The device and principles of operation of the motherboard

The motherboard device includes the following nodes:

1) the central link of the entire computer system is the processor. To install it on the motherboard, a special socket is used – a socket. Each socket differs from each other constructively, is designed for certain processors and is indicated by a three-digit number.

2) One of the important devices that is located on the motherboard is the BIOS chip. It contains the boot program for the computer and its configuration. When you turn on the computer’s power, the BIOS initializes the devices that are connected to the motherboard and checks their performance. And if everything is fine, then the bootloader is searched for on storage media. Modern motherboards may have two BIOS chips to improve system reliability.

3) The second of the most important devices on the motherboard is the chipset, it is a set of chips, which are functionally divided into north and south bridges, which are responsible for the connection of the processor, memory and video card and the connection of slow devices such as a hard drive, network card , sound card, etc. In addition, the north bridge communicates with the devices included in the south bridge with the processor. Usually, two bridges are made in the form of two separate microcircuits, and the north bridge, due to heating in operation, can be supplied with a cooling system.

4) Removable slots of the operating board are located on the system board. They are usually located near the processor socket and the northbridge chip. The number of slots can be different (from 2 to 6). These slots are connected by buses to the sulfur bridge and through it to the CPU (central processing unit).

5) Next to the north bridge, perpendicular to the RAM slots, there is a connector for a video card. In older computers, the connector was of the AGP type, in modern boards it is a PCI-Express x16 connector. Like the slots on the operating board, this connector is connected via a bus to the northbridge chip.

6) Just below the video card connector, in parallel, there are PCI connectors. They are designed to connect internal devices such as: sound cards, cards of various tuners, network cards, etc. An optional PCI Express x1 slot can also be located before these ports.

7) On the motherboard there are pin connectors for connecting hard drives and optical drives with an IDE interface, as well as newer SATA connectors. Modern motherboards may not have IDE connectors (usually 1-2 connectors).

8) Small microcircuits can be located next to the SATA connectors – these are SATA controllers. The main task of the SATA controller is to create RAID arrays of hard drives.

9) The BIOS battery is located on the system board, which serves to constantly power the microcircuit, the energy of the battery is used to store temporary information to the CMOS memory.

10) The motherboard may have connectors for connecting USB ports, for example, from the front panel.

11) On the system board there are pin connectors for connecting the buttons on the front panel of the system unit: power on, reboot, indicator of hard drive operation and power on, speaker connection.

12) In modern motherboards, sound is often supported by an audio codec chip (built-in sound card). In this case, the function of the sound processor is performed by the southbridge chip.

13) Each modern board has a built-in network controller that ensures the operation of a PC in a local network. Most often, this computer is used to interact with the network has an RJ-45 port (used to connect a twisted pair cable).

14) There is a pin jumper (jumper) on the motherboard for resetting the BIOS, that is, resetting user settings to factory settings.

15) To power the motherboard and its components, as well as devices connected to it, there is a 24-pin connector to which the power supply unit (PSU) is connected.

16) On any motherboard there is a panel with ports placed on it: 1) PS / 2 – for connecting a keyboard / mouse; 2) LPT – connection of old printers, scanners and the like; 3) connectors for connecting audio devices; 4) RJ-45 connector; 5) USB ports – a universal port for connecting external devices; 6) if there is a built-in video card, there may be ports (VGA, DVI, HDMI); 7) S / PDIF – connector provides connection of digital audio outputs for external audio systems that support digital optical technologies; 8) IEEE 1394a – used by high-speed external devices (multimedia).

BIOS chip

BIOS stands for Basic Input/Output System. It is a key element of the motherboard, without which all its components are just a set of pieces of iron. The BIOS, using the tools provided by the chipset, manages all the components and resources of the motherboard. It follows that the BIOS version used is largely dependent on the chipset. In addition, the microcircuit must contain the data and features of the components used. The BIOS code is stored in a non-volatile read-only memory (ROM BIOS) or flash memory chip. On modern motherboards, the second type of memory is mainly used. BIOS chips are marked with an alphanumeric code: 28F… – 12V flash memory; 29C… – 5V flash memory; 29LV… – flash memory 3V; 28Cxxx – EEPROM; 27Сxxx – EPROM memory, recorded using a special device – a programmer, erased with ultraviolet light. Modern BIOS chips are built on flash memory and can be overwritten using special utilities.

CMOS memory

The CMOS memory, combined with the timer clock, is the computer’s non-volatile configuration memory. In addition to standard purpose cells, the CMOS memory contains cells that are used to store the current chipset parameters set by the built-in CMOS Setup utility. A lithium battery is installed on the system board to power this memory. It is designed to last for several years. The first sign that you need to replace it may be that the internal clock of the calendar stops when you turn off the computer. The CMOS memory is an important part of the computer, and the correct power supply can significantly affect the performance of the computer as a whole.

