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The Power Supply Unit (PSU) used in desktop PCs/computers, making a good choice of motherboard, etc. - Page 3


Page 1 - The motherboard (mainboard) and PC case used in desktop computers

Page 2 - Desktop PC ATX cases and case fans

This page - The Power Supply Unit (PSU) used in desktop computers, making a good choice of motherboard, etc.

Page 4 - Sundry useful motherboard information


Click here! to visit the page on this site devoted to motherboard and power supply problems and their solutions.


Click here! to go to information on this site on what you need to consider when upgrading a PC's motherboard.

Enermax (top) and Antec PSUs

The image above shows two PC power supply units.


NOTE WELL - BEFORE TURNING A POWER SUPPLY ON, ENSURE THAT THE VOLTAGE SELECTION SWITCH ON THE PSU IS SET CORRECTLY (230V in the UK -110V in the USA). Most power supplies switch to the correct voltage automatically, but you should make sure that any switch is set to the correct voltage used by your country's mains electricity supply. The following webpage covers the mains electricity voltages used in various countries.

Mains electricity -

PSU Repair: A Case Study [June 2015] -

Remember that PSUs contain capacitors that retain their charge long after being disconnected from the mains supply, so never work on PSUs unless you know what you're doing. There are plenty of videos on YouTube and articles on the web on repairing PSUs, some better or much better than others.,review-33227.html

Failure to ensure this switch is set to the correct voltage can destroy your power supply unit or at the very least blow a fuse in it. - And do not use the power supply unit unless it has a load attached to the motherboard, such as the video card and hard disk drive. Turning the power on with only the motherboard attached to it, could also destroy the power supply unit, which must have a load to function without burning out.

Click here! to see an annotated image of an ATX power supply unit on this website.

The job of the power supply unit (PSU), usually just called the power supply, is to deliver a stable voltage to the PC's components via its motherboard. If it does not do that, the PC will crash (stop working) and the components can be fatally damaged. If it fails to work, none of the PC components can be powered up.

The power supplies used in standard desktop PCs comply with the ATX standard, ATX12V 2.0, and the maximum power output is measured in Watts. The average computer should have a 500W unit, with a 650W to 750W unit for a power-hungry PC that uses one or more high-end graphics cards or many hard disk and CD/DVD drives. Note that a power supply with a maximum output of 650W won't be drawing that much power all the time like a 100W light bulb does; it will only output as much power as the computer requires.

The following power cables/connectors are supplied by most ATX12V 2.0 power supplies:

1. - Molex. Used to provide power to older IDE hard disk and CD/DVD drives and internal case fans. An adapter can be purchased to convert it into a 6-pin PCI Express (PCI-E) connector required for the auxiliary power required by some graphics cards. A Molex connector cannot be converted into an 8-pin PCI-E connector used by some graphics cards.

2. - PCI-E. Used to provide auxiliary power to graphics cards that use the PCI Express standard and can have 6 or 8 pins. As mentioned above, there is no adapter cable available to convert a standard Molex connector to the 8-pin type. Most 8-pin connectors have a detachable 2-pin section that converts it into a 6-pin connector.

3. - 24-pin ATX power connector. This is the main connector that connects the power supply to the motherboard. Some of them (not all) have a 20-pin section and a detachable 4-pin section. When the 4-pin section is detached the power connector can be connected to the older 20-pin connection point provided on older motherboards for the older ATX 1.3 power supplies.

4. - SATA. Used to provide power to the latest hard disk and CD/DVD/Blu-ray optical disc drives and SSD data-storage drives that can be used instead of standard hard disk drives.

5. - Secondary ATX connector. Motherboards have required to be powered a secondary power connector since about 2005. It was a 4-pin connector for a long time, but new motherboards now require an 8-pin connector. Most 8-pin auxiliary power connectors can be split into two 4-pin connectors so that they can be used with an older motherboard that supports the ATX 1.3 power standard.

If you visit the following webpage and click on the motherboard, you will be able to click on the large version that is presented and the area you have clicked on will produce a magnification of that area of the board. The 8-pin auxiliary power connector is in the top right-hand corner and the main 24-pin connector is in the middle of the bottom section under the four memory slots.

GA-Z68XP-UD3P Socket LGA1155 motherboard for Intel's second-generation Core i3, i5, i7 processors -

Note that a modular power supply allows the user to add the power cables as required instead of having all of the available connectors, which are not removable, coming from the power supply.

The power supply is connected to the mains electricity supply via a power cable and the power supply is connected to the PC's motherboard via the power supply's power connectors. Most motherboards must be connected to a main power connector and an auxiliary power connector from the power supply. If the auxiliary power connector is not connected, the PC will not boot. The computer's components are powered only via the motherboard (most adapter cards, such as network cards and sound cards) or only by the power supply, as is the case with hard disk and optical disc drives. Some high-end graphics cards are powered from the motherboard and require to be connected to up to two power connectors from the power supply; most low-end graphics cards just require to be installed in a slot on the motherboard.

When the PC's Power button is pressed a jumper is shorted and the motherboard switches the power supply on, which then provides power to the PC's components. Therefore, if the power supply is not connected to the motherboard and its fan works when its own power switch is on and the mains supply is turned on, the power supply is faulty. If the power supply doesn't work when the Power button is pressed, the motherboard is not turning the power supply on. The motherboard itself is therefore probably faulty or its connections to the power supply are not properly connected.

What happens when the Power button is pressed when the computer is working is set under Power Options in the Windows Control Panel. The available settings can make the computer go into hibernation, go into standby mode or switch off.

The power supply unit is one of the most overlooked components in a PC. I suppose the reason is that most people simply believe that if a power supply unit has the physical capacity to be connected to as many other components via the motherboard then it must be able to deliver the quality of power that they require. Unfortunately, that is often not the case, because the power supply in a desktop computer, or the power supply that comes with a PC case, can be underpowered or of low quality. If that is the case and you install a high-end graphics card or a dual-core or quad-core processor, the system could become unstable or might even fail to boot.

Note that most power supplies are the same size and should fit into a standard ATX case, but some of them, such as the Zalman ZM500-HP, Hiper Type M 670W, and Tagan Dual-Engine 700W, have more depth than is usual, so make sure that you can fit a power supply in your PC case before you buy it by checking its dimensions.

