Motherboard 101

Learn all about the parts of a motherboard.




In oversimplistic terms, think of the motherboard as the skeleton of your computer. It provides the structure for all of the components -- processor, hard drive, RAM, graphics card, CD-ROM, sound card, keyboard, mouse, and so on -- and allows them to work together as the computer you know.

Identifying the parts of a motherboard is tough, even for professionals. Often you can't definitively identify them, only deduce their type by size and location. Here are some clues:


Central processor, or CPU

The easiest chip to identify is the largest chip on the motherboard. That's the central processor. It should have a ceramic heat sink glued to it. If there's not a heat sink glued to it, you can actually look at the chip and see what it is. Look for numbers or words such as 80486, Pentium, Pentium III, and K6. You may or may not find numbers that give you an idea of the chip's clock speed.


If you remove the processor, you will find a slot that seats the processor. The two most common processor slots are called slot and socket.

The connector for a slot processor looks like, well, a slot. Slot processors are encased in Single Edge Contact cartridges.

A socket connector uses a square processor that has dozens of pins on its underside.


Chip set

The chip set is also referred to as the bridge chips, the logic chips, or the glued chips. Nowadays, on most modern motherboards, the chip set is a single chip. If the motherboard is more than a couple years old, it might be two chips. Sometimes the chip set is labeled Intel, VIA, SIS, or ALI. The chip set contains controllers for the memory, the PCI bus, and your peripheral cards, among other things.


Cache RAM

Often the hardest chips to find on the motherboard are the cache RAM chips. They are usually soldered into the motherboard. They're often quite small and not obviously memory chips. Look around for small microprocessors. There may be two or four or six -- not very many.


RAM chips

There are two ways of attaching chips to circuit boards: surface mounting, which means that the chip is soldered right onto the board; and socketed, which means a chip socket is soldered into the board and a chip is inserted into the socket.


The RAM chips are rarely attached to the motherboard directly. They're almost always in RAM sockets -- usually perpendicular to the motherboard on smaller circuit boards called sticks. SIMM sticks or DIMM sticks are small green circuit boards with chips attached.


Motherboard 101: Slots

The PC world has three industry-standard slot form factors. (Macintosh currently has one.) Different slot form factors evolved with the development of the PC. As time and technology progressed, slot formats changed.


ISA

The first (and second most common) slot is the industry standard architecture (ISA) slot. These come in 8-bit and 16-bit varieties.


The 8-bit slot originated with the IBM PC. It runs at 8.3 MHz with a maximum transfer rate of 7.9 MBps.


The 16-bit slot was introduced with the IBM AT. It runs at 15.9 MHz with a maximum transfer rate of 15.9 MBps. The 16-bit slot is backward compatible with the 8-bit slot. This means you can run 8-bit ISA hardware on a 16-bit ISA slot.


All ISA slots today are 16-bit. They are the longest slots, and they reside at the end of the motherboard. They are black and are segmented in two. The segment touching the rear of the board is the 8-bit slot. The segment above the 8-bit slot is the 16-bit extension slot. An 8-bit card uses only the 8-bit segment. A 16-bit card uses both segments. ISA slots are a holdover from earlier PC designs and are being phased out.


Most modern PCs have two or three ISA slots on a motherboard.


PCI

The peripheral component interconnect (PCI) slot sits alongside the ISA slot. (It's usually a white connector.) It is theoretically a 64-bit connector running at 66 MHz with a maximum throughput of 508.6 MBps. But when implemented, PCI is a 32-bit connector running at 33 MHz with a maximum throughput of 127.2 MBps.


PCI offers many advantages over ISA slots in terms of speed and bandwidth. It has bus-mastering ability, allowing cards to talk directly to each other without going through the CPU. These features make PCI such a popular and widespread standard.


Most modern PCs have four or five PCI slots on a motherboard. Macs usually have four PCI slots. (Old Macs use NuBus slots.)


AGP

The advanced graphics port (AGP) is a single, light-brown slot. Intel designed AGP in response to the expanding 3D graphics-board market and the demand for memory to store texture maps.


AGP provides a high-speed dedicated connection for video. In addition to providing a faster and larger bandwidth, it allows the video card to use system memory.


In its current guise, AGP x2 is 32-bit running at 66 MHz, with a maximum throughput of 508.6 MBps. The next implementation of AGP, AGP x4, would offer an increase in speed to 132 MHz and increase throughput to more than 1,000 MBps.


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