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Refresh your ATX motherboard knowledge

What do you know about modern motherboards? A lot has changed in the last few years with Pentium 4 and AMD processors. Here's a refresher course on common ATX motherboard features, CPU configurations, and identifying them without opening your PC's case.


Motherboards are the PC's backbone, but how much do you really know about them? Sure, you probably know the difference between an ISA and PCI slot, but what about the different types of processor interfaces, chipsets, and memory configurations? In this first article of a three-part series, we will look at common ATX motherboard traits, processor interfaces, and ways to identify an ATX motherboard without opening a computer's case.

A note about avoiding motherboard damage
When you’re zapped by a discharge of static electricity, you’re receiving a jolt of about 1,000 volts. Now consider this: It only takes 20 volts to damage a motherboard. Electrical surges can ping-pong through the motherboard, leaving little damaged areas. Nothing may happen immediately following a surge, but after a while, the system may unexpectedly halt or may not respond correctly. Always take precautions to keep motherboards free of electrical zaps, dust, water, and other damaging elements.

Common ATX motherboard traits
Compared to older motherboards, the newer boards are less cluttered, with the expansion slots at one end, the CPU and memory at the other end, and all the ports mounted along the edge in a two-tiered cluster. The ATX motherboard exhibits such tidy design. No more jumbled cable nests plugged in amongst the expansion slots and running to slot covers or knockouts stamped in the PC case. Figure A shows a typical ATX motherboard.

Figure A
A note to technically minded readers: As motherboard chipsets have developed, a few very-large-scale integration (VLSI) circuit chips are beginning to incorporate some functions formerly performed by discrete chips.


CPU configurations
This article will focus on the most common CPU interfaces, but others are available, and new ones are constantly being developed. ATX boards can be configured for a variety of CPU interfaces, including Socket 5, Socket 7 (for AMD K6-2 CPUs), Slot 1 (for Pentium II and III CPUs), Socket 370 (for Via CPUs), Socket 423 (for Intel Pentium 4s), and Socket A (for AMD Athlon and Duron processors).

Figure B


As Figure B shows, Socket 7 and Socket 5 are quite similar, but there are differences. Socket 7 requires 5.0 amps at 3.3 volts, and Socket 5 requires only 4.33 amps. Socket 7 also comes with the 321st pin designated as a key pin, with no electrical connection to either the CPU or motherboard. Socket 7 can handle all the predecessors of Socket 5. Maximum speed for a Socket 5 processor is 133 MHz, although some go only as fast as 120 MHz.

Intel moved to the Socket 370, Slot 1, and Slot 2 processors with the release of its Pentium II, Celeron, and Xeon processors. Figure C shows a Socket 370 motherboard, and Figure D shows a Slot 1.

Figure C


Figure D


Celeron processors usually use a Socket 370 motherboard, but depending on the CPU configuration, they can also use Slot 1 motherboards. Figure E shows an example of an adapter card that allows Slot 1 motherboards to use a Socket 370 CPU. Pentium II and Pentium III processors use Slot 1 motherboards, while the Slot 2 interface is reserved for Intel's high-end Xeon chip.

Figure E


More recently, Intel has introduced the Pentium 4 processor shown in Figure F. The Pentium 4 is based on Intel's new Netburst microarchitecture, instead of the older P6 core, yet is still x86 compatible. The current version of the Pentium 4 uses a 423-pin motherboard interface (Socket 423). It is likely that future Pentium 4 releases will use a new mPGA478 interface, with 55 more pins than the Socket 423.

Figure F


Intel, however, is not the only game in town. The Athlon and Duron chips from Advanced Micro Devices (AMD) are very popular on desktop PCs. The Athlon and lower-cost Duron, shown in Figure G, use a Socket A motherboard interface.

Figure G


ZIF vs. LIF
CPUs can also be categorized by insertion type. A zero-insertion-force, or ZIF, CPU is a drop-in unit. Once you drop it into the proper holes, you can close the small handle and lock it in. LIF stands for low insertion force; this one is pressed in gently with no handle to lock it in. Always take care to line up the CPU pins accurately before trying to push it in or close the handle, as these pins are easy to bend.

For a great way to obtain information about your CPU, try CPU-Z, a freeware program that provides information about stepping, type of slot, manufacturer, and so forth.

How to ID an ATX motherboard without opening the case
The best way to identify an ATX motherboard without opening the case is to look at the back of the PC, as shown in Figure H. All of the expansion cards plug perpendicularly into the motherboard, not into a riser card as with the LPX or NLX motherboards. The other clue is that the I/O ports are in a double row at the end opposite the expansion slots.

Figure H


More to come
In the next two articles in this series, we’ll cover the following information:
  • What power supplies to use with various motherboards
  • The types of memory you can use and how to identify them
  • How to tell if you have sound/video/network on board
  • How to tell IDE from SCSI
  • How to find the vendor and model number on a motherboard

We’ll also go over a lot of those difficult-to-identify elements of the motherboard, such as I/O controllers, graphics controllers, slots for expansion cards, and so on.

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