In the UK, a power supply uses the 230V AC mains supply and tranforms it into power at the correct voltages for the computer's components.

The following webpage provides images of the connectors that a modern power supply unit provides.

All about the various PC power supply cables and connectors -

Read the following webpage called How to Spot an Efficient PSU (Sept. 2011). The more efficient a power supply is the better its quality. The rest of the article is on how power supplies work, which you might find of interest. -,review-32270-5.html

Choosing a power supply for a self-built desktop PC or a PC that you intend to buy and then upgrade

In 2005, I bought an Advent desktop PC from PC World for office use that came with a decent power supply unit. When it gave up the ghost, I looked at the specs and bought another Advent desktop PC from PC World, but when I opened the case it had a very light 300W switching power supply made by ISO that can be purchased for $15, so I replaced it with a decent 400W model made by Corsair, because if the power supply goes it can take the other components with it. The power supply wasn't listed in the specs. This is the one component that PC manufacturers can skimp on without the buyer noticing it, so you have to check what is installed yourself. Even reputable case manufactures, such as Foxconn, are using these cheap ISO power supplies in their cases.

Here is a video review of an "Alpine Black 700W Silent Quiet PC ATX PSU" priced at £17.65, which an self-builder should avoid like the plague:

Here is his printed review: "In the video I voiced my concern of how light the PSU was. My concern was justified with the initial power-up on a newly built PC. It does not provide 700W [he ordered a 650W model but was delivered a 700W unit] and the power (Amps) associated with that, or anything close to that over a sustained period. I used it for the initial turn on and install of Windows 7. The system was very unstable - flashing screen, slow processor speed etc.. Being a new build the cause could have been any number of components. But when I replaced it with a more upmarket model which had a lower wattage specification, everything worked properly. The total power requirement of the system I built is only 460W on full load, which should have been no problem for this 700W PSU. Since some purchasers have had no problem with it but others have, it is obviously only suitable for an older computer or one with a low specification. It is still quite possible to build a reasonably powerful PC today that uses no more than 300W if you use an integrated motherboard that provides video and sound. For instance, one using an AMD A-Series APU processor, which all have an onboard AMD graphics chip, and a motherboard with integrated sound."

Choosing a power supply for your self-built desktop PC is an important factor that can easily be underdone or overdone, depending on your computing needs. A gaming computer requires much more power than an office computer. The following power calculator allows you to enter the components. When all of the components are entered, the calculator tells you the wattage you require, which allows you to choose a power supply that provides that wattage plus some overhead just in case all of the components are being used at the same time.

Enermax Power Supply Calculator -

And here is the eXtreme Power Supply Calculator Lite -

Performance Charts Power Supplies (230V UK and 120V US] -

"Our new power supply charts include a growing number of desktop power supply devices. Our testing focuses both on cost efficient entry-level units with only a few hundred Watts as well as high-end devices up to 80 PLUS Gold units, which deliver great power efficiency and features." -,26.html

Beware of poor-quality dangerous desktop PC power supply units

Andrew Foster bought a Palicomp Core i3 Blast 530OC-22Plus desktop PC. Read the following review of it to see that no mention was made of the power supply unit, which, unfortunately, is the case with most desktop PC reviews. The power supplies used in laptop PCs are not usually a problem because, being an external unit that connects to the laptop, they have to be made to a high specification.

Palicomp Core i3 Blast 530OC-22Plus review -

This is what he said happened with the power supply unit of his PC: "It [the PC] worked well for two days and then the power supply blew up - quite spectacularly, with banging and fizzing. Rather than going through the hassle of sending the entire computer back, I replaced the power supply myself and the computer has worked perfectly since. I dismantled the original power supply (not normally recommended but I'm a Chartered Electrical Engineer) and was horrified by the poor quality of the assembly. The leads connecting to the power supply inlet weren't shrouded, and the capacitors on the input filter were under-rated. Components were soldered to the board so shoddily in places that some of the leads were in danger of touching. In fact, I believe this was the cause of failure. I did an internet search for this model of power supply ("ATX-650" manufactured by "Eye-T") and found it available for just L12.50. You wouldn't usually expect to pay less than L40 for a good-quality 650W power supply. I've carried out a thorough inspection of the rest of the computer, and everything else is in good order. The other components are of a good quality and the workmanship is fine. A month later I haven't had a single glitch. It makes me wonder why a computer manufacturer would go to the trouble of building a good-quality computer and then ruin it with such an awful power supply. It concerns me that there may be an attitude in the computer industry that processors, graphics cards and motherboards are worth spending money on but power supplies just sit there and hum so you should buy the cheapest one you can. The power supply is arguably the most critical part of the computer - if it goes wrong it can damage any or all of the other parts, and in the worst case it could even burn down your house (as mine almost did). Manufacturers need to pay attention to the quality of their power supplies to avoid expensive warranty returns, or worse."

Some power supplies have a switch to change between 230V (used in the UK) and 115V (used in the USA), but other models have automatic sensors that switch input voltage automatically, or are able to accept any voltage between those limits. If the power supply uses a switch, you must make sure, having just installed it, that you have it set to use the correct voltage before you switch the computer on. The following Q&A discusses what can happen if you have the 115V switch selected in the UK., which uses 230V mains. In that case, only the fuse in the power supply, which can be replaced easily, probably blew.

PSU Popped, what now? -

Different components require different voltages, so a power supply is really several power supplies in one unit. Each supply is called a rail. All power supplies have three main rails - 3.3V, 5V, and 12V - two secondary standby rails - 12V and 5V. A power supply's maximum wattage (e.g., 700W) is the total power it can supply across all of its rails. Some power supplies can have up to four 12V rails. These are used to power PCs running powerful components so that they can each have their own rail. The 12V rail (or rails) is/are of particular importance because it/they powers/power the PC's processor and graphics card.

However, test of quality power supplies that use both a single 12v rail and more than one are found to be stable at all loads.

