The motherboard is the main printed circuit board in a computer. It contains the CPU, appropriate support chips, device controllers, memory and also expansion slots to give success to the computer’s internal bus. The motherboard is the heart of the system. It is called mother board because all other features and peripherals plug into it to operate. Let’s know detail about components of motherboard.
Components of motherboard
Picture given below presents the contents of a typical PCI / ISA motherboard. Some of its major components are described below.
Microprocessor and upgrade socket
Most systems do not solder the microprocessor permanently to the motherboard. The processor is in a socket that permits the processor’s easy removal from the motherboard.
The socket is generally designed to support several types of microprocessors. This enables a system to be upgraded in the future with more powerful processor by simply replacing the older with a better one.
Cache memory and DRAM controller
The main memory DRAM (dynamic RAM) is physically packaged on small circuit boards called SIMM or DIMM. SIMM stands for Single In-line Memory Module and DIMM stands for Dual IN-line Memory Module. The DRAM SIMMs are installed in SIMM socket on motherboards.
For timing, interface and refresh of DRAM, a DRAM controller device is needed between the local bus and the DRAM chips.
The main system memory (DRAM) cannot keep up with the performance of the processor and becomes a performance bottleneck. To overcome this limitation, a second smaller memory, called cache memory, is placed between the microprocessor and the system memory.
This memory (SRAM) is much faster and can keep up with the processor’s performance. The circuits that manage the cache memory is called the cache controller. The DRAM controller and cache controller functions are typically in a single chip on the motherboard.
The high-speed cache memory is also on the motherboard and can be expanded is size by adding chips into empty sockets on the motherboard.
PCI bus bridge chip
This chip converts the microprocessor’s local bus to the PCI bus. This chip is different for different microprocessors. In modern microcomputers the “core logic” chip set includes the microprocessor.
In modern microcomputers the “core logic” chip set includes the microprocessor local bus to PCI bride chip, the system memory controller and cache controller chip and the PCI to ISA bridge chip.
Keyboard / Mouse controller and Ports
A motherboard generally contains a keyboard is attached to the motherboard through a serial interface cable. The keyboard is attached to eth mother board through a serial interface cable.
The keyboard clock and data interface signals attach to a micro-controller chip on the motherboard. This chip in turn attaches to the main microprocessor bus.
The micro controller does no tactually send keyboard character codes, it actually sends special 8-bit scan codes, that are translated by the system unit’s software to character codes.
BIOS stands for Basic Input/Output System. The ROM BIOS is a read only memory that contains software. Its primary purpose is to load the basic operating system software form the system’s boot or start up device and perform power on system tests.
The operating system boot device is usually the system’s hard disk or the LAN port. The read only memory is about 128KB in size. Most of the times its contents are moved to faster DRAM memory for execution.
Some BIOS also incorporates features to support system configuration, detection and resource allocation as defined by the new plug and play specifications.
Real-time Clock and calendar
Every motherboard contains a chip called a real-time clock/calendar. This device also contains a small nonvolatile memory (normally 64 bytes). This device always runs even when the system is powered off. The power is supplied by a small battery installed on the motherboard.
This device supplies data and time to the operating system and stores basic system configuration data in the nonvolatile memory. Loss of this data by disconnection of the battery or a low battery condition temporarily cripples the system by destroying key information for configuration.
PCI to ISA Bridge
The PCI motherboard contains a bridge chip. This chip performs transformation of the PCI bus to the older ISA bus. This chip contains the Intel core logic including DMA chips or their equivalents.
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