 Put simply, a computer consists of a microprocessor that does the "thinking" (just mathematical calculations, really), data storage devices that hold the information the microprocessor needs, and a monitor, keyboard, and mouse that let you tell the processor what to "think" about next. The large circuit board that connects all of these things together in your PC is called a motherboard.
The motherboard, also called a mainboard or mobo, lets the CPU (central processing unit) grab data from permanent storage, such as a hard disk drive or CD-RW (CD rewriteable) drive, or from temporary storage, such as RAM. When you click your mouse to tell your computer to save your report to the hard drive, it carries your command to the CPU and displays the results on your monitor. The motherboard is really the foundation of your computer, as it can determine how fast the processor can run, how much RAM the system can have, and the types of peripherals (additional devices, such as printers) and expansion cards (also called daughter-cards, such as 3D graphics cards) the PC can use.
 Types Of Motherboards.
Motherboards come in different form factors (configurations and sizes) to fit in computers large and small, but virtually all boards manufactured today are of the ATX (Advanced Technology Extended) type. Motherboards made in the 1990s were typically variations on the AT (Advanced Technology) style, which required a computer to have a different power supply (a transformer that provides 12-volt and 5-volt power to the motherboard and drives) than newer ATX systems.
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Until a few years ago, users had to move jumpers (plastic blocks with wires inside) on electrical pins to change many motherboard settings. Today, you can adjust most settings in the BIOS (Basic Input/Output System) Setup screen accessible when you start the
computer. | Among ATX's improvements over AT is a replaceable plate for the rear panel of the computer. Because motherboard manufacturers can include a tailored metal plate with each board, they can mount ports (connectors such as USB [Universal Serial Bus]) and audio jacks on the rear of the board any way they like. ATX boards and power supplies also have power cable connectors that can't connect the wrong way. It was easy to confuse AT's two power connectors and incorrectly hook them up to the system's motherboard.
Currently, ATX motherboards support processors that have the same patterns of pins (electrical connections) as either Intel (http://www.intel.com) or AMD (http://www.amd.com) chips. See the "CPU Sockets & Slots" sidebar in this article for more on the common styles of processor sockets.
Within these two design camps are form factors such as Mini ATX (as big as 11.2 inches x 8.2 inches), FlexATX (as big as 9 inches x 7.5 inches), microATX (as big as 9.6 inches x 9.6 inches), and ATX itself (12 inches x 9.6 inches). Smaller motherboards make it possible to build miniature PCs and related devices, such as PVRs (personal video recorders). Recently, motherboard manufacturer Shuttle (http://us.shuttle.com) has been selling boards and computer cases no bigger than a breadbox, such as the 10.6- x 7.5- x 6.7-inch SV25 ($195).
Chipsets & RAM. Besides the microprocessor, there are two main chips, called a chipset, on most motherboards. The one closest on the motherboard to the CPU is traditionally called the northbridge, but can go by other names, such as MCH (Memory Controller Hub) in Intel's 865 chipset or the IGP (Integrated Graphics Processor) or SPP (System Platform Processor) in NVIDIA's nForce2. This chip is a liaison between the CPU and the RAM, the graphics bus (video data pathway), and the system's southbridge.
The southbridge is also called the ICH (Input/Output Controller Hub) in some Intel chipsets or MCP (Media and Communications Processor) in the nForce chipsets. It controls data flow between the northbridge and the hard drive, PCI (Peripheral Component Interconnect) bus, and other ports, such as USB (Universal Serial Bus). Some southbridges support FireWire (50MBps), 802.11 Wi-Fi wireless networking (less than 1MBps), onboard audio, and other technologies.
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Most ATX boards come with a custom-made rear panel to fit their ports. The thin metal panel presses into the back of the computer case. | Most motherboards have other chips that add specific features, such as Silicon Image's PB3112A chip for Serial ATA (AT Attachment) hard drive support. A few chipsets, such as the SiS 735, cut cost and boost performance by packing northbridge and southbridge functions into a single chip.
RAM. RAM acts as temporary storage for data the CPU needs. Also called memory, it's faster than a hard drive (which unlike RAM can retain data even when the computer is off), yet is slower than the CPU's own memory, called cache.