Power supply rail -

How to distinguish between power supply units of low and high quality

"It's easy to tell if a PC power supply is working or not. However, until now it has been hard for a PC end-user to measure the quality and reliability of a power supply. Herein we attempt to document a very simple way to estimate the quality of a computer power supply by the weight. We measured the weights of 38 standard ATX power supplies of different wattages, models and manufacturers. The weight data were then correlated with the current price and wattage on the label. The findings are in agreement with the return rates and general experience we accumulated from many years of selling and servicing power supplies." -

Who's Who In Power Supplies: Brands, Labels, And OEMs [November 2010] -

"Did you think all power supplies were manufactured by the brand selling them? We show you what makes a good PSU and reveal who actually builds PSUs. You can actually find lots of quality, instead of just scrap metal, behind some of the budget labels." -,review-32046.html

TOM'S HARDWARE GUIDE: Articles on power supplies

Three 1000 W 80 PLUS Gold-Certified Power Supplies Tested [February 2011] -

"We received a trio of 1000 W power supplies priced between $200 and $300, so we ran them through our usual suite of tests to see if they really live up to their 80 PLUS Gold certifications. Surprisingly, all three hiccuped during efficiency testing." -,review-32115.html

Roundup: 12 Gaming Power Supplies Compared [December 2010] -

"Gamers demand a lot from their computers, starting with the PSU. Therefore, almost every PSU manufacturer sells products optimized for gaming PCs. We introduce ripple and noise testing in this roundup to further improve our power supply evaluations." -,review-32088.html

Sub-$75 Mainstream Power Supply Roundup [October 2010] -

"In our last PSU article, we reviewed a bunch of relatively expensive high-performance devices suitable for powerful gaming computers and workstations. The average user typically prefers something a little bit more affordable, though, which is why today we're reviewing a handful of PSUs that can be found for around $75." -,review-32016.html

Bang For Your Buck: Four 500W Power Supplies Reviewed [July 2010] -

"Enthusiasts often say that you can never have too much performance. However, a 500W power supply is perfectly ample for a majority of mid-range PCs. This is one of those cases where a solid ratio of performance to price is preferable to gross excess." -,review-31942.html

Silent PSUs: Fortron Versus Silverstone : Passive Power Supplies In The Lab -,review-31270.html

PSUs: More Important than You Think -,review-2385.html

Each make/model of power supply has its own rating for the amount of power in watts (W) that each rail can deliver. However, the total power rating of a power supply cannot be determined by adding up the rating for each rail, because each rail will not have to be delivering full power all the time. The rating for each rail is just the maximum power that it can deliver if power is available from the total that the unit can generate.

A PC that has a dual-core processor and a mid-range graphics card, such as an nVidia GeForce 8800 GT draws about 250W, so you won't be able to use a 250W power supply because the 12V rail won't be able to deliver the full 250W. A 250W unit is designed to provide power to all of the PC's components, not just the processor and the graphics card. Therefore, it is a good idea to have a power supply that has a total power rating that exceeds the PC's power demands. The same PC with a quad-core processor would require about 320W, so it would be advisable to use a 450 - 500W power supply. A dual-core system can still make do with a quality 400W power supply. Here is a quality 430W power supply for £39.00 (Feb. 2011):

Visit the Home page of and look under Components => Power Supplies and click on the Price heading to go from the lowest to the highest prices if you want an inexpensive PSU. Read the purchaser reviews, if available, which are usually very useful.

The latest high-end graphics cards can draw up to 300W on their own, which means that you would need a power supply rated as 600 to 650W. However, if you have two graphics cards installed using SLI or CrossFire technology, which the motherboard must support, you may require a 700 to 800W power supply.

You can also now install four graphics cards, which will demand even more power.

"Arm yourself with up to four ATI Radeon HD graphics cards to move faster, aim quicker, and see more clearly than all who stand between you and victory. With an ATI CrossFireX gaming rig, you can breakthrough traditional graphics limitations to achieve higher performance and The Ultimate Visual Experience."

The current ATX12V 2.0 standard for power supply units has replaced the previous ATX 1.3 standard.

The old ATX 1.3 standard has a 20-pin power connector that connects the power suppply to the motherboard. The new ATX12V 2.0 standard uses a 24-pin power connector.

An adapter is required to be able to use the new 24-pin plug of a ATX12V 2.0 power supply in motherboards that have theolder ATX 1.3 20-pin connector. Most power supply manufacturers include one with their new ATX12V 2.0 power supplies, because 20-pin connectors are still being used on many motherboards. A 20-pin power-supply cable also fits into the adapter, making it possible to use an old-style power supply unit with a motherboard that has the new 24-pin connector.

An ATX12V 2.0 power supply has several four-pin Molex and SATA connectors/plugs. Molex plugs are connected to IDE ATA CD/DVD optical drives and IDE ATA hard disk drives, and some AGP graphics cards. SATA connectors/plugs connect to SATA hard disk drives and optical SATA CD/DVD drives. Molex-to-SATA adapters that make an Molex plug into an SATA plug are readily available, but SATA-to-Molex adapters are not. You should make sure that any power supply that you buy has enough Molex and SATA cables to connect to the drives that your PC has.

Note that adapter cables are available that bridge the previous and current power supply standards. The following webpage shows which adapters are available:

Power Cable Adapters -

Powerful high-end PCI Express graphics cards connect to a six-pin power connector from the power supply, so if you buy such a card your PC's power supply must have one. The most powerful PCI Express graphics cards require two such connectors, which are also required for dual-card setups.

Note that the very latest ATI graphics cards use a six-pin and an eight-pin PCI Express connector. The Enermax Infiniti 650W power supply provides the correct eight-pin plug.

A dual-core processor can draw up to 130W on its own, and Nvidia and AMD (which bought ATI and incorporated it under the AMD banner) recommend the output of the power supply that can run two or four of their high-end graphics cards in SLI mode and CrossFire/CrossFireX mode respectively.

If you plan on using two or four graphics cards that use either Nvidia's SLI technology or ATI's CrossFire/CrossFireX technology, make sure that your PC has a power supply that explicitly states in its specifications that it supports the particular technology that you want to install.

Both Nvidia and AMD have certification programs for power supplies that are guaranteed to work with two or four graphics cards using SLI or CrossFire/CrossFireX.

