computer.

System unit and motherboard

The following devices are located inside the system unit:

♦ microprocessor;
♦ internal computer memory;
♦ floppy drives - external memory devices;
♦ system bus;
♦ electronic circuits that provide communication between various computer components;
♦ electromechanical part of the computer, including the power supply, ventilation, indication and protection systems.

Computer layout IBM 286

Modern PC layout

All the listed devices that make up the system unit are placed in a case, and there are various types of cases. The type of case of the system unit depends on the type of personal computer and determines the size, location and number of installed components of the system unit. For stationary personal computers, the most common cases are horizontal or desktop (desktop) or in the form of a tower (tower). In portable computers, the system unit is combined with a monitor and is made in the booksize standard, that is, the size of a book.

The technical (hardware) basis of a personal computer is the system or motherboard.

The motherboard is the main board in the computer system unit. It contains the most important microcircuits - the processor and memory. The motherboard connects various devices into a single whole, provides working conditions and communication of the main components of a personal computer. The processor provides not only information conversion, but also control of the operation of all other computer devices.

The computer is based on the so-called principle of program control. In accordance with it, program commands and data are stored in an encoded form in RAM. When the computer is running, the commands to be executed and the data they require are read in turn from memory and sent to the processor, where they are decrypted and then executed. The results of the execution of various commands, in turn, can be written to memory or transferred to various output devices. The speed at which a processor performs information processing operations is a decisive factor in its performance. The fact is that any information (numbers, text, pictures, music, etc.) is stored and processed on a computer only in digital form. Therefore, its processing is reduced to the execution of various arithmetic and logical operations by the processor, provided by its instruction system.

System bus

To ensure information exchange between various devices of a computer, it must be provided with some kind of highway to move information flows. Let's clarify this idea with a small example.

You know that the life of a big city is a constant stream of people and vehicles moving in different directions. Often the speed of traffic or people flow depends not on the speed of a car, bicycle or pedestrian, but on the capacity of the city's transport network, on its underground and surface highways.

The computer does not move traffic, but information flows along the corresponding information highway. The role of such an information highway connecting with each other all computer devices is performed by the system bus located inside the system unit. Simplistically, the system bus can be thought of as a group of cables and electrical (conductive) lines on the system board.

All main units of a personal computer are connected to the system bus (Figure 21.2). Its main function is to provide interaction between the processor and the rest of the electronic components of the computer. This bus transfers data, memory addresses and control information.

Figure: 21.2. The purpose of the system bus

The speed of information processing by a personal computer depends on the type of system bus, as well as on the type of processor. The main characteristics of the system bus are the bit width and performance of the communication channel.

Bus width determines the number of bits of information transmitted simultaneously from one device to another.

The system buses of the first personal computers could transmit only 8 bits of information using 8 data lines in the form of 8 parallel conductors. Further development of computers led to the creation of a 16-bit system bus, and then its bit depth increased to 32 and further to 64 bits. An increase in the width of the data bus led to an increase in the speed of information exchange, and an increase in the width of the address bus provided a larger amount of RAM.

Tire performance is determined by the amount of information that can be transmitted through it in one second.

Like highways, the throughput of which depends on the number of lanes on the road, the performance of the system bus is largely determined by its capacity. The higher the bus width, the more bits of information can be simultaneously transmitted over it, for example, from the processor to memory. This leads to faster data exchange and freeing up the processor for other tasks.

However, the system bus, as the main information highway, cannot provide sufficient performance for external devices. To solve this problem, local buses began to be used in the computer, which connect the microprocessor with various memory, input and output devices. The purpose of local buses is similar to the purpose of circuit or ring roads around a large city, which relieve the load on the main highways.

Ports

The computer communicates with various input and output devices through ports. Some devices provide external connection to ports through connectors, which are also commonly referred to as ports. These connectors are located on the back of the system unit. Floppy drives, hard drives, and laser drives are installed and connected inside the system unit. Distinguish between wired ( serial and parallel, USB, Fire Wire) and wireless ( infrared, bluetooth) ports.

Parallel ports

This type of port is used to connect external devices that need to transmit a large amount of information over a short distance. A parallel port typically transmits 8 bits of data simultaneously over 8 parallel wires. A printer, scanner are connected to the parallel port. The number of parallel ports on a computer does not exceed three, and they have respectively the logical names LPT1, LPT2, LPT3 (from the English Line PrinTer - printer line).

Serial ports

This type of ports is used to connect mice, modems and many other devices to the system unit. A serial data stream of 1 bit goes through such a port. This can be compared with how traffic is moving on a road with one lane. Serial data transmission is used over long distances. Therefore, serial ports are often referred to as communication ports. The number of communication ports does not exceed four, and they are assigned names from COM1 to COM4 (COMmunication port).

USB port

The USB (Universal Serial Bus) port is currently the most common means of connecting medium-speed and low-speed peripheral devices to a computer. The USB port uses a serial communication method. The most widespread is the high-speed USB 2.0 port. If your computer lacks USB ports, you can eliminate this drawback by purchasing a USB hub that has several of these ports.

With its built-in power lines, USB often allows devices to be used without their own power supply.

FireWire port

FireWire (IEEE 1394) - fiery wire (pronounced "fire wire") is a serial port that supports a data transfer rate of 400 Mbps. This port is used to connect video devices to the computer, such as, for example, a VCR, as well as other devices that require fast transfer of large amounts of information, such as external hard drives.

FireWire ports are plug and play and hot pluggable.

FireWire ports are of two types. Most desktop computers use 6-pin ports, while laptops use 4-pin ports.

Infrared wireless port

Data transmission is carried out via an optical channel in the infrared range. Remote controls for household appliances - TVs, VCRs, etc. work in a similar way. The range of the infrared port is several meters, while it is necessary to provide direct visibility between the receiver and the transmitter.

The infrared port is usually used to connect to a mobile phone that has the same port. This makes it possible to access the Internet using a mobile phone, which is most important for portable laptops in non-stationary conditions.

Bluetooth wireless module

One Bluetooth adapter allows wireless connection of about 100 devices located at a distance of up to 10 m.At the same time, various types of wireless devices can be connected to a computer equipped with such an adapter: mobile phones, printers, mice, keyboards, etc. Data transmission is carried out over a radio channel to frequency range 2.2-2.4 GHz. The main advantage is a stable connection regardless of the relative position of the receiver and transmitter. If your computer does not have a built-in Bluetooth module, then it can be purchased separately and connected via a USB port.

Other system board components

The system board, in addition to the above-mentioned essential components of the computer, contains additional microcircuits, switches and jumpers. All these devices are necessary to ensure the interaction of various computer devices, to set their operating modes. For example, the motherboard can have microcircuits that require different supply voltages. The operating parameters of the devices are set by switches on the motherboard.

In any system unit there are mandatory components that ensure the operation of a computer - a power supply, a system clock, a battery, signal indicators on the front of the system unit.