One fast but slow-selling type of RAM is RDRAM (Rambus dynamic RAM; 600MHz [megahertz] to 1,200MHz [1.2GHz (gigahertz)]; 184 or 232 pins in desktop PCs), only found in Pentium 4 systems. SDRAM (synchronous DRAM; 66MHz to 133MHz; 168 pins) is slower than RDRAM but is less expensive and compatible with more chipsets. Its faster variation DDR SDRAM (double-data-rate synchronous DRAM; 133MHz to 200MHz or more; 184 pins) is now common on mainstream P4 and Athlon XP motherboards.
SDRAM modules are called DIMMs (dual in-line memory modules) because they have pins on both sides of the module. RDRAM modules are called RIMMs, although that's not an acronym for Rambus IMMs. Older types of memory, such as FPM (fast page mode) and EDO (extended data output) DRAM, came in modules called SIMMs (single IMMs) with 30 or 72 pins on one side only.
Buses, Slots & Ports.
All the chips on a motherboard would have nothing to do if they couldn't talk to each other. Buses are groups of wires that connect the chips together and let them communicate. Buses have different bandwidths, or data carrying capacities, depending on the devices they need to connect.
The system bus or FSB (frontside bus) connects the CPU, northbridge, and RAM. It might operate as fast as 200MHz on newer motherboards. Pentium 4s can send or receive four bits of data per clock cycle (1Hz), so Intel claims that recent P4s have 800MHz (4 x 200MHz) or 533MHz (4 x 133MHz) FSBs. AMD's Athlon XP processors transceive two bits per cycle, as seen in 266MHz FSB chips running on motherboards with 133MHz system buses. At this writing, 333MHz FSB (2 x 166MHz) Athlons are available and 400MHz FSB (2 x 200MHz) chips are expected soon.
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Old AT boards required two similar power connectors (top), which were easy to mix up. ATX boards use a power connector that only hooks up one way, plus a small secondary lead in some cases. | Of course, the RAM must be able to keep up with a processor and motherboard's FSB speed, or it will slow down the PC. Manufacturers rate RAM modules by their speed capabilities, but manufacturers don't always use the same rating system. For example, PC1066 RDRAM (2.1GBps) is named for its top supported FSB speed, 1,066MHz. Meanwhile, DDR SDRAM and sometimes RDRAM are named for their theoretical data transfer speeds. For instance, PC3200 DDR supports 200MHz FSB speeds, yielding 3,200MBps (3.2GBps) potential data transfer speeds.
Some new motherboards, such as those based on Intel's 865 or NVIDIA's nForce chipsets, support dual-channel memory. Dual-channel simply means that the CPU can address pairs of RAM modules to get twice the amount of data in the same amount of time. Early motherboards for the first Pentium processor used the same technique, as SIMMs of the day couldn't keep up with the CPU's demands.
Slots. Expansion slots and ports pick up where a chipset's capabilities end, as they let you connect supplemental devices and drives to your motherboard. For example, if you want to add a fast, new external hard drive to your PC but lack a port to connect it to, you can install a FireWire or Hi-Speed USB 2.0 adapter card in one of your motherboard's white PCI slots. Some space-saving motherboard designs use daughtercards that provide expansion slots facing sideways, so any added cards lie parallel to the motherboard.
The 33MHz, 32-bit (the amount of data the bus can carry per clock cycle) PCI bus found on most motherboards carries as much as 133MBps. In certain cases, a motherboard may have a 64-bit, 33MHz PCI slot that can carry as much as 266MBps; a 64-bit, 66MHz, 533MBps slot; or even a 64-bit, 133MHz, 1,066-MBps PCI-X slot. Most boards have two to five PCI slots.
The AGP (Accelerated Graphics Port) bus is generally faster than PCI and operates at 66MHz to 533MHz. It's strictly used for graphics cards, such as the 3D accelerator cards that allow more realistic video games and CAD (computer-aided design). Theoretical speeds for brown AGP slots have increased over the last few years from 1X (266MBps) to 2X (533MBps), 4X (1.1GBps), and recently 8X (2.1GBps). AGP Pro slots are slightly longer and incorporate additional power lines for high-end, professional graphics cards. At this writing, the faster PCI Express bus (125MBps per signal line) is expected to begin replacing or complementing AGP and PCI in motherboards late next year.
