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Your motherboard revealed, part 2

In this Daily Drill Down, Ken Dwight continues his introduction to the components of the motherboard that he began in part one. Learn about crystals, RF chokes, and more.


In my last Daily Drill Down, Your motherboard revealed, part 1, I began an overview of important motherboard components such as processors, the main logic chipset, the system BIOS, expansion slots, memory sockets, the CMOS battery, and connectors. There are several additional components on the motherboard that may be of some interest to you. The exact location and description of these pieces will vary from one motherboard to another, but you will immediately recognize them if they are present on any particular board with which you’re working. In this Daily Drill Down, I’ll explain crystals, RF chokes, and more.

Level 2 cache
The level 2 (L2), or secondary, cache may be found on the motherboard of classic Pentium (socket 7) and earlier boards. Pentium II, Pentium III, and most Celeron processors have a level 2 cache integrated into the actual processor housing, so the motherboard won’t contain L2 cache memory.

Wherever it is located, a level 2 cache significantly improves the performance of any processor. A level 1, or primary, cache is always integrated into the Pentium processor, as it was in the 486 processors. A cache is a very fast, but also relatively small, amount of memory. A level 1 cache on 486-series processors is 8 KB; on classic Pentium processors, it is 16 KB; and on Pentium II, Pentium III, and Celeron processors, it is 32 KB. A level 1 cache operates at the full speed of the processor.

A level 2 cache is typically 256 KB or 512 KB on classic Pentium motherboards; the level 2 cache integrated into Pentium II and Pentium III processors is 512 KB; the Celeron processors with a level 2 cache contain 128 KB. An L2 cache is normally much slower than level 1 but still much faster than the main system RAM. The exception is the most recent Celeron processors, on which the L2 cache runs at full processor speed.

On socket 7 motherboards, the method used to implement a level 2 cache may take any of three general forms: traditional sockets for standard memory chips; a memory socket similar to a SIMM socket, which accepts a module called Cache On A Stick, or COAST; or a permanently mounted memory chip or two, soldered onto the board.

Traditional memory sockets for cache are the oldest form of cache installation, followed by COAST sockets. Most current production motherboards use permanently mounted memory chips, which are not easily recognizable. If you don’t see any obvious provisions for cache on a particular motherboard, look for a jumper or dip switch with possible values of 256 KB or 512 KB. If you find such a setting, you have a pretty good indication of how much L2 cache is installed on the board.

The quartz crystal
Every motherboard will have at least one quartz crystal. This generates the basic timing signal that is used to produce the various frequencies required by the different parts of the system bus, as well as the processor speed itself. The crystal will usually be in the form of a small silver-colored can, about 1/8-inch high, mounted on the board with its top end visible. That end of the crystal will usually have a frequency printed on it, typically 14.318 MHz (see Figure A).

Figure A
Quartz crystals generate the basic timing signals needed by the system bus and CPU. (Photo by Jim Barnes)


The crystal will sometimes be full-height, about 1/2-inch mounted end up or occasionally mounted horizontally on the motherboard. There may be more than one crystal on a motherboard, depending upon the functionality integrated into the board. Some input/output devices, such as video adapters and network interface cards, require their own crystals. If these features are built into the motherboard, the board will have additional crystals to provide the necessary timing signals.

None of these crystals is replaceable or user serviceable, but the question sometimes arises as to their name and purpose. Now you have an explanation for anyone who asks.

RF chokes
On some motherboards you will see unusual but pretty components that look like small Lifesavers candies with copper wire wrapped around them. These are radio frequency chokes, or RF chokes, and they’re used to reduce interference with other electronic devices such as television sets.

Every motherboard design does not require RF chokes, so you may or may not see any on the motherboard you’re working with. If your board has any, they will be part of the power supply circuitry.

Like the quartz crystal, RF chokes are not components that you will be removing or replacing, but users are frequently curious about what they’re called and what they do. Now you can answer their questions about these cute little donut-looking thingies (see Figure B).

Figure B
RF chokes are necessary to reduce radio frequency interference encountered from other electronic devices. (Photo by Jim Barnes)


Heat sinks
You will definitely find at least one heat sink on your motherboard—possibly several. A heat sink is just a set of metal “fins” attached to a component that generates a relatively large amount of heat. Such a piece in every system is the main processor itself, which will be an Intel Pentium or equivalent in most of the systems for which you’re responsible.

A heat sink serves the same purpose as a radiator in an automobile—to pull the heat out of the component and let the primary cooling fan in the system remove the heat. The heat sink on your processor may also have a secondary fan attached directly to it to improve the processor cooling even further.

The most reliable form of heat sink on the processor is one with a sufficient number and size of fins that it doesn’t require a supplemental fan. There are a number of processor heat sink configurations, but the larger it is and the more fins it has, the less need there is for a separate fan.

The main disadvantage to a processor fan is the possibility that it will fail. If this happens, you probably won’t notice any difference in the sound produced by the system. Most of the noise you hear from a computer is the main cooling fan in the power supply, which is much louder than a processor fan. If the processor fan quits working, you may not know the difference until it’s too late.

To prevent possible damage to the processor in the event of processor fan failure, check your BIOS settings to see if there’s an option for a processor fan alarm. If so, be sure that the fan is properly connected to the motherboard and that this option is enabled. In addition, most modern motherboards have the ability to monitor actual temperatures inside the case and set off an alarm if the temperature rises above an acceptable level. If your motherboard and case support such an alarm, be sure it’s enabled as well.

In addition to the heat sink on your processor, other components on the motherboard may also have their own heat sinks. These are most commonly found on power transistors and integrated circuits in the power supply circuitry of the board. They may range from a few fins attached to a single component to huge L-shaped heat sinks on a corner of the motherboard that serve multiple components (see Figure C).

Figure C
Many components besides the CPU require heat sinks. (Photo by Jim Barnes)


Conclusion
This concludes my summary of the various components and functions of most motherboards. In these two Daily Drill Downs, we discussed the most significant features of motherboards you’re likely to encounter, and we explored some of the variables that come into play with boards of different ages and capabilities.
Many TechProGuild Daily Drill Downs and Daily Features describe motherboard features in detail. Here are a few you might be interested in reading:The authors and editors have taken care in preparation of the content contained herein but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.

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