A full list of power supplies and the graphics cards that they support can be found at at (for nVidia cards) and

Recommended makes of power supply? - The image above shows power supplies made by two major manufacturers Enermax (top) and Antec. Both companies make cases with power supplies, and separate power supplies. Akasa, Cooler Master, Zalman, Seasonic, and Tagan are reputable major manufacturers of power supplies.

There are many smaller, less well known manufacturers of quality power supplies, such as Jeantech, that makes cases and PSUs. The best-known supplier of Jeantech products in the UK is PC World.

Note that the power supply must be able to run the hardware components that it is intended to be used with, so make sure, for instance, if you are building a PC that uses one of the latest Intel dual-core or quad-core processors, that the ATX12V 2.0 power supply has an additional 8-pin power connector that connects to the motherboard if the make/model of motherboard requires it, because not all current ATX12V 2.0 power supplies provide one.

However every ATX12V 2.0 power supply has the additional 4-pin power connector that is required for AMD Athlon 64 single-core and dual-core processors. Keep reading this page for more information on the power requirements of the different types of components.

Examples of a first-class power supplies that provide both of the additional 4-pin and 8-pin power connectors are the Zalman ZM-460-APS 460W unit, the Cooler Master iGreen Power 500W unit, and the Seasonic S12-430 430W unit.

You can make use of a search engine to find local vendors and reviews of any of the products mentioned above.

Power supplies are often recommended or ridiculed on computer forums.

ATX is a power standard as well as a motherboard standard, as is the new BTX (Balanced Technology Extended) standard, which will eventually replace the ATX standard for power supplies and motherboards.

In June 2007, AMD announced its own DTX form factor, which is similar to Intel's BTX form factor. However, like the BTX form factor, it has failed to be adopted.

Watch the following video if you want to see a demonstration of how to install an ATX power supply in a case and connect its cables to the devices to an ATX motherboard and inside the computer.

How to install a Power Supply [the power connectors for the various devices - motherboard, Molex, SATA hard drive, PCI Graphics card, etc., are shown/discussed] -

Expert Reviews - Latest PSU reviews -

Modular power supplies from Enermax and Antec

Modular power supplies allow the user to attach only the power connectors in use instead of having them all connected to the power supply whether they are in use or not. They come with a full range of cables. Molex cables connect to IDE hard and CD/DVD drives, PCI Express (PCI-E) cables connect to PCI Express video/graphics cards, and SATA cables connect to SATA hard drives. The cables connect to the devices and to dedicated ports on the power supply unit itself.

The following 500W modular power supplies are available from Antec and Enermax.

The Antec Neo HE500 is supplied with six Molex, two PCI-E, and four SATA cables that connect to five modular ports on the power supply. If you want to use a mixture of Molex and SATA cables, you have to use more than one cable.

The Enermax Liberty ELT500AWT is more flexible than the Antec Neo HE500. It has six modular ports on the power supply for both Molex and SATA cables. It has two dedicated PCI-E ports. The Molex and SATA connectors are one one cable. The unit comes with a neat bag in which to store the spare cables.

If you want more information on these power supplies, look them up on the Antec or Enermax sites, or enter the make and model as the search query into a search engine.

Note well that if you are upgrading a computer that is only a few years old by installing new processor, motherboard, RAM, video card, etc., you must also upgrade the power supply unit, because the power requirements and the sensitivity to power fluctuations of the hardware have increased significantly, and it is likely that the 230W PSUs used in most systems then are inadequate now - especially if it is not a unit of high quality. Moreover, current hardware technology uses the different power lines of the power supply differently from earlier technology.

The new power supply standard: ATX12V 2.0

A new ATX standard for power supply units is available and is set to replace the previous ATX 1.3 standard. It's called ATX12V 2.0.

The ATX 1.3 standard has a 20-pin power connector that connects the power suppply to the motherboard. The ATX12V 2.0 standard uses a 24-pin power connector.

An adapter is required to be able to use the new 24-pin plug of a ATX12V 2.0 power supply in motherboards that have the current ATX 1.3 20-pin connector. Most power supply manufacturers include one with their new ATX12V 2.0 power supplies, because 20-pin connectors are still being used on most motherboards. A 20-pin power-supply cable also fits into the adapter, making it possible to use an old-style power supply unit with a motherboard that has the new 24-pin connector.

Note that the motherboards for Intel Pentium 4 and AMD Athlon 64 processors have what is called an additional ATX 12V Power Connector. It is a small square box on the motherboard for a four-pin plug from an ATX12V 2.0 power supply unit. Here is what a motherboard manual from MSI says about the connector: "MSI Reminds You... 1. These two connectors connect to the ATX power supply and have to work together to ensure stable operation of the mainboard. 2. Power supply of 350 watts (and above) is highly recommended for system stability. 3. ATX 12V power connection should be greater than 18A." Most motherboards with this connector won't boot unless it is connected. The connector is also present on most recent 20-pin ATX 1.3 power supply units. I have such a PSU that is a few years old and it has the connector.

If you want to see images of the two power connectors that connect to motherboards running Intel Pentium 4 and AMD Athlon 64 processors, download the user manual for the Socket 939 MS-7100 (aka K8N Neo4 Platinum/SLI) motherboard made by MSI.

In electrical terminology, A stands for amps, which is a measure of current, V stands for volts, and W stands for watt, the unit that is a measure of power output, which is calculated by multiplying the amperage in amps by the voltage in volts.

The power supply takes the 230V power (115V in the US) from a mains socket and transforms it into power at the voltages that the various components in a PC use. The different components in a PC can require different voltages, which means that a power supply must be several power supplies in one unit. Each separate supply is called a rail or a line. Every power supply has three main rails - the +3.3V, +5V, and +12V rails, plus two secondary -5V and -12V rails as standby rails.

Each rail has a maximum rated current, which is measured in amps (A), that it can provide. Since the amps x volts = watts (A x V = W), and power is measured in watts, each rail's voltage multiplied by its amperage gives the maximum amount of power that it can deliver. However to determine the maximum power output of a particular power supply isn't a matter of adding up the maximum output of all of its rails, because no power supply can supply its rated maximum on every rail at once. Therefore, a rail has a maximum combined wattage (the maximum power that it can deliver when all of the other rails are also working to full capacity), and the sum of all of those maximum outputs gives the power supply unit's maximum output in watts.