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AGP (Accelerated Graphics Port) cards for graphics (top) fit in a single brown expansion slot on the motherboard. Multipurpose PCI (Peripheral Component Interconnect) cards (bottom) seat into white slots, of which there are usually two to five on a mobo. | Older motherboards have ISA (Indus-try Standard Architecture) slots, which are longer than PCI or AGP and typically black. ISA's slow pace and tricky card setup soon gave way to PCI's easy plug and play operation. Some less useful, shorter slots still found today are AMR (Audio/Modem Riser) and CNR (Communication and Networking Riser). These never really caught on, but some mainboard manufacturers still include them.
Drive buses. The EIDE (Enhanced Integrated Drive Electronics) bus supports common hard drives, plus CD-ROM, CD-RW, and rewriteable DVD drives through a standard known as ATAPI (ATA Packet Interface). Most mainboards have two 39-pin EIDE headers (connectors), each of which looks like two rows of pins that connect to the drives' ribbon-like data cables. The 7-pin Serial ATA interface, which uses thinner cables and has a higher top speed (150MBps initially), should gradually re-place EIDE.
Some motherboards have four EIDE headers, two of which are for hard drives in a RAID (redundant array of independent disks) configuration. Put simply, a RAID can split data onto two (or more) drives for greater speed, copy identical data to both drives for backup purposes, or both.
The floppy drive has a header that looks similar to EIDE's, but has a smaller, 34-pin connector and a data cable with a twist in some of its wires. Both EIDE and floppy cables can support as many as two drives.
Ports. Depending on the chipset's features, a motherboard might have built-in ports for video, audio, an Ethernet LAN (local-area network), USB 2.0 or 1.1, FireWire, Bluetooth (a short-range wireless networking standard), or other computertechnologies. Although adapters and graphics cards may offer faster performance in some cases, it's usually cheapest to buy these features integrated into the motherboard. 
by Marty Sems
CPU Sockets & Slots
After Socket 7, the last CPU socket Intel created to support the first Pentium processors, the chip manufacturer decided not to let competitors AMD, Cyrix, and IDT make CPUs that were compatible with its new Slot 1 for Pentium II motherboards. AMD made its own Slot A for the Athlon processor, but both Intel and AMD soon returned to making socketed chips. Today, VIA makes C3 processors that fit Intel's Socket 370, while Transmeta's Crusoe BGA (Ball Grid Array) chips use metal bumps instead of pins to fit a 474-ball socket.
| Item | What To Look For | | CPU (Central Processing Unit) Speed | With Intel's CPUs (such as the current Pentium 4) faster is better; when examining a system with an Advanced Micro Devices (AMD) CPU look for the highest number (such as the Athlon XP 3000+) rather than the CPU speed. | | RAM (Random-Access Memory) | More RAM is always better, although some types are more efficient than others; DDR SDRAM (double-data rate synchronous dynamic RAM) is a long name for a currently popular type of RAM. | | Video Card | If you want better-than-average graphics performance (that is, if you'll be working with digital photos and video, large graphics, or high-power 3D computer games), look for a separate video card with at least 64MB of video RAM. | | Upgradability | Although you might be happy with a computer's performance when you first buy it, that might not be the case down the road; make sure it has available expansion slots and that if need be you can increase the amount of RAM sometime down the road. | | Service & Warranty | A one-year warranty on parts and labor is common, but make sure of what you're getting in terms of telephone technical support and on-site service before you buy a computer. | | Price | Price will vary greatly depending on what you want your computer to do; use the examples in the "Computer Shopping Spree" sidebar as a guide. | |
View the graphic "Parts Of A Motherboard" that accompanies this article.
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Put simply, a computer consists of a microprocessor that does the "thinking" (just mathematical calculations, really), data storage devices that hold the information the microprocessor needs, and a monitor, keyboard, and mouse that let you tell the processor what to "think" about next. The large circuit board that connects all of these things together in your PC is called a motherboard. 