The system clock determines the speed at which the computer performs operations, which is related to the clock frequency, measured in megahertz (1 MHz is equal to 1 million cycles per second).

The system clock determines the rhythm of the entire computer, synchronizes the operation of most components of its motherboard.

Expansion cards and slots provide the implementation of the so-called principle of open architecture for building a modern personal computer. A slot is the connector where the board is inserted. The presence of expansion slots on the motherboard allows you to consider a personal computer as a device that can be modified. The expansion of the computer's capabilities is carried out by installing an expansion card in the slot. Some device located outside the system unit is connected to the connector of this board using a cable.

Instead of the term "expansion board" the names "card", "adapter" are often used. The most common expansion cards are video cards, sound cards, and internal modems.

Understanding open computer architecture

The technology of manufacturing computers is developing rapidly, which ensures a continuous increase in their performance, memory capacity and, as a result, the ability to solve increasingly complex problems. Some devices are rapidly improving, others are being created, fundamentally new. With such a rapid development of technology, it is necessary to provide for such a principle of building a computer that would allow using the devices (blocks) already in it, as well as replacing them with new, more advanced ones without changing the design. As cities are built according to the laws of architecture, so the computer device must develop according to certain laws. The main principle of building a modern personal computer is the principle of open architecture: each new block must be software and hardware compatible with the previously created ones. This means that a modern personal computer can be simply presented as a children's construction set made of blocks familiar to everyone. In a computer, it is just as easy to replace old cubes (blocks) with new ones, wherever they are located, as a result of which the computer's work is not only not disturbed, but becomes more productive. It is the principle of open architecture that allows you not to throw away, but to upgrade a previously purchased computer, easily replacing outdated blocks in it with more advanced and convenient ones, as well as to purchase and install new blocks and nodes. Moreover, the places for their installation (connectors) in all computers are standard and do not require any changes in the design of the computer itself.

The principle of open architecture is the rules for building a computer, according to which each new node (block) must be compatible with the old one and be easily installed in the same place in the computer. 

test questions

1. What are the main blocks that form the structure of a computer and how are they related to the stages of information processing?

2. What is the role of a personal computer processor in information processing?

3. What is the principle of programmed control?

4. What are the purpose and main components of the system unit?

5. What types of cases of the system unit do you know?

6. What is the motherboard for?

7. What is the purpose of the system bus in a personal computer?

8. What is the analogy between the system bus and transport highways?

9. What characteristics of the system bus do you know?

10. What is a computer port? What types of ports are there and what is their difference?

11. Why do we need expansion cards?

12. Why do I need to have expansion slots?

13. What is the principle of open architecture?

14. What do you know from fiction, popular science publications, television programs and films about the possibilities and uses of computers of the future?

It was eight-bit, i.e. it was possible to transmit 8 bits at the same time. The system buses of modern PCs, such as the Pentiurr IV, are 64-bit.

The bus bandwidth is determined by the number of bytes of information transferred over the bus per second. To determine the bus bandwidth it is necessary to smart-live the bus clock frequency by its bit width. For example, for a 16-bit ISA bus, the bandwidth is defined as

(16 bit * 8.33 MHz): 8 \u003d 16.66 MB / s.

When calculating the bandwidth, for example, the AGP bus, you should take into account its mode of operation: due to the doubling of the clock frequency of the video processor and the change in the data transfer protocol, it was possible to increase the bus bandwidth by two (2x mode) or four (4 * mode) times, which is equivalent to increasing the bus clock frequency by the corresponding number of times (up to 133 and 266 MHz, respectively).

External devices are connected to the buses via an interface (Interface), which is a set of various characteristics of a PC peripheral device that determine the organization of information exchange between it and the central processor.

These characteristics include electrical and time parameters, a set of control signals, a data exchange protocol and design features of the connection. Data exchange between PC components is only possible if the interfaces of these components are compatible.

PC bus standards

The principle of IBM compatibility implies the standardization of the interfaces of individual PC components, which, in turn, determines the flexibility of the system as a whole, i.e. the ability to change the system configuration as needed and connect various peripheral devices. In case of incompatibility of interfaces, controllers are used. In addition, flexibility and system unification is achieved through the introduction of intermediate standard interfaces such as serial and parallel interfaces. These interfaces are required to operate the most important I / O peripherals.

The system bus is designed to exchange information between the CPU, memory and other devices included in the system.

System buses include:

GTL, 64-bit, 66, 100 and 133 MHz;

EV6, the specification of which allows its clock frequency to be increased to 377 MHz.

I / O buses are improved in accordance with the development of PC peripherals. Table 2.5 shows the characteristics of some I / O buses.

ISA bus was considered a PC standard for many years, but it is still retained in some PCs along with the modern PCI bus. Intel has partnered with Microsoft to develop a phase-out strategy for the ISA bus. Initially, it is planned to exclude ISA connectors on the motherboard, and later to exclude ISA slots and connect floppy drives, mice, keyboards, scanners to the USB bus, and hard drives, CD-ROM drives, DVD-ROM drives to the SHEE 1394 bus. However, there is a huge a pair of PCs with an ISA bus and related components suggests that the 16-bit ISA bus will be in demand for some time to come.

EISA bus was a further development of the ISA bus in the direction of increasing system performance and compatibility of its components. The bus did not gain wide acceptance due to its high cost and bandwidth, and the decreasing bandwidth of the VESA bus that appeared on the market.

VESA bus, or VLB, is designed to connect the CPU with fast peripheral devices and is an extension of the ISA bus for exchanging video data. In the days when the CPU 80486 processor dominated the computer market, the VLB bus was quite popular, but now it has been replaced by the more efficient PCI bus.

PCI bus was developed by Intel for the Pentium processor and is a completely new bus. The underlying principle behind the PCI bus is the use of so-called bridges, which provide communication between the PCI bus and other types of buses. The PCI bus implements the Bus Mastering principle, which implies the ability of an external device to control the bus when sending data (without the participation of the CPU).

During the transfer of information, the device supporting Bus Mastering seizes the bus and becomes the master. In this case, the central processor is free to solve other tasks while data transfer is taking place. In modern motherboards, the PCI bus clock speed is set to half the system bus clock speed, i.e. with a system bus clock of 66 MHz, the PCI bus will operate at 33 MHz. The PCI bus has now become the de facto standard among I / O buses. In fig. 2.6 given the architecture of the PCI bus

AGP bus - high-speed local bus I / O, designed exclusively for the needs of the video system. It connects the video adapter (ZO-accelerator) with the PC's system memory. The AGP bus was developed based on the PCI bus architecture, so it is also 32-bit. However, at the same time, it has additional opportunities to increase the bandwidth, in particular, through the use of higher clock frequencies.

If the standard 32-bit PCI bus has a clock frequency of 33 MHz, which provides a theoretical PCI bandwidth of 33 x 32 \u003d 1056 Mbit / s \u003d 132 MB / s, then the AGP bus is clocked by a signal with a frequency of 66 MHz, so its bandwidth is mode 1x is 66 x 32 \u003d 264 MB / s; in 2x mode, the equivalent clock frequency is 132 MHz, and the bandwidth is 528 MB / s; in 4x mode the bandwidth is about 1 GB / s.