The maximum amperage delivered by the +12V rail(s) of a power supply unit (PSU) is of particular importance with modern high-performance systems. The power supply unit itself always has the power details of its different rails printed on it.

Some of the latest power supplies have up to four +12V rails, which can be useful in computers that have very powerful components, because if one component suddenly demands its rail's maximum power output, the other components on the other +12V rails can still draw enough power to keep going. However, note that splitting the amperage across up to four rails also increases the likelihood that one rail might be overloaded while the other rails have power to spare.

Most motherboard manuals tell you what the amperage of the +12V rail/rails have to be in order to power the motherboard properly.

For example, the manual for the MSI RS480M2-IL motherboard, which has an inbuilt video chip and therefore doesn't require a video card to be installed, says that the +12V rail must supply at least 18A (amps) of current. Many cheap off-the-shelf PSUs provide only 15A or less of current on the +12V rail, and therefore can't be used with that motherboard if you want a stable system.

If you want to install a high-end video/graphics card the +12V rail would have to deliver between 20A and 30A. Therefore, you should always make sure that the PSU in a system can match the power requirements of a high-end video card before you buy or install it.

For example, at the time of writing this it is the middle of June, 2005, and nVidia has just released its long-awaited 7800 GTX graphics chip. A single video/graphics card using the chip requires the minimum of a 400W PSU with a +12V rating of 26A, while the SLI, dual-card configuration, requires a 500W PSU with a +12V rating of 34A as the minimum. Most standard PSUs don't usually deliver either 26A or 34A on the +12V rail, so a special PSU is required to run both of those options.

Note well that if you are going to install a power-hungry graphics card (or cards), to make sure that your computer can deliver the required power, you should visit the card manufacturer's site for information on recommended power supplies.

Remember that some power supplies now have as many as four +12V rails/lines in order to split the output. However, note that splitting the amperage across up to four rails also increases the likelihood that one rail might be overloaded while the other rails have power to spare.

High-end PCI Express video/graphics cards have to be connected directly to the PSU.

If a particular power supply doesn't have a PCI Express connector and one is required of it, it's possible to buy an adapter that is fitted to a standard power connector of the kind that fits to standard IDE ATA (non-SATA) disk drives.

The full-sized ATX power supply unit (PSU) that is found in most mid-tower cases uses a form-factor called PS/2. Smaller power supplies are generally found in micro-ATX cases and some OEM mid-tower cases. The most common smaller size is SFX, as found in emachines, Hewlett Packard, and Gateway micro ATX systems. A larger supply called PS3 is most commonly found in Hewlett Packard's mid-tower cases. It has the same width and height as a standard PS/2 power supply but has reduced depth (3.5 inches, compared to 5.5 inches for a PS/2 power supply).

Quality power supplies have thermal and overload reset protection, but units of lower quality make do with only the protection of a fuse, which is more effective at preventing a fire than protecting the system. Moreover, the manufacturers of most of the cheaper power supplies solder the fuse into place in the hope that the unit will be replaced instead of just the fuse should it be blown.

The clusters of wires to the left and right of each unit (shown in the image of two power supplies at the top of this section of the page) have the various Molex plugs (or headers) on their ends that are required to connect drives, the motherboard, heatsink and fan units, and sometimes even adapter cards, such as some FireWire cards, etc., to the power supply.

If you run out of Molex drive headers, you can use a Y power splitter, which adds two headers by plugging it into one header, but, because they can put a greater load on the power cable than it was intended to carry, they should only be used to power devices that don't draw much power.

Newer power supplies all have the ATX 12V header introduced for use with Pentium 4 motherboards. Such power supplies are often labelled as being "Pentium-4 Compatible", even though they work with other ATX platforms, such as Socket A, Socket 754, Socket939 and Socket AM2 motherboards that run AMD's Athlon XP and Athlon 64 processors.

Power headers for Serial-ATA (SATA) hard disk drives have recently become available on some power supplies, so no adapter cable is needed to power them. Some power supplies also even have a tachometer output for connection to a motherboard's fan header. See the image of two SATA adapter cables below. The white plug fits into a power cable connector from the standard ATX power supply and the black plug fits into the SATA hard disk drive:

SATA drive power cables that connect to the PSU (white plug) and the SATA drive (black plug)

The kind of SATA connector shown above does not provide a +3.3V connection, but some new SATA hard disk drives require this voltage. If so, only one of the new ATX12V 2.0 power supply units can provide it. ATX12V 2.0 is the new power supply standard that is going to replace the ATX 1.3 standard. The black 3.3V SATA connector, shown in the image below, is available in straight and angled versions, and comes directly from the ATX12V 2.0 power supply unit so that a conversion cable of the kind shown above is not used. The cable on the right has SATA written on its plug.

SATA hard disk drive power cables that come directly from a new ATX12V 2.0 power supply unit

See the image below of the new ATX12V 2.0 standard, which has a 24-pin plug (right) that connects to the motherboard, whereas the ATX 1.3 standard uses a 20-pin plug (left).

Showing the 24-pin ATX12V 2.0 plug (right) and the old ATX 1.3 20-pin plug

By using adapter cables or special ATX connectors with 20 or 24 pins, the new power-supply specification can be made compatible with the earlier power-supply standard. Therefore, should an old power supply fail, a new replacement using the new standard can be used with the earlier hardware.

Some power supplies can be used with both 20-pin and 24-pin motherboard connectors. The 24-pin plug has a 4-pin plug that can be detached so that it can be fitted to a 20-pin motherboard power connector.

AMD Athlon 64/Phenom and Intel Pentium 4/Core 2 Duo/Core 2 Quad processors require a motherboard with a power supply with an extra 12V connector that is connected to a 4-pin header on the motherboard, as shown in the image on the right. Some motherboards have an 8-pin 12V connector. You should buy a power supply that provides the 8-pin connector to use it with such a motherboard. If you buy a PSU that only provides a cable with a 4-pin connector, you can buy an ATX 4 Pin Male to 8 Pin Female EPS Power Adapter Cable that converts a 4-pin auxiliary power connector into an 8-pin connector from Amazon for about £2.50. A Molex power connector that provides power to non-SATA devices can also be converted to an 8-pin auxiliary power connector by using a 4-pin Molex to 8-pin 12V EPS Motherboard ATX Power Cable Adapter (out of stock on when I looked).