CMOS Setup Options

The CMOS chip must contain information about installed system disks and selected user options before using the computer. The Setup program allows you to select the required options. This program is launched by pressing a certain key or key combination at the beginning of the POST procedure. In different BIOS versions, loading is carried out with different keys (Delete, F2,). You can usually find information about the keyboard shortcut on the motherboard documentation, and it is also written on the screen (usually on the bottom line). After starting the program, a menu screen appears on the screen. In most modern BIOS Setup programs, the main menu consists of the following items: 1)Maitenance – determining the operating frequency of the processor and deleting passwords; 2) Main (main parameters) – distribution of hardware resources;

3) Advanced (additional parameters) – setting additional properties;

4) Security (security) – setting passwords and activating other security tools;

5) Power (power) – setting power management parameters;

6) Boot (boot) – definition of boot parameters and power supply;

7) Exit (exit) – usually with saving or canceling the set parameters.

Personal computer processor

In a PC device, the CPU (central processing unit) is responsible for computing and processing all information. The processor is a complex high-tech product, in which the number of different elements (mainly transistors) counts for more than a billion.

The general architecture of the processor can be represented as the following main blocks: 1) control device – designed to decrypt and execute commands;

2) working registers – elements necessary for addressing memory and performing computational operations;

3) arithmetic-logical unit – performs logical and arithmetic operations;

4) input-output control – the organization of data input-output to the processor or from the processor.

The processor works with commands. Each instruction specifies what action the processor is to perform and on what data. Any program that is executed by the processor consists of many different instructions, by executing which the processor executes the program. In general, the command for the processor is:

Operation code – Operand1 – … – Operand2.

Operation code Operand1 Operand2

Thus, each command at the lowest level is a group of bits (zeros and ones), which in turn forms the above fields (figure). The opcode indicates what the processor should do, and the operand fields provide the necessary data to perform the processor’s operation.

The processor works with random access memory, since it stores the data necessary for the processor to work, and the processor places the results of its calculations in random access memory before final storage in long-term memory (on a hard disk, etc.). The interaction of the processor with memory occurs through the bus address, data and control.

On the address bus is placed the address of the memory cell with the data needed by the processor.

The data bus contains data from the processor that needs to be written to memory, or data from memory that the processor needs to perform calculations.

The control bus receives signals from the processor that tell the memory or other devices what the processor will work with and what operation it will perform. The processor works according to the following algorithm. The software counter outputs the address of the instruction on the address bus. The memory puts the instruction at this address on the data bus. The processor enters an instruction into its instruction register. There the command is decrypted, the operation code is determined, the length of the command in bytes is determined. The program counter addresses the next instruction, located at an instruction length away from the previous one. The command itself, after it is processed by the command register, is executed by the rest of the processor devices. When the instruction completes, the contents of the program counter are placed on the address bus and the loop repeats.

The processor executes all commands sequentially, command by command. Sometimes the execution of a command needs to be stopped, because it is necessary to execute a higher priority. For this, special transition commands (interrupts) are developed. When such commands appear, current operations are stopped, the last state of the processor is remembered, then the necessary command is executed. After its execution, the last state of the processor is loaded and the command queue continues to be executed.

How many bits are processed by the processor at a time (in one cycle) is shown by such a characteristic as the processor bit depth. At the moment, most processors are capable of processing from 32 to 64 bits in one cycle. The clock principle is the basis of the processor operation. The execution of each command takes a certain number of cycles. In a PC, clock pulses are set by one of the microcircuits included in the chipset located on the motherboard. The higher the frequency of clocks received by the processor, the more commands it can execute per unit of time, and the higher its performance.

The performance of the CPU is also affected by the size of the cache, the number of cores, and the chipset located on the motherboard.

Multi-core processors are processors with 2 or more cores located in the same package, as a result of which information processing is carried out in several threads, which ultimately affects performance.

The processor works much faster than the RAM, and when accessing it, it has to wait for a result for some time. To reduce latency, a small amount of very fast memory called cache memory is installed directly on the processor chip. It contains the data most frequently used by the processor and usually runs at its clock speed. Special algorithms for cache memory allows you to timely load the data needed by the processor from RAM, which increases system performance.

Modern processors have a two- or three-level cache organization. Level 1 cache memory has the highest speed and small size (no more than 100 kb), level 2 cache memory has a slightly slower performance, but its volume can range from several hundred KB to several MB. Level 3 cache is also slower than Level 1 cache and is typically over MB in size.

The CPU core operates at a clock frequency that is the product of the FSB frequency and the multiplier (processor multiplier). FSB – processor external bus frequency.

Processor sockets

Throughout the history of PC development, two types of sockets for processors have been distinguished: 1) sockets – the most common type of sockets (square shape);

2) slots – an outdated type of connectors, outwardly similar to connectors for connecting expansion cards.

There are currently two processor manufacturers: Intel and AMD.

Intel CPU Sockets: 1)Desktop (Socket37, Socket423, Socket478, SocketT(LGA775), SocketB(LGA1366), SocketH(LGA1156), SocketH2(LGA1155), SocketB2(LGA1356), SocketR(LGA2011), etc.)

2)Mobile: Socket495, Socket479, Socket441, SocketM, SocketP.