USB bus was developed by the leaders of the computer and telecommunications industry Compaq, DEC, IBM, Intel, Microsoft for connecting peripheral devices outside the PC case. The speed of information exchange via the USB bus is 12 Mbit / s or 15 Mbyte / s. Peripheral devices such as a keyboard, mouse, joystick, printer can be connected to computers equipped with a USB bus without turning off the power. TJSB bus supports Plug & Play technology.

When a peripheral is connected, it is automatically configured. All peripheral devices must be equipped with USB connectors and connected to the PC through a separate plug-in unit called a USB hub, or hub, through which up to 127 peripheral devices can be connected to the PC. The USB bus architecture is shown in Fig. 2.7.

SCSI bus (Small Computer System Interface) provides a data transfer rate of up to 320 MB / s and provides for connecting up to eight devices to one adapter: hard drives, CD-ROM drives, scanners, photo and video cameras. A distinctive feature of the SCSI bus is that it is a cable loop. With PC buses (ISA or PCI), the SCSI bus is connected through a Host Adapter. Each device connected to the bus has its own identification number (ID). Any device connected to the SCSI bus can initiate an exchange with another device.

In fig. 2.8 shows the connection of peripheral devices to a PC using the SCSI bus. There is a wide range of SCSI versions, from the first SCSI I, which has a maximum bandwidth of 5 MB / s, to the Ultra 320 version, which has a maximum bandwidth of 320 MB / s. The IEEE 1394 bus can compete with the SCSI bus.

IEEE 1394 bus Is a high-speed local serial bus standard developed by Apple and Texas Instruments. The IEEE 1394 bus is designed to exchange digital information between PCs and other electronic devices, especially for connecting hard drives and audio and video processing devices, as well as for multimedia applications. It is capable of transmitting data at speeds up to 1600 Mbit / s, working simultaneously with several devices transmitting data at different speeds, like SCSI. Like USB, the IEEE 1394 bus fully supports Plug & Play technology, including the ability to install components without turning off the power of the PC.

Almost any device capable of working with SCSI can be connected to a computer via the IEEE 1394 interface. These include all kinds of disk drives, including hard drives, optical drives, CD-ROMs, DVDs, digital camcorders, tape recorders, and many other peripheral devices. Thanks to such wide possibilities, this bus has become the most promising for combining computers with consumer electronics. Currently, IEEE 1394 adapters for the PCI bus are already being produced.

Questions for students to take notes:

1. Definition of the tire

2. Purpose of tires

3. Bus architecture

4. The concept of the bus width.

5. The concept of bus bandwidth

6. PC bus interface

7. Principle of IBM compatibility

8. Types of tires and their characteristics (fill in the table)

Buses are known to be used to transfer data from the central processor to other devices in a personal computer. In order to coordinate the transmission of data to individual components operating at their own frequency, a chipset is used - a set of controllers structurally united into the North and South bridges. The North Bridge is responsible for the exchange of information with the RAM and the video system, the South Bridge is responsible for the functioning of other devices connected through the corresponding connectors - hard drives, optical drives, as well as devices on the motherboard (built-in audio system, network device, etc.), and for external devices - keyboard, mouse, etc.

The system board schematic is shown below.

To connect the processor with bridges, the FSB (Front Side Bus) bus (the most commonly used today Hyper-Transport and SCI) is used, the north bridge (sometimes called the system controller) allows the most productive devices to function - a video adapter using the PCI Express 16x bus and an operational memory through the memory bus. The south bridge provides operation of slower devices connected using expansion cards (audio cards, network cards, video cards, etc.) via PCI buses and PCI Express bus, optical drives and hard drives via ATA buses (formerly called IDE, now called PATA (Parallel ATA) and more modern SATA buses Even slower devices are connected to the south bridge via the LPC bus - a BIOS chip, a multicontroller for communicating with external devices via serial and parallel ports - a keyboard, mouse, printer, etc.

Note that in most modern computers the central processor (Intel Nehalem, AMD Sledgehammer) performs the functions of the north bridge.

The computer has several buses over which data is transmitted. The main one is the bus between the central processor and the North Bridge. You can read about the frequency of this bus in the section on processors. The next bus is between the processor and the RAM (it used to be between the North Bridge and the RAM). You can find out about its characteristics from the section on RAM. The buses that lead to expansion cards, which we will describe below, remain unconsidered.

The data bus transfers data directly, and the more lines it has, the more data can be transferred per clock cycle, so the number of lines is constantly increasing. To transfer data inside the computer, a special bus is used, which consists of three parts, through which data, addresses, control signals, as well as grounding, voltage, etc. are transmitted. That is, practically data is transmitted in three parts: address bus, data bus and bus management. The number of lines on the address bus determines the maximum address space where data can be sent, mainly to RAM. The 8086 processor had 20 lines for the address and could address 2 20 \u003d 1 megabytes of memory, 286 had 24 lines (2 24 \u003d 16 megabytes), 386 had 32 lines (2 32 \u003d 4 gigabytes), modern computers have more than 32 lines. That is, the more lines in the address bus, the more RAM the motherboard supports.

The data bus transfers data directly and the more lines it has, the more data can be transferred per clock cycle. Therefore, the number of lines is constantly increasing, from 8 in the first computers to 32 in Pentium systems.

Through the connectors of the motherboard, through the inserted boards, information is transmitted to / from the processor to external devices in relation to the motherboard. Naturally, these connectors cannot transfer more data than the internal system bus supports, and usually less, depending on the type of bus with which the expansion cards work. There are several types of buses and, accordingly, connectors: ISA, EISA, PCI and others. In the latest models of computers, the more efficient PCI-E bus is used. But quite a few devices still work with less efficient buses. Therefore, modern motherboards have up to 5 different buses and their corresponding connectors.

Let's take a closer look at the available tires.

ISA bus (Industry Standart Architecture) appeared long ago and has been a standard for a long time. Now it is hopelessly outdated. In total, the first XT models had 8 lines for data, which allowed for byte transfer, 20 address lines for addressing up to 1 megabyte of memory, and another 34 lines for other purposes. During the transition to the PC AT model, another 36 lines were added, among them 8 for data and 4 for address. The 8-bit one was used in the PC XT, had 62 pins and allowed 1 MB of memory to be addressed. Then came the 16-bit (sometimes called AT BUS), operates at a frequency of 8 MHz at a speed of 16 Mb / s, allows addressing up to 16 megabytes. It consists of two parts, the first of which corresponds to the 8-bit ISA bus slot. The extra 8 bits are used for additional I / O addresses and contain 36 slots (so you can install 8-bit cards in a 16-bit slot). However, this device had a clock frequency of 8.33 MHz, worked slowly, so other buses appeared.

