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A motherboard is the central printed circuit board (PCB) in almost all computers by holding important components of the system and provides linkage for other peripherals. The purpose of a motherboard is to provide a platform for these components to communicate each other.
The motherboard is also called planar board, system board or logic board. Modern motherboards may contain sockets for one or more microprocessors to be installed , slots for main memory modules (typically DIMM modules that contain DRAM chips) , a chipset that acts as an interface between CPU's front side bus , primary memory and other peripheral buses , non-volatile memory chips containing firmware or BIOS , a clock generator , expansion card slots and power supply connectors. In modern computers, some peripherals can be integrated directly into the motherboard such as modem. Form factors of motherboards like AT, ATX or mini-ATX depend on the size and shape of the motherboard and placement of its components.
Fig (1.1) Motherboard
The function of power supply is to provide electrical power for every component inside the system unit to operate reliably including its expansion slots through the system board power connectors by converting AC voltage from the outlet to DC voltage required by the computer circuitry.
AT-compatible power supplies have two six-wire bundles, marked as P8 and P9 designed to plug into the system board's P1 and P2 power plugs respectively. Reverse attachment can cause severe damage. The ATX system board connector is a 20-pin keyed connector so that it cannot be wrongly installed into the board. Power supplies also include fans to cool the system unit.
Fig (1.2) Power Supply
CPU stands for central processing unit or microprocessor. It is the major component of every system board and can be referred as "brains" of the system. Its purpose is to read, interpret and execute software instructions and also to carry out arithmetic and logical operations for the system.
Microprocessors commonly have two kinds of mounting methods, Single Edge Cartridges (SEC) and Zero Insertion Force (ZIF) sockets. Pentium microprocessors are available in a number of speed ratings and they generate a considerable amount of heat. So, microprocessors require heat sinks and cooling systems to dissipate the heat.
Fig (1.3) Microprocessor
There are three types of memory found on a system board, (i) ROM BIOS ICs (ii) RAM and (iii) cache memory. The function of memory modules is to provide a place to store information temporarily for the PC while other pieces of information are being processed.
The purpose of RAM is to operate directly with the microprocessor and can be read and written as desired. RAM is volatile type of memory. Modern system boards typically provide two or more DIMM sockets for small piggy-back memory modules containing various combinations of RAM devices. Earlier AT-boards employed SIMMs or combined several SIMM sockets with a DIMM socket.
Each system board contains ROM ICs that hold BIOS program that contains basic instructions for communications between microprocessor and various I/O devices. ROM is non-volatile form of memory. New ROM chips can be rewritten with new BIOS information that still remains after the power is removed. In older systems, the information in the ROM chips can only be changed by replacing the chip.
Fig (1.4) RAM and ROM chips
Secondary memory systems or storage devices have to function as mainstays of mass storage area of information.
Storage devices store binary information in the form of magnetic charges on moving magnetic surfaces or optical storage methods. Major storage devices are hard disks, floppy disks and tapes. The structure of magnetic disk is normally defined by tracks, sectors and heads. In a PC-compatible system, each sector holds 512 bytes of data.
Fig (1.5) Hard Disk Drive
The most widely used display device for most PCs is the VGA color monitor. The function of monitors is to display alphanumeric characters and graphics processed by the system unit on a screen.
Two popular types of monitors are Cathode Ray Tube (CRT) monitors and Liquid Crystal Display (LCD) monitors. LCD displays are relatively thin, flat, and lightweight, and require much less power to operate. They also offer better reliability and longer life than CRT monitors.
Other popular display output devices after monitors are printers. They convert text and graphical data from the computer to produce hard-copy output on a page.
Fig (1.6) CRT and LCD monitors
Adaptor cards that plug into the expansion slots of the system board are used to communicate expansion devices with the basic system. They typically contain interfacing and controller circuitry for the peripheral. Some adaptor cards include the entire peripheral. Typical adaptor cards are video adaptor cards, modems, LAN cards and sound cards.
Fig (1.7) Video adaptor and sound cards
Ports offer standard hardware connection and logical interface schemes that permit I/O devices to link with the system.
Characteristics of the ports differ on which I/O device they are to be connected such as 25-pin female port for printers, 15-pin female port for monitors, 6-pin mini-DIN port for mice and so forth.
System unit case
The function of the system unit case is to protect the inner components from physical or accidental harm of the surroundings. It is usually metal chassis and removable cover. Characteristics to adapt the system for different environments include mounting methods, ventilation characteristics, total drive capacity, amount of desk space and portability. Three types of PC case designs are (i) Desktops (ii) Towers and (iii) Portables.
(1.2) Names , Purposes and Performance Characteristics of Standardised Peripheral Ports
Port , Cabling And Connectors
-to effect an interface between the PC and a serial device such as modem
-can send data bits synchronously or asynchronously for a distance more than 10 feet between PC and a peripheral
-to connect printers and other parallel devices to the PC
-enables the computer to pass information to the printer at 8 bits at a time across eight data lines
-DB 25 port
-to link and work with peripheral devices such as keyboards , mice , hubs , modems , printers and so on
-also acts as an power cord for PDAs , smart phones and video game consoles
-permits data transmission rate of 480Mbps
-USB 2.0 port
-USB 2.0 cable
-USB Mass Storage ( e.g , flash drives )
-serial bus interface standard to permit data transmission
and used in digital audio , digital video , automotive and aeronautics applications
-supports both PnP and hot-swapping of components
-firewire can also be used for add-hoc computer networks
-permits data transmission speeds of 800Mbps and greater
-to act as network , computer video output , game controller port and some communications port
-do not possess plug and play function
-high-density and can easily be bent or broken
-due to its size and cost , DB connectors have been replaced by physically much simpler and cheaper USB , Firewire , SATA or Ethernet ports
Left - DE9M
Right - DB25F
-networking interface that communicates between PC's NIC and the rest of the network
- used for Ethernet connections on PCs and other Ethernet networking devices like routers , switches modems and other devices which support Ethernet interface
-circular connectors for analog audio signals
-also used in analog video applications and for digital interfaces like MIDI , IBM PS/2 Mouse or Keyboard
-DIN connectors are no longer in use and replaced with standard ICE 60130-9
-5pin DIN 180ÌŠ
-multi-pin electrical connectors used in various applications
-9.5 mm diameter with pins from three to nine
-drastically different from each other with no simultaneously and directly overlapping similarities
(PS/2 Keyboard and Mouse)
-6pin mini-DIN cable
-acts as an interface for parallel printers and other devices to a computer
- called for the busy lead to toggle with each received line of data (busy by line)
-Centronics interface was superseded by IEEE 1284