The extra 4-pin 12V power connector from the PSU required to power Intel  and AMD processors

As you can see, the keyed connector can only be connected one way to the motherboard. The hook on the connector fits over the protrusion on the header on the motherboard.

Some power supplies have a connector that splits so that it can have 8 pins or just 4 pins. The animated image below shows such a connector.

An additional 12V power connector that splits into two so that it can be used as a 4-pin or an 8-pin connector

Examples of a first-class power supplies that provide both of the additional 4-pin and 8-pin power connectors are the Zalman ZM-460-APS 460W unit, the Cooler Master iGreen Power 500W unit, and the Seasonic S12-430 430W unit.


It can be very frustrating if a power supply's cables are too short to reach the top or the bottom drive installed in a case, or if the ATX power leads don't reach to the motherboard when, say, it's installed in a full tower case. Lead extenders are available, but it's always best to buy a fully satisfactory power supply in the first place. Most quality brands of power supply provide plenty of cable length, while many of the cheaper brands do not.

Dell owners beware!

"Dell owners beware! Prior to their conversion to standard ATX12v-compliant ATX power supplies for the P4 [Intel Pentium 4 processor], Dell used a variation of the ATX form factor with the power pins in a different orientation! Use of these older, non-standard units on a standard ATX motherboard will at best refuse to work, at worst fry the board. Use of standard ATX power supplies in these older Dell computers will usually fry the power supply, or worse fry both the power supply and motherboard!" - from "A Different Perspective on Power Supplies" that used to be on the forums.

The image below shows the inside of a standard ATX case without any of the components installed. One of the side panel's has been removed. The power supply, with the power cables coming from it, can clearly be seen in the upper left hand corner. The case fan with its cable is just below it. The drive bays are in the upper right hand corner, and below them are the cables that come from the front of the case for the LED lights, the Reset switch, and the Power-on switch, etc. These will be connected to the appropriate block of connection points on the motherboard. For a diagram of the connection block on the motherboard, see this Build Your Own PC page on this site.

Inside an empty case showing the PSU and drive bays

Buy a quality case, because unless you know how to use electronic testing equipment, the only way to find out if a problem has to do with the power supply is to install the same hardware in a different case, or a different set of hardware in the same case.

Note the size of the power supply in the ATX case shown above. It is small, and, as such, will allow unhindered access to the motherboard, which is fitted close to the unopened side. All good quality power supplies are this size nowadays. Do not purchase a case if it has a large, light, square power supply, because it is likely to be cheap, old technology.

It is difficult for non-specialist people to determine the quality of a particular power supply unless they rely on brand names of the manufacturers that are known to produce quality units, such as Antec and Enermax. But the well-known manufacturers are not the only producers of quality power supplies. There are many relatively unknown manufacturers that produce units of quality.

Moreover, a poor-quality power supply doesn't have to be large, it could also be as small as a high-quality unit. So, a good rule of thumb to use is this - better quality power supplies tend to be heavier than those of lower quality. If you take the power supply out of the case and weight it, it should not weigh less than 3lbs (1.4Kg), otherwise it is probably not adequate to meet the requirements of a modern system.

Also use the Google search box at the top of this page (enable the Web Search option on the first search page) to search for terms such as atx cases, atx + cases, pc cases, etc., or enter the make and model of known cases to obtain reviews and information about them.

Click Build Your Own PC for more information on cases on this site.

The better the quality of all of the components in a computer the less the likelihood of system failure. Of particular importance in this regard is the quality of the motherboard, case, power supply unit - and the heatsink and fan fitted to the processor, which should be checked regularly, because even quality units are prone to failure.

Some motherboards monitor the system's fans, and the processor temperature, and the BIOS setup can be programmed to produce an alarm if the fans fail and the processor temperature reaches a certain level. Even with a such a motherboard, you should still check the processor fan regularly just in case the monitors themselves are not working.

Low quality components almost always means trouble and expense sooner rather than later. Especially if you have to rely on the services of an expensive technician, etc. If, say, the power supply blows out, or fails while your hard disk drive is working, the chances of that drive being ruined are excellent.

If you are purchasing a new computer, or building your own, it would be worthwhile obtaining advice about the quality of the components from a respected source, unfortunately not usually the high-volume suppliers of computers. A small computer shop that has been in business for many years is usually a better source of information. It is also a good idea to subscribe to a good PC magazine, such as PC Pro (UK) and to visit a good online PC magazine such as PC Pro and Expert Reviews. There are also plenty of websites that provide this kind of information free of charge. You can make use of a search engine to conduct searches with suitable search queries.

Different uses can require a different style of case. Moreover, no single type or size of case has universal appeal. However, since they arrived on the scene many years ago, the mid-tower cases have been the most popular, probably because, for the vast majority of users, the purchase of a mid-tower case is the correct choice.

Removing an old power supply and installing a new one is a relatively simple task . You just remove four screws at the back of the case that secures the existing power supply unit in the case, remove the cable that goes to the motherboard and any of the components (hard drive, CD/DVD drive, graphics card, etc., take it out and then screw the new power supply in so that it connects to the same components. If you need instructions, here is a page that provides them:

Installing a power supply unit -

If you want to find out about the technical details of how a power supply works, visit this article. -

How Power Supplies Work -

See this page of the above article to view a table showing the range of the power requirements in watts of the main components in a personal computer. -

If want in-depth details of the specifications of a power supply, read this article:

Power Supply 101: A Reference Of Specifications [Dec 14, 2011] -

Power management

APM and ACPI are the two distinct power-management standards encountered when dealing with PC systems running Windows. The differences between the two standards can be confusing even to an unsuspecting troubleshooter who is fully aware of how often power-management issues can be the causes of system failures.

All computers currently have a BIOS setup program - usually entered by pressing the Del key after the start-up memory count - and most BIOSes have a page devoted to Power Management settings. Therefore, if you are experiencing problems that may be power-related, such as shutdown problems, the first actions to take would be to disable the power settings in Windows (in the Control Panel) and in the BIOS.