Currently, the Plug-an d-Play (PnP) standard is used, which allows automatic configuration when installing a new device. The system itself determines the type of device, I / O port address, interrupt number and direct memory access (DMA) channel. However, older tires have difficulty in using this standard. Thus, the ISA bus was developed before the advent of PnP. Therefore, not all devices that are connected to this bus can be automatically configured. To get out of the existing situation in Windows 9x there is a list of devices that can be connected to the computer and which are installed themselves.

The ISA bus has the following restrictions:

The presence of a 16-bit bus, that is, the ability to simultaneously send two bytes;

Maximum clock frequency 8.33 MHz;

Lack of sharing of interrupts and DMA channels for several cards in different slots;

Inability to programmatically disable the card in case of device conflict;

Lack of software management of I / O port addresses, interrupt lines and direct access channels.

To install an ISA card on an EISA bus, you usually need to have a configuration file in order to run the EISA bus configuration utility, which will then allocate resources for the card.

When installing a new device, you need to make it physically and logically compatible. Physical alignment means that the type of connector, the number of pins on the plug and the connector must match each other. Logical alignment means that the contacts through which the voltage is supplied, where there is a ground, etc. must be clearly defined. In this case, the signal sent on one contact must be identified by the receiving device as a data transfer signal, and not as a control signal. All this is determined by the bus standard.

This standard is set, as a rule, by the manufacturer who has begun the mass production of new devices. These include the EIDE bus for connecting hard drives, serial and parallel ports, a bus for displaying graphics, a bus for connecting expansion cards, a USB bus, IrDA, etc., which have their own standards. However, in practice, buses are often used to refer to the bus to which the expansion board is connected. Therefore, in this book and beyond, the bus will simply be referred to as PCI, VESA, etc. In conclusion, we note that the first buses for the computer were called Multibus1... They were produced in two versions: PC / XT bus and PC / AT bus and had 7 lines for hardware interrupts. Later they were replaced by the ISA bus.

Bus MCA (Microchannel - microchannel) appeared in 1987, developed by IBM and installed on a PS / 2 ISA computer. There are two types: 16- and 32-bit. 32-bit works with a frequency of 10 MHz, with a data transfer rate of up to 20 Mb / s, allows addressing up to 4 gigabytes. The expansion card could be self-recognized and automatically configured by the computer. The main drawback is the inconsistency with the ISA bus, for which the main devices were developed, so this architecture has not found widespread use.

TireEISA (Extended ISA - Extended ISA) was released by a group of companies competing with IBM in 1988, since the MCA bus was closed and could only be used by IBM, it is also outdated. The advantages include its compatibility with the ISA connector due to the location of the connectors in two layers, on one ISA, on the second - EISA. This bus is 32-bit, operates at 8.33 MHz and provides a maximum data transfer rate of up to 33 Mb / s. The configuration is set by software, not using switches.

So that when installing a card that requires an ISA connector, the two layers are not closed, the connector has a cap that does not allow connecting to the bottom pins. The EISA card contains a cut-out in the place of the plug that allows you to bypass the plug.

Due to its high cost, the EISA bus was not widely used in personal computers, but was used in workstations and servers.

Tire SCSI (Small Computer System Interface) is designed to connect large arrays of devices such as hard disks, optical drives, tape drives, printers, etc. to the bus. Therefore, it is used mainly in server computers or computers with a RAID system. It is practically not used in home computers.

SCSI-1 appeared in 1986, had 8 data lines, each device with its own number, and the adapter was assigned a number 7. The rest of the devices are numbered from 0 to 6, and the number is set manually on the back of the connected device or using jumpers. Devices on the bus can exchange information with each other without the participation of an adapter, which in this case determines who can transmit data to whom. At the same time, when information passes through him, he takes part in this. Bus frequency - 5 MHz, maximum number of connected devices - 8.

Fast SCSI appeared in 1991 and had 8 data lines and an improved cable connector. Bus frequency - 10 MHz, bandwidth - 10 MB / s, maximum number of connected devices - 8.

Wide SCSI had 16 lines for data transmission, bus frequency - 10 MHz, bandwidth - 20 MB / sec, maximum number of connected devices - 16.

Ultra SCSI appeared in 1992, had 8 data lines, bus frequency - 20 MHz, bandwidth - 20 MB / s, maximum number of connected devices - 4-8.

Ultra Wide SCSI had 16 lines for data transmission, bus frequency - 20 MHz, bandwidth - 40 MB / sec, maximum number of connected devices - 4 - 16.

Ultra 2 SCSI appeared in 1997, had 8 data lines, bus frequency - 10 MHz, bandwidth - 40 MB / s, maximum number of connected devices - 8.

Ultra 2 Wide SCSI had 16 lines for data transmission, bus frequency - 40 MHz, bandwidth - 80 MB / s, maximum number of connected devices - 16.

Ultra 3 SCSI had 16 lines for data transmission, bus frequency - 40 MHz, throughput - 160 MB / s, maximum number of connected devices - 16.

Ultra -320 SCSI had 16 lines for data transmission, bus frequency - 80 MHz, bandwidth - 320 MB / s, maximum number of connected devices - 16.

Ultra -640 SCSI appeared in 2003, had 16 data lines, bus frequency - 160 MHz, bandwidth - 640 MB / s, maximum number of connected devices - 16.

Later, the technology began to develop SAS (Serial Attached SCSI) for working with hard drives and tape drives. You can connect SATA devices to a SAS connector, but not vice versa. Provides 1.5, 3.0, 6.0 Gbps throughput, 12 Gbps is expected. Allows you to connect not only 3.5 "drives, but also 2.5" drives.

The adapter itself is located on the motherboard (like a Mac) or on an expansion card. The card is inserted into a PCI slot. The Mac SCSI cable has a DB25 female connector, the same as the parallel port. If you accidentally connect it to a printer or a parallel port on a computer, or, conversely, connect a printer cable to a SCSI device, the chips of the device to which they are connected may burn out.

When data is transmitted over a cable, a so-called "standing wave" can occur in it. To avoid it, a special plug is used that extinguishes it. Moreover, this plug should be one and located at the end of the cable. SCSI devices can have two connectors, one of which connects to the SCSI bus, and the other, if it is at the end of the cable, must have a plug. If there are two plugs on two devices on the line, then they can interfere with each other from performing their role.

The SCSI bus works somewhat differently with hard disks than other standards, considering a disk not as records with heads, cylinders, sectors, but as a sequence of logical records. When the SCSI adapter receives information from the central processor for a hard disk write to a specific address, it translates it into a logical record number. As a result, if the hard disk is replaced with any SCSI device of this adapter, it will work, but if installed in other adapters, the system may not read the data on the disk conversion to the new structure, all information on the disk will be destroyed.

Other devices (optical drives, Iomega) have special drivers so you can move them freely from one system to another. In the same computer, you can use both devices connected to the SCSI adapter and EIDE at the same time.