3) Server: Socket8, PAC418, Socket603, Socket604, PAC611, SocketJ(LGA771), SocketB, SocketH, SocketTW(LGA1248), SocketLS(LGA1567).

AMD CPU Sockets: 1) Desktop: SocketA (Socket462), Socket754, Socket940, Socket939, SocketAM2, SocketF(Socket1207), SocketAM+, SocketAM3, SocketAM3+, SocketFM1, SocketFM2.

2) Mobile: SocketA, Socket754, Socket563, SocketS1, SocketFS1, SocketFP1, FT31

3) server: SocketA, 940, SocketF, SocketF+, SocketG34, SocketC32.


Random access memory (RAM / RAM) – is used for the rapid exchange of information (commands or data) between the processor, external memory and peripheral devices. From English. this type of memory is translated as random access memory. Random access implies the ability to write to any RAM cell or read any RAM cell in random order. At the moment, there are two types of RAM: static and dynamic. The difference between them lies in the fact that in static RAM, the signals on the capacitors are maintained constantly, in dynamic RAM, the charge on the capacitors is regenerated (approximately every 18 μS) using a special signal. In this regard, SRAM chips are more productive, but they have larger overall dimensions. DRAM chips are slower, but they have a higher packing density, which means that more memory can fit on a single printed circuit board.

Different types of memory have found different uses in PCs. Faster static memory is used in the processor cache. Dynamic types of memory are used as a buffer memory of various devices, as well as the main RAM. At the moment, the most common type of dynamic RAM is SDRAM memory, and its varieties DDR1, DDR2, DDR3, DDR5 (in video adapters).

Structure of dynamic memory

Dynamic memory got its name from the principle of operation and its storage cells, which are made in the form of capacitors formed by elements of semiconductor microcircuits. When a logical 1 is written to a cell, the capacitor is charged; when a 0 is written, it is discharged. The reading circuit discharges this capacitor through itself, and if the charge was not zero, it sets its output to a single value and recharges the capacitor to its previous level. If the cell is not accessed, over time, due to leakage currents, the capacitor is discharged and information is lost. In this regard, such a memory requires constant periodic recharging of capacitors, that is, the memory can operate in a dynamic mode (constant access to each memory cell is required).

Due to the relative simplicity of dynamic memory cells, millions of cells can be placed on a single chip and the cheapest semiconductor memory of sufficiently high performance with moderate power consumption is obtained.

RAM also differs in the types of modules. All RAM modules are standardized and mutually compatible. There are two types of modules: SIMM, DIMM. Each of these modules is also divided by the number of tracks. At the moment, DIMM modules with two hundred and forty contact plates are used.

In addition, RAM modules also differ in the presence and location of keys.


Older memory modules had two keys. DDR2, DDR3 memory has only one key, but it is located at different distances from the edge. In this regard, DDR2, DDR3 memory modules are not compatible.



The keyboard is a PC peripheral that allows you to enter information using special buttons. The electronic part of the keyboard can be represented as the following block diagram


Sync Buffer
Key field


Key polling scheme

Sync +5V Ground

Regardless of the types of keypress sensors used, they are all combined into a matrix – a keypad. The keyboard contains an internal controller (microprocessor) that performs key matrix scanning, indicator control, internal diagnostics and communication with the motherboard.

The internal keyboard controller is capable of detecting whether keys have been pressed or released. When a key is pressed, the keyboard transmits a scan code identifying it. When the key is held down, after a while the keyboard starts auto-repeat of the scan code transmission. Also, the scan code is transmitted when the key is pressed. By itself, the scan code is a sequence of bits, which is a number that identifies the location of the key in the keyboard field.

During the operation of the keyboard, the microprocessor constantly scans the key field for pressing / releasing keys. If the key is pressed, the microprocessor generates the corresponding scan code. This scan code is then transmitted over the interface to the motherboard to the keyboard/mouse controller. If the interface is busy, the information is buffered……….

Membrane keyboards are currently widely used in portable devices. This keyboard is a variation of the previous one, but it does not have separate keys. The contacts are located on the printed circuit board, a rubber cap is installed above them, all this is a single design. A key is installed above each membrane. When pressed, the key pushes the membrane inward and it closes the contacts. When the key is released, the membrane returns to its original position. Such keyboards are not suitable for long-term typing, since the keys have a hard travel. However, due to the fact that this type of keyboard has a minimum of details, therefore it is considered quite safe in terms of fault tolerance. In addition, these keyboards are the cheapest.

As non-contact keyboards, keyboards with capacitive sensors went into production. Such keyboards are more expensive than contact keyboards, but they are more resistant to dirt and corrosion.

Capacitive sensors do not have NO contacts. Their role is played by two plates that are embarrassed relative to each other and a special circuit that reacts to a change in capacitance between them. The keyboard is a set of such sensors. Thanks to non-contact sensors, such a keyboard is resistant to corrosion and dirt, it practically does not rattle (a phenomenon when a character is displayed several times with one keystroke). In addition, this type of keyboard is the most durable. The only drawback of such a keyboard is the high cost.

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