Superseded motherboards that use slotted processors

Thankfully, Intel and AMD no longer produce slotted processors (Slot 1 and Slot A respectively), because they are more difficult to install than socketed processors. As processors have increased in speed, they have become more difficult to keep cool. Socketed processors are easier to cool, so both AMD and Intel are now only using them. Still, it was an interesting period (1997 to 1999) having to install processors made by both of those manufacturers in a slot instead of a socket.

A boxed slotted processor will come with installation instructions, but if you buy a bare processor you will have to know how to install it.

Slotted processors come with two support arms that are already screwed into both ends of the processor's slot to support it in an upright position. They also either make use of a passive heatsink (no fan) that fits to one side of the processor's case, or a heatsink and fan unit that also fits over one side of the processor's case. Both units look like something dangerous.

Click the thumbnail image below to see a full-size image of an Intel Slot 1 motherboard with an Intel Pentium 3 processor that has a passive heatsink attached to it. - Use your browser's Back button to return here.

Click this thumbnail image to view a full-size image of an ATX Slot 1 Pentium 3 motherboard with a passive (no fan) heatsink attached to the processor

[Click to enlarge]

If (for some unknown reason) you need to find out how to install a Slot 1 (Intel) or Slot A (AMD) processor, try using a search engine. Try a search query such as: install + "slot 1" + processor.

A Slot 1 motherboard

Click the thumbnail image below to view the full image of an Abit BE6 Slot 1 motherboard fitted with 450MHz Pentium 3 processor. A heatsink and fan unit is attached to the near side of the processor, and the three SDRAM DIMM memory slots are fitted with 128MB PC100 DIMM modules. - Use your browser's Back button to return here.

Abit BE6 ATX Slot 1 motherboard, Pentium 3 450MHz processor, showing the heatsink and fan unit on the near side of the processor.

[Click to enlarge]

Note well

Note well that you should make sure that you purchase a cooling unit specifically made for the type of processor you are using. If a cooling unit is designed to be used with only one particular make or with both Intel and AMD processors, that information will be included in its list of technical specifications.

If you want to see which manufacturers produce quality cooling hardware, visit Click here! to go directly to cooling sites listed (on the third of four Links pages on this site) under Overclocking and Cooling Info Sites.

A motherboard always supports only a dedicated range of processors

Always remember that the motherboard must support a particular processor. For example, the Elite K7VZA motherboard (Elite Group), only has a 100MHz system bus (FSB) frequency, so it will only support the 100MHz version of the 1.2GB AMD Athlon processor. There is a 133MHz version of this processor that will run on Athlon-compatible motherboards with a 133MHz FSB frequency setting that is usually either enabled by setting the BIOS.

At one time, a particular Socket 7 motherboard supported processors made by Intel, AMD, and Cyrix/IBM, but now a motherboard only supports the processors made by a single manufacturer, with Intel and AMD being the two major manufacturers

Tip. - Take care when installing the heatsink and fan over a socketed processor. The processors look very solid and durable, but they can easily be cracked or broken by rough handling.

Software drivers: Updates

Updated software drivers for a particular chipset can be downloaded from the manufacturer's website (Intel, VIA, ALi, etc.), the motherboard manufacturer's website, or from sites that provide drivers, such as the list of them provided on the first Links page of this site.

These software drivers will be used to drive the system's IDE or SATA hard disk drives and CD/DVD drives, the PCI Express/AGP bus, and the USB Controller. They are frequently updated to make improvements and remove bugs, so it is well worth downloading and installing them.

There are occasions when a driver update causes more problems than the version it replaces, so it is always a good idea to read the postings in the motherboard's ALT newsgroup (more information is given about newsgroups further on in the article). Any difficulties experienced by owners of systems with your motherboard will come to light there in postings, and suggestions about what to do to remedy any problems will also be posted.

More relevant motherboard information

Disk-drive cables

Go to to read an article on the differences between the 40-conductor ATA 33 IDE ribbon cable and the newer, higher quality 80-conductor ATA 66 ribbon cable, which supports error correction, and can be used for any ATA hard drive, including ATA 33 and ATA 100 hard disk drives - even if that drive does not support error correction.

See this page of the Build a PC article on this site for information about the new round IDE cables.

Click here! to go to information on this site on the new serial SATA disk-drive standard, including images of the cables that it uses.

Motherboard ports

The motherboard itself will usually be fitted to a removable tray fixed up against one side of an ATX tower case in one way or another, so that the adapter/expansion slots are properly aligned with their outlets at the back of the case. Because expansion/adapter cards are fitted at right angles to the motherboard, the rectangular ports to which the peripheral devices, such as the monitor, are attached, will be horizontally aligned at the back of the case.

Many motherboards coming out now have done away with all of the legacy ports (PS/2 mouse and keyboard ports; parallel port, etc.), and have replaced them with USB and FireWire ports.

The ATX Abit AT7 motherboard - available on both the Athlon (Socket A/462) and Pentium 4 (Socket 478) platforms - is such a motherboard. The ports on the motherboard are shown in the image below. -

The ports panel (I/O panel) of an Abit AT7 motherboard

From left to right are the two USB 1.1 ports, two USB 2.0 ports, a pair of IEEE1394 FireWire ports, full analog 5.1 audio out, digital audio out (five round and coloured ports), and LAN (network) ports (far right).

There are no legacy ports, so, with this motherboard installed, unless you obtain conversion plugs that are available (see the USB page of this site for images of them and more information), you would not be able to use a printer that only has a parallel port, a PS/2 mouse or keyboard, a serial external modem, or any device such as a joystick that uses a serial port. You can only use USB or FireWire devices.

Below is the ports panel of a motherboard with USB and FireWire ports that retains PS/2 mouse and keyboard ports (far left), the parallel port (red), and, below it, a single serial port. The round coloured ports belong to the incorporated sound chip, and the two blocks on the left and right with three ports each incorporate a single FireWire port each (top), and two USB ports.