SCSI devices require termination at the end of the cable that connects them. As a rule, it is installed at the factory on each of the devices. Therefore, when installing all devices except the last one, you need to remove them. If the devices connected to the SCSI bus do not support the Plug & Play standard, then they need to set the device number using jumpers. It should be borne in mind that some adapters require devices numbered 0 and 1 to be hard drives.

EIDE bus designed for connecting hard drives and optical drives. Also called as ATA or RATA (parallel ATA). Now it is superseded by the SATA bus, but, nevertheless, it is installed on modern motherboards, since several optical drives can be connected to it (two for each connector). This is discussed in more detail in the paragraph on hard drives. The first floppy drives were connected to a computer using cards containing a disk controller. Over time, when the size of the microcircuits decreased, the controller began to be installed on the hard disk, and the floppy disk controller on the motherboard, so it became possible to connect hard drives directly through the connector on the motherboard.

This is how the IDE bus appeared, which is part of the ISA bus, which is brought out to a special connector (in modern devices there are two connectors) on the motherboard. First, a bus standard was developed called ATA, then ATAPI, which made it possible to work with optical drives. Over time, an extended version of EIDE with the ATA standard appeared, and later an extension of the standard - ATAPI. If there are more devices connected to the EIDE connector than the computer can support, then you need to install a special card to which you can connect more devices.

The first standards used hard drives connected to the board using special cards that housed the controller to the ISA bus. Over time, the size of electronic components decreased and they began to be installed on the hard drive itself. Then the disks began to be connected to the board via an IDE connector, then two connectors appeared, and up to two devices could be connected to each of the connectors, the performance increased, addressing of logical blocks was introduced, it became possible to connect optical drives, and all this was supported by the EIDE standard, which works with a clock frequency of 8.33 MHz. The first devices worked with the ATA standard, and then ATAPI, which made it possible to connect an optical device to the channel. Since it became possible to transmit 2 bytes simultaneously over the channel in one clock cycle, the transfer rate over the same lines reached 16.6 MB / s. Over time, data was transmitted in one clock cycle, not only during the transition from high to low voltage, but also during the transition from low to high. This standard is called Ultra ATA or ATA33, as it allows data transfer at a speed of 33.3 MB / s.

Later, the ATA66 standard appeared, in which the clock frequency in the channel increased to 16.7 MHz and data transmission occurs at a speed of 66.7 MB / s. The cable for connecting the hard drive to the motherboard is already different and contains 80 wires instead of 40, as was the case with previous standards. This cable uses 40 wires to connect devices. If you connect a device capable of operating in ATA33 to this channel, or a device operating in the ATA66 standard to the ATA33 bus, the device will operate at a speed of 33.3 MB / s. In some ATA boards and its ATAPI extension, it is possible to connect devices with different speeds to one bus without sacrificing performance, but it is still better to divide them into different channels.

Cable for work with the IDE ATA (AT-Bus) standard - 16-bit, has 40 wires. The XT IDE cable (8 bit) also has 40 cores, but is not ATA compatible, that is, it cannot be used for the IDE standard.

There are two modes of DMA channel operation: Singleword and Multiword. Singleword DMA has mode 0, which runs at 2.08 mb / s, mode 1 at 4.16, mode 2 at 8.33, and Multiword DMA has mode 0, which runs at 4.12, mode 1 at 13.3, mode 2 at 16.6 mb / s. ... Ultra DMA mode has mode 0 operating at speed - 16.6, mode 1 - 25, 2 - 33.

In addition, there are other PIO modes, from 0 and higher, and the higher the number, the faster the bus.

ATA-2 mode works in PIO Mode 3 multiword DMA Mode 1, supports LBA and CHS. Fast ATA -2 supports Multiword DMA mode 2 and PIO mode 4. ATA3 is an extension of ATA2 with Smart, that is, it improves power consumption. ATA / ATAPI-4 - ATA3 extension, has Ultra DMA, ATAPI interface. E-IDE supports PIO mode3, with multiword DMA mode 1 and works with LBA and CHS. Ultra DMA requires an 80-conductor cable with 40-pin connectors with shielding. The IDE Mastering standard allows an external device to control the system bus for data transfer without controlling the processor bus, but using such a bus eliminates DMA channel allocation problems and capacity limitations. In particular, it works with 8- or 16-bit data. Then came the modes of operation ATA-3 (another name EIDE), ATA-4 (frequency 16.7, 25, 33.3, another name Ultra ATA / 33), ATA-5 (frequency 66 MHz, also called Ultra ATA / 66), ATA-6 (100 MHz frequency, another name Ultra DMA 100 or UDMA 5 (100)), ATA-7 (frequency 133 MHz, another name Ultra DMA 133 or UDMA 6 (133)), ATA-8 (in development).

Tire VESA (Video Electronics Standard s Association - Association for video electronic standards or VL -BUS or VLB or VESA local bus) is outdated, the first appeared after the ISA bus and had four times faster speed than ISA, but it had some limitations, in particular, it was possible have only 2-3 connectors, which undoubtedly reduced the ability of the computer. It is a bus for connecting a display, but it can be used for other devices, it is not an extension of the ISA bus (like the previous buses). This card is directly connected to the CPU bus, bypassing the system bus. Works with a system bus frequency of up to 66 MHz, was used mainly with 486, sometimes 386 computers for video cards and hard drives. A new version 2.0 was released for the Pentium, but it did not receive wide distribution and is currently practically not used.

PCI bus (Peripheral Component Interconnect - connection of peripheral components) is also not based on the ISA bus and is a completely independent, synchronous bus, developed by Intel, the first versions operated at 33 MHz, had a 32-bit (or 64-bit) channel and is independent of central processor, that is, it allows data to be transferred while the processor is busy with other calculations. The theoretical throughput of the bus was 133 MB / s, in reality - 80 MB / s. This bus is still widely used today.

The PCI bus began development at the same time as the ISA bus, but was completed later. PCI has more data lanes than ISA and is faster than ISA, with a total of 124 pins in the slot. The bus provides data transfer error detection and operates without a cable plug. In addition, it allows you to configure the connected device during installation, that is, the computer reads information from the device's memory, where its main parameters are stored. The bus can work not only with a certain set of microcircuits on the motherboard, but also with different devices, as well as in other types of computers. In addition, the PCI bus is able to share interrupts and DMA channels for different devices, which was the impetus for its active implementation, while the ISA bus could not provide this.

You can connect cards to the PCI bus connector: with power supply at 5 V (key 50, 51 pins), 3.3 V (key 12,13) \u200b\u200band universal (key in 12, 13, 50, 51 pins). A 32-bit slot has 62 pins on each side, a 64-bit one - 94. This bus allows you to connect up to four devices simultaneously, that is, it can have up to four connectors. To use more connected devices, a special microcircuit is used - a bus bridge, to connect two buses. For industrial devices, there is a Compact PCI standard with 8 slots.

While the PCI bus was being developed, other industries also developed. The clock frequency of the internal bus has increased to 100, 150 and higher MHz, the number of data transmission lines has increased to 64 and continues to increase, but the PCI bus type remains 32-bit, but in the future the PCI bus will also develop.

