PC Motherboard Specs and Guide

PC Motherboard Spec and Guide

A system boards may also be called a planar board, motherboard or main board. There are various types of system boards that differ depending on the type of case that they fit in and the type of processor that they host. The form factor of the motherboard describes its general shape, what sorts of cases and power supplies it can use and its physical layout. A company can make 2 motherboards that have basically the same functionality but that use a different form factor and the only real differences will be the physical layout of the board and the position of the components. Common form factors include AT, Baby AT, ATX, Mini ATX, LPX, Mini LPX and NLX. The table below contains more information:

Style	Where Found	Match to Case and Power Supply
Full AT	Very Old PCs	Full AT, Full Tower
Baby AT	Older PCs	All but Slimline, ATX
ATX	Newer PCs	ATX
Mini ATX	Newer PCs	ATX
LPX	Older Retail PCs	Slimline
Mini LPX	Older Retail PCs	Slimline
NLX	Newer Retail PCs	Slimline

NOTE: Laptop motherboards tend to be proprietary to the model for which they are designed. Below is a graphic that shows some of the common features of motherboards. Note that these will vary from board to board depending on the form factor.

ATX System Board

System Boards typically have several components that are replaceable/upgradeable as follows:

Processor - Upgrading the processor is a fairly simple process. Make sure that the new processor is supported by the motherboard.
Memory(RAM) - Before upgrading memory, check the motherboard manual for specifications on supported memory types and speeds.
CMOS Battery - These batteries are designed to last 2 to 5 years. Failure of this battery can result in an error code, however, the most noticeable symptom is the computer's lack of ability to keep proper time.
BIOS ICs - Newer BIOS chips are "Flash" upgradeable using software. Older BIOSes require replacement of the BIOS ROM chip. Before upgrading, make sure that your processor is compatible with the BIOS and motherboard chipset.
Cache Memory - On some system boards, the cache memory can be upgraded. It may be as simple as adding an IC to an open slot. Other times, you may have to remove the existing one to upgrade.

Motherboards also contain configurable jumpers and possibly even DIP switches(typically on older models). Jumpers use BERG pins and a small connector that slides onto the pins to designate "on". BERG connectors are also used to connect the front panel LEDs and switches to the board.

The back of the motherboard contains ports used for connecting various peripherals. Peripherals are composed of input and output devices including the mouse, keyboard, monitor, speakers, printer, etc. So what is the difference between an input device and an output device? It is just as the name says. The mouse and keyboard are input devices since they are used to provide the computer with information. Output devices provide YOU with information such as speakers, printers and the monitor. Older PC-XT and AT board typically had a 5 pin DIN keyboard connection. The newer ATX style uses the smaller 6 pin mini DIN connection.

Expansion Busses:

Bus	Format	Notes
PC-bus	8 Bit	Used in PC and PC-AT models
ISA	16 bit	Runs at 8 or 8.33mhz
VESA	32 bit	Designed to address video limitations
EISA	32 bit	Supports Plug-and-Play and Bus mastering
MCA	32 bit	Supports PnP and Bus mastering
PCI	32 bit	Supports PnP, Burst Mode, Bus Mastering. Utilizes the host bridge to communicate with other types of expansion slots.
AGP	32/64 bit	Variation of PCI designed to handle 3D graphics better from video cards.

Most modern motherboards contain AGP, PCI and ISA slots.

On newer and faster buses, a great deal of information is flowing through the channel every second. Normally, the processor is required to control the transfer of this information. Bus mastering involves having capable devices take control of the bus and do the work themselves instead of utilizing the CPU.

Plug-and-Play(PnP) - Compatible BIOSes can autodetect devices and assign resources to them. Non PnP compatible devices are configured first followed by PnP devices.

The IRQ(interrupt request) value is an assigned location where the computer can expect a particular device to interrupt it when the device sends the computer signals about its operation. Below is a list of common IRQ settings.

IRQ	Device
IRQ 0	System Timer
IRQ 1	Keyboard
IRQ 2/9	Video Card
IRQ 3	Open unless needed for Com 2 or 4
IRQ 4	Com 1, Com 3
IRQ 5	Open unless needed for LPT2 or sound card
IRQ 6	Floppy Disk Controller
IRQ 7	LPT1(parallel port)
IRQ 8	Real time clock
IRQ 9/2	linked to IRQ 2
IRQ 10	Open
IRQ 11	USB
IRQ 12	PS/2 Mouse
IRQ 13	Math Co-processor
IRQ 14	Hard Disk Controller
IRQ 15	Open

Input/output(I/O) addresses are resources used by virtually every device in a computer and represent locations in memory that are designated for use by various devices to exchange information between themselves and the rest of the PC. The following is a list of common I/O settings.

1FO-1F8 - Hard Drive Controller, 16-bit ISA
220 - Soundcard
278-27F - LPT2
2F8-2FF - COM2
320-32F - Hard Drive Controller, 8-bit ISA
378-37F - LPT1
3D0-3DF - Video Adapter
3F0-3F7 - Floppy Controller
3F8-3FF - COM1

Universal Serial Bus(USB) - A high-speed I/O bus that supports the daisy chaining of devices(up to 127). USB hubs are used to provide connections for multiple devices. USB supports the addition and removal of devices while they are on(hot-swapping). Devices are either full speed or low speed. Full speed device cabling can be up to 16 feet 5 inches(5 meters) in length. Low speed cabling is limited to 9 feet 10 inches(3 meters). USB supports Isochronous transfers that can stream data such as voice or video

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