Each slot has 256 eight-bit registers that hold configuration parameters. After turning on the power of the computer, a request for bus configuration occurs during the execution of the Post program; after setting the parameters, the bus can perform I / O operations. The main advantage of the bus is that data transfer occurs without the involvement of the central processor, that is, during the transfer of data from one device to another, the central processor can do its own thing.

PCI 1.0 is 32-bit with 132 MB / s bandwidth, addressing up to 4 gigabytes, and PCI 2.0 is 64-bit with 528 MB / s bandwidth. This bus is adapted for Plug & Play technology, that is, the boards are configured in software. For industrial applications, the Compact PCI standard is used, in which up to eight devices can be installed simultaneously.

Interrupt conflicts in the PCI bus are resolved by allowing the bus to process each device in turn. The PCI bus provides 32 data lines at a clock frequency of 33 MHz, then it became 64-bit, with a clock frequency of 66 MHz, and the new version of the bus can be used to insert old PCI cards, as well as a new card in the old slot. Newer PCI versions can increase the clock speed and allow older expansion cards to be used for their operation, as well as to install new cards in old slots.

AGP bus (Accelerated Graphics Port) was developed by Intel in 1997 specifically to work with a video card, at 66 MHz it has a 32-bit data bus. Currently superseded by the PCI -E bus. The bus allows you to use pipelining, that is, to send data in contiguous packets. The PCI bus sends the previous datum and the address for the next datum, after which time delays occur, while the AGP bus sends multiple addresses and multiple data one after the other to reduce delays. You can queue up to 256 requests and support two queues for high and low priority read / write operations. Dual transmission, that is, the transmission of two data per cycle instead of one, allows you to have a bandwidth at a frequency of 66 MHz up to 528 MB / s. Allows you to work at frequencies up to 100 MHz and higher with higher bandwidth. Quad transfer allows transfers up to 1,056 MB / s.

There are several standards for the AGP bus: AGP 1X, 2X, 4X, Pro and 8X. Most cards work with 4X and 8X standard. In RAM, not only parts of the image are stored, but also graphic textures. So that the video system can access only those areas of memory that touch it, a special table GART (Graphics Address Remapping Table) is used, which defines these areas of memory.

In the bus, it is possible for the video processor to directly access the RAM sections, as well as to the video memory, and process textures there in the DiMe (Direct Memory Execution) mode, while the addressing is the same. The bus is used for Pentium Pro, Pentium II, Pentium III and Pentium IV processors, but it can work with Pentium processors as well.

SATA (Serial ATA) is an evolution of the IDE interface. Its feature is not parallel transmission of data, but serial, which, although slower, allows using higher frequencies without the need for signal synchronization. The first SATA 1.x standard could operate at a frequency of 1.5 GHz with a bandwidth of 1.2 Gb / s (losses due to the transfer of a large amount of service information). Standard 2.x operates at 3 GHz with a bandwidth of up to 2.4 Gb / s and standard 3.0 at a frequency of 6.0 Gb / s with a bandwidth of 4.8 Gb / s.

To connect devices inside the system unit, they are connected to the information connector with 7 SATA pins on the motherboard and a 15-pin power cable to the power supply. There are devices that allow you to connect both a 15-pin cable and a 4-pin Molex electrical power cable. Keep in mind that connecting two cables at the same time can burn the device.

There are adapters from SATA to IDE and vice versa.

eSATA (External SATA - external SATA) is intended for connecting devices in hot-swap mode, that is, when the computer is turned on. In order to be able to do this in Windows XP, you need to install the AHCI driver. It was established in 2004. Has a connector similar to SATA, but added connector shielding. Therefore, it is not compatible with the SATA connector, since it is electrically compatible, but physically not. The cable length is increased to 2 meters (1 meter for SATA).

There is a combined eSATA + USB \u003d Power eSATA , which has not only data lines, but also power lines.

PCI - E (or PCI Express or PCI-E) appeared in 2002, uses star communication between devices, allows hot swapping of devices. There are several options x1, x2, x4, x8, x12, x16, x32, which have different connectors. The lower the number, the fewer pins and the shorter the connector length. Devices that are intended for the x8 connector can be connected to the connectors with a large number, in this case, x12, x16, x32. This rule applies to other species.

There are three standards. Standard 1.0 allows one-way transmission for x1 - 2 Gbps, in two directions - 4 Gbps for x1. The capacity of other types can be calculated by multiplying the above figure by the number in the name. For example, for x16, the throughput in one direction is 2 x 16 \u003d 32 Gbps. Standard 2.0 was released in 2007, has throughput in one direction (doubled in two directions) for x1 - 4 Gbps. You can also calculate the bandwidth for other species. Standard 3.0 released in 2010, allows data transfer at a speed of 8 Gbps. The 4.0 standard is scheduled to be released by 2015 and will be twice as fast as 3.0.

Currently, the most common on motherboards are x16 for connecting video cards and x2 for connecting other devices.

USB bus (Universal Serial Bus) is designed to connect peripheral devices (for example, keyboard, mouse, joystick, printer, and others). Its mission is to connect various devices to a running computer, for example, toasters, keyboards, microwave ovens, LED lamps, fans, etc., without the need to install switches, jumpers, use software (drivers), etc.

First standard 1.0 appeared in 1994 and has a mode with low bandwidth of 1.5 Mbps (Low speed), with high bandwidth (Full-speed) up to 12 Mbps. The USB bus can operate in two modes: in low-speed mode, in which a keyboard, mouse, etc. work, with a low transmission speed (cable length - 5 meters) and high-speed mode (cable length - 3 meters), which allows you to work with maximum printer speed.

In version 1.1, the existing bugs were fixed.

In the standard 2.0 a new mode (Hi-speed) has appeared with a bandwidth of 25480 Mbps.

In this bus, you can connect devices, and the computer itself will determine the device that is connected. In this case, it is possible not only to connect a new device directly to the computer, but also to a device that is already connected to the computer. For example, you can connect a hard drive, microphone, and other devices to the keyboard.

It can use a hub that can connect up to 127 devices and supports Plug & Play technology. In this case, the bus automatically assigns a number to the devices with which it works. In addition to sending data, these wires also carry electricity, but in a small amount, which is enough for the keyboard, but may not be enough for the speakers. Therefore, speakers with high output power require a separate power supply.

The bus allows you to connect devices while the computer is on. When connected, they request the master device, which assigns them addresses, after which they can start working. In addition to data, electricity is also transmitted to power the devices. If the power supply is insufficient, the devices can be connected to an additional power source.

In addition to increasing the performance of the computer, the need for upgrading may arise when adding new devices, which requires the appropriate power supply capacity, a certain number and type of slots for expansion cards on the motherboard and the number of free bays inside the system unit. Over time, with the proliferation of the USB standard, many devices that can currently be connected are not located inside, but outside the system unit. Thus, more and more external devices will be produced and the number of connectors inside the case and bays will not be a problem when installing a large number of additional devices.

The latest standardUSB 3.0 appeared in 2008, the connectors are compatible with earlier standards. However, four more communication lines were added in the form of two twisted pairs and the cable itself became thicker. The connectors on the motherboard for connecting such cables are blue, and the plugs themselves have blue inserts. Thus, the maximum data transfer rate was increased to 4.8 Gbps, and the transfer rate increased to 600 MB per second (an indicator higher than that of the standardUSB 2.0 tenfold). At the same time, the transmitted current has increased from 500 mA to 900 mA, which makes it possible to connect more power-hungry devices.

Tire PCMCIA It is used in laptops and has the ability to transmit data over 16 bits with addressing up to 64 Megabytes, with a bus frequency of 33 megahertz. This bus allows you to connect different devices - hard drives, modems, memory expanders, etc. Many adapters are manufactured using the PnP technology and can connect devices without turning off the computer. All devices connected to this connector are energy-efficient. The bus has great prospects in the future and will be installed in desktop computers.

PCMCIA cards, also called PC cards, are designed for RAM, modems, hard drives, etc. devices and come in three types. They have a length and width of 85x54 mm, and the thickness depends on the type. Type I has a thickness of 3.3 mm, type II - 5 mm, type III - 10.5 mm. The card is inserted into a slot on the ISA bus adapted for these cards, also called PCMCIA.

Type I is used for RAM, sometimes for modems or a network card, has a 16-bit interface, thickness 3.3 mm, type II for the same devices, but they are thicker (5 mm), in type III you can also install a hard disk (thickness 10, 5 mm). The laptop has a compartment where you can install either one type I or II card, or in modern models - two type I and II cards or one type III.

For the modem, a special connector (X-jack) is installed at the end of the card to which a wire is connected, at the other end there is a telephone connector (RG11) for connecting to a telephone line. When installing, you just need to insert the card into the hole until it clicks, and in order to remove it, you need to press the adjacent key, and the card will pop out. PC Card AT is called the PCMCIA connector for connecting to notebook and desktop computers.

The Card Bus is a further development of the PC Card, which transfers data over a 32-bit interface (PCMCIA cards have become known as PC Cards). The bus connects the card to the video system, which allows you to bypass the ISA bus. This bus is called the Zoomed Video Port - a port of the enlarged video.

IEEE 1394 - developed by the Institute of Electrical and Electronics Engineers (IEEE) based on the Apple bus - Firewire in 1995, where the number 1394 denotes the serial number of the tire, which was developed by this organization. The bus allows you to connect up to 16 devices to one node, while each device is assigned a number that has a dimension of 16 bits, that is, more than 64,000 devices can be addressed in total. Up to 63 devices are connected to each bus, and each node is assigned a 6-bit number. 1023 buses can be connected to each other using bridges, each of which has a capacity of 10 bits, the bus is hot swappable. Each new device can be connected to any free port, on one device there are from one to three, but possibly up to 27. The only exception is the prohibition of device loops, since the bus supports a tree structure.

There are three classes of devices with data transmission 98.3; 196.6 and 339.2 Mbps, or they are usually rounded off to 100, 200, and 400 Mbps for IEEE 1394a and 800 and 1600 for IEEE 1394b. According to the IEEE 1394.1 standard, developed in 2004, you can connect up to 64 449 devices, according to the IEEE 1394c standard, developed in 2006, you can use an Ethernet cable. Moreover, the maximum cable length is up to 100 meters, and the speed is up to 800 Mbit / s.

There are three types of connectors: 4 pin - no power, installed on laptops and camcorders, (IEEE 1394a without power), 6 pin - with two additional pins for power(IEEE 1394a) and 9 pin with additional contacts for receiving and transmitting(IEEE 1394 b). Also can be RJ-45 connector(IEEE 1394c).

If the cable consists of 6 copper wires, two for power, the other two pairs are for data, with each pair shielded and also all wires shielded together. Since the power supply is from 8 to 40 volts at a current of up to 1.5 amperes, many devices do not require an additional connection to the network. Cables up to 4.5 meters can be installed between the two devices, the bus connectors are simple and easy to connect.

The bus operates in synchronous and asynchronous modes. Asynchronous transmission sends data organized in packets and retries if errors occur, which is important for accurate data transmission. Synchronous transmission is used in multimedia, for the transmission of audio and video data, but if the data is lost, then this is not critical, since the next portion of data is being transferred.

The IEEE 1394 bus transmits data in digital form, so the video quality is better than analog. A computer can programmatically turn on and off devices connected to it. The bus is independent of the computer, that is, it can work in the absence of a computer, for example, to transfer data from a video camera to a VCR. This bus is supported by Windows 98 (update required), Windows ME, Windows 2000, Windows XP and others.

To speed up the work was introduced host bus (sometimes called the processor bus). Designed for 64-bit data transfer between the processor, RAM and L2 cache and operates at 50, 60, 66, 75, 100, 133 MHz, while the PCI bus is at half frequency (25 ; 30; 33; 37.5 MHz).

Exploitation... If one of the old cards stops working, then you can try to remove it and clean the contacts with an ordinary eraser, which will remove deposits and oxide. After installation, check the operation of the board. Unused slots should preferably be covered with special covers.

Bus (Bus) is the entire set of lines (conductors on the motherboard) through which components and PC devices exchange information. Buses are designed to exchange information between two or more devices. A bus connecting only two devices is called port... In fig. 1 shows the structure of the bus.

The bus has places for connecting external devices - slotswhich as a result become part of the bus and can exchange information with all other devices connected to it.

Figure: 1. Bus structure

Tires in PC differ in their functional purpose :

• system bus (or CPU bus) is used by Cipset chips to send information to and from (see also Fig. 1);
• tire intended for information exchange between the CPU and the cache memory (see also Fig. 1);
• memory busused to exchange information between RAM and CPU;
• i / O busesinformation is divided into standard and local.

Local I / O bus Is a high-speed bus designed to exchange information between high-speed peripheral devices (video adapters, network cards, scanner cards, etc.) and the system bus under the control of the CPU. Currently, the PCI bus is used as the local bus. To accelerate video I / O and improve PC performance in 3D processing, Intel has developed the AGP bus ( AcceleratedGraphicsPort).

Standard I / O bus used to connect slower devices (for example, mice, keyboards, modems, old sound cards) to the buses listed above. Until recently, this bus was the ISA bus. Currently - USB bus.

The bus has its own architecture allowing to implement its most important properties - the possibility of parallel connection of an almost unlimited number of external devices and ensuring the exchange of information between them. Any bus architecture has the following components:

• lines for data exchange (data bus);
• lines for addressing data (address bus);
• data control lines (control bus);
• bus controller.

Controller The bus manages the data exchange processor and service signals and is usually performed as a separate microcircuit or as a compatible chipset - Chipset.

Data bus provides data exchange between the CPU, expansion cards installed in the slots, and RAM memory. The higher the bus width, the more data can be transferred per clock cycle and the higher the PC performance. Computers with the 80286 processor have a 16-bit data bus, those with the 80386 and 80486 CPUs have a 32-bit data bus, and computers with a Pentium-family CPU have a 64-bit data bus.

Address bus serves to specify the address to a PC device with which the CPU communicates. Each PC component, each I / O register and RAM cell has its own address and are included in the general address space of the PC. An identification code ( address) the sender and (or) the recipient of the data.

To speed up data exchange, an intermediate data storage device is used - rAM – RAM... The amount of data that can be temporarily stored in it plays a decisive role. Volume depends from the width of the address bus(number of lines) and thus from the maximum possible number of addresses generated by the processor on the address bus, i.e. on the number of RAM cells that can be assigned an address. The number of RAM cells should not exceed 2 n, where n - bit width of the address bus. Otherwise, some of the cells will not be used, since the processor will not be able to address them.

In the binary system, the maximum addressable memory size is 2 n, where n - number of lines of the bus address

The 8088 processor, for example, had 20 address lines and could thus address 1 MB of memory (2 20 \u003d 1,048,576 bytes \u003d 1,024 KB). In a PC with an 80286 processor, the address bus width was increased to 24 bits, and the 80486, Pentium, Pentium MMX and Pentium II processors already have a 32-bit address bus with which you can address 4 GB of memory.

Control bus transmits a number of service signals: write / read, readiness to receive / transmit data, acknowledge receipt of data, hardware interrupt, control, and others to ensure data transfer.

Main characteristics of the tire

Bus width determined by the number of parallel conductors included in it. The first ISA bus for the IBM PC was eight-bit, i.e. it could transmit 8 bits simultaneously. The system buses of modern PCs, such as the Pentium IV, are 64-bit.

Bandwidth tires is determined by the number of bytes of information transmitted over the bus per second.

When calculating the bandwidth, for example, the AGP bus, you should take into account its mode of operation: due to the doubling of the clock frequency of the video processor and the change in the data transfer protocol, it was possible to increase the bus bandwidth by two (2x mode) or four (4x mode) times, which is equivalent to increasing the bus clock frequency by the corresponding number of times (up to 133 and 266 MHz, respectively).

External devices are connected to the buses using interface (Interface - interfacing), which is a set of various characteristics of any PC peripheral device that determine the organization of information exchange between it and the central processor.

These characteristics include electrical and timing parameters, a set of control signals, communication protocol and design features of the connection. Data exchange between PC components is only possible if the interfaces of these components are compatible.

PC bus standards

The principle of IBM compatibility implies the standardization of the interfaces of individual PC components, which, in turn, determines the flexibility of the system as a whole, i.e. the ability to change the system configuration as needed and connect various peripheral devices. In case of incompatibility of interfaces, controllers are used. In addition, flexibility and system unification is achieved through the introduction of intermediate standard interfaces such as the interfaces required for the operation of the most important peripheral input and output devices.

System bus intended for the exchange of information between the CPU, memory and other devices included in the system. System buses include:

• GTL, 64-bit, 66, 100 and 133 MHz;
• EV6, the specification of which allows its clock frequency to be increased to 377 MHz.

Tires are improved in accordance with the development of PC peripherals. Table 2 shows the characteristics of some I / O buses.

TireISA was considered a PC standard for many years, however, it is still retained in some PCs along with the modern PCI bus. Intel has partnered with Microsoft to develop a phase-out strategy for the ISA bus. At the beginning, it is planned to exclude ISA connectors on the motherboard, and later exclude ISA slots and connect floppy drives, mice, keyboards, scanners to the USB bus, and hard drives, CD-ROM drives to the IEEE 1394 bus. However, there is a huge fleet of PCs with the ISA bus will be in demand for some time.

Tire EISA was a further development of the ISA bus in the direction of improving system performance and compatibility of its components. The bus did not become widespread due to its high cost and bandwidth, which was inferior to the bandwidth of the VESA bus that appeared on the market.

table 2. I / O Bus Specifications

Tire VESA , or VLB , is designed to connect the CPU with fast peripheral devices and is an extension of the ISA bus for exchanging video data.

Tire PCI was developed by Intel for the Pentium processor and is a completely new bus. The fundamental principle behind the PCI bus is the use of so-called bridges, which communicate between the PCI bus and other types of buses. The PCI bus implements the Bus Mastering principle, which implies the ability of an external device to control the bus when sending data (without the participation of the CPU). During the transfer of information, the device supporting Bus Mastering seizes the bus and becomes the master. In this case, the central processor is freed up for other tasks while data transfer is taking place. In modern

on motherboards, the PCI bus clock rate is set to half the system bus clock speed, i.e. at 66 MHz FSB, the PCI bus will operate at 33 MHz. The PCI bus has now become the de facto standard among I / O buses.

Tire AGP - a high-speed local I / O bus designed exclusively for the needs of the video system. It connects the video adapter (3D accelerator) to the PC memory system. The AGP bus was developed based on the PCI bus architecture, so it is also 32-bit. However, at the same time it has additional opportunities to increase the throughput, in particular, through the use of higher clock frequencies.

Tire USB was developed by the leaders of the computer and telecommunications industry Compaq, DEC, IBM, Intel, Microsoft for connecting peripheral devices outside the PC case. The speed of information exchange via the USB bus is 12 Mbit / s or 15 Mbyte / s. To computers equipped with a USB bus, you can connect peripheral devices such as a keyboard, mouse, joystick, printer without turning off the power. All peripheral devices must be equipped with USB connectors and be connected to a PC through a separate external unit called USB hub , or hub , with which you can connect up to 127 peripheral devices to your PC. The USB bus architecture is shown in Fig. 4.

Tire SCSI (SmallComputerSystemInterface) provides a data transfer rate of up to 320 MB / s and provides for connection to one adapter up to eight devices: hard drives, CD-ROM drives, scanners, photo and video cameras. A distinctive feature of the SCSI bus is that it is a cable loop. With PC buses (ISA or PCI), the SCSI bus is connected via host adapter (HostAdapter). Each device connected to the SCSI bus can initiate communication with other devices.

Tire IEEE 1394 – is a high-speed local serial bus standard developed by Apple and Texas Instruments. The IEEE 1394 bus is designed to exchange digital information between

PCs and other electronic devices, especially for connecting hard drives and audio and video processing devices, as well as for running multimedia applications. It is capable of transferring data at speeds of up to 1600 MB / s, working simultaneously with several devices transmitting data at different speeds, like SCSI.

Almost any device capable of working with SCSI can be connected to a computer via the IEEE 1394 interface. These include all kinds of disk drives, including hard drives, optical drives, CD-ROMs, DVDs, digital camcorders, devices. Thanks to such wide possibilities, this bus has become the most promising for combining computers with consumer electronics. IEEE 1394 adapters for the PCI bus are already being released.

Personal computer bus

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