The ports panel (I/O panel) of a motherboard with some legacy ports

As shown in the images at the beginning of this article, ATX cases are fitted with a removable ports panel that often has metal cut-outs in it that are themselves removed so that the ports on the motherboard fit through them. You remove the cut-outs in the ports panel that match the ports on your motherboard. For instance, you would not remove the cut-outs for an inbuilt video card port or for a sound card's ports if the motherboard does not have inbuilt video or sound ports. The ports panel that comes with a new motherboard usually doesn't have the openings for the ports covered with cut-outs, because all of the ports on the board match the openings on the ports panel, so that no holes will be left that might reduce the cooling of the inside of the case.

As you can see, the Abit AT7 motherboard has a port profile that is completely different from the standard ATX legacy motherboard's port profile shown above it. Luckily, this motherboard comes with a ports panel that matches its unique port profile, but that might not be the position with other motherboards - especially if purchased second-hand. In that situation, you would either have to buy a case that comes with a port face plate that matches the motherboard's port profile, or you would have to install the motherboard with the port face plate removed. So, always check the position regarding the ports panel before you buy a motherboard.

Views of the case, a processor socket, jumpers, and DIP switches

Note that most recent motherboards make minimal use of jumpers or DIP switches (explained further down in this section of the page) to configure the motherboard's FSB, processor, RAM settings, etc. Where jumpers are used, they usually only perform functions such as clearing the BIOS password, or clearing the BIOS setup program itself so that the default settings are returned when the computer starts up. The customisable configurations are enabled or disabled in the BIOS.

Showing the back of a standard ATX case

[Click to enlarge]

Showing a close up view of the outlets for the expansion cards


The thumbnail images above are views of a desktop tower computer case. The large vertical slot on the case, above the horizontal slots, is the cutting for the ports built into the motherboard. The motherboard itself will be fitted along the right side of the case. This is a standard ATX case that will accept standard ATX motherboards. If it was a case that was made for motherboards that use a riser card (fitted in a slot at a right angle to the motherboard) to fit adapter cards, the adapter slots (fitted at right angles to the riser card) would be vertically instead of horizontally aligned at the back of the case.

The use of a riser card makes it possible to use a case that is much slimmer than a standard ATX case. Indeed, it is almost certain that slimline desktop and tower cases have to be fitted with a riser card.

There is information further down on this page about why non-standard ATX cases and motherboards that make use of riser cards should be avoided.

A Super Socket 7, AT form-factor motherboard - now superseded, but still in use, which uses Intel MMX, AMD, and Cyrix/IBM processors, differs from a Slot 1 motherboard for (Pentium II and III CPUs) in having a large square, usually white, ZIF Socket for the processor - and the Level 2 cache chips on the motherboard itself instead of being built into the processor's case.

FIC VA 503+ Super Socket 7 motherboard

[Click to enlarge]

Close-up view of a Super Socket 7 motherboard's processor socket

The motherboard shown in the thumbnail image (above left) is the VA-503+ from FIC, a Baby-AT form-factor, Super Socket 7 motherboard, with a VIA Apollo MVP3 chipset, that can be powered by Intel MMX, Cyrix/IBM M1/M2, and AMD K6, K6-2, and K6-3 processors. Baby-AT boards are housed in AT cases that have been superseded by ATX cases. The white ZIF (Zero Insertion Force) processor socket is in the bottom left-hand corner of the motherboard, as shown in close-up in the image on the right, in which the brown insertion/extraction lever is more clearly visible down its left-hand side. The VIA MVP3 chipset, consisting of two chips, can clearly be seen above the ZIF Socket, with the BIOS chip's battery between them. An Award flash BIOS chip with its silvery sticker can be seen in the upper left-hand corner of the board. There are three black ISA slots, three white PCI slots, and an AGP slot next to the last PCI slot.

On this motherboard, the banks of configuration jumpers can clearly be seen coloured blue.

Block of jumpers used to configure the hardware settings on some motherboards

[Click to enlarge]

DIP switches used to configure the hardware settings on some motherboards


The two thumbnail images, above, which show DIP Switch blocks on a motherboard (right), sometimes used to configure its settings, and a block of jumpers (left), which are found on most motherboards, including those that make use of the BIOS setup program to set the hardware configurations. You should be able to find out how to place the jumpers and set DIP switches in the motherboard's manual.

The proper support considerations when evaluating a motherboard, either in a new computer, or as an upgrade

The selection of a motherboard can have a marked effect on a PC's reliability. The motherboard can be the difference between a stable, reliable machine, and endless crashes.

By becoming familiar with the different parts of a PC's hardware and software, you will easily be able to make an informed choice. This site contains all of the information in the form of articles or links to other information that you will need to gain that knowledge. My advice is to keep reading until everything falls into place of its own accord.

I am assuming that you are building your own computer or upgrading an existing one. The questions you need to find answers for are as follows:

1. - Does the motherboard support the type of processor (Intel or AMD) and RAM that you want to use? And does the form-factor of the case match the form-factor of the motherboard?

For example, a standard ATX AMD Athlon motherboard can be installed in any standard ATX case, but a specially designed ATX case is required for a Pentium 4 motherboard.

If you are upgrading a brand-name PC, you might only be able to install a customised non-standard motherboard in its customised non-standard case. The manufacturer might be able to supply the upgrade. If not, you will have to buy a standard case and motherboard.

2. - Does the motherboard's manufacturer have a website that provides BIOS and device driver updates, which is frequently updated to cover other support issues, such as operating system, hardware, and software compatibility?

Visit the BIOS page of this website for information on the BIOS setup program.

Hardware includes, RAM (SIMMs/DIMMs/RIMMs), hard disk drives, ports (serial/parallel/USB/FireWire), video cards (ISA/PCI/AGP), etc.

For example , most hard disk drives purchased new now use the IDE ATA (UDMA) 100 or 133 mode, while the BIOS and motherboard's chipset might only support ATA (UDMA) 33 or 66 modes, perhaps making it necessary to install a software patch from the drive's manufacturer to disable ATA (UDMA) 100 mode so that the UDMA 33 (or 66) mode can be used instead. But, most of the time, all you have to do is install any ATA (UDMA) drive to a motherboard that supports any ATA mode, and it will work at the highest mode supported by that motherboard and operating system, even if the drive itself can work in an even higher mode, such as ATA 100 or 133.

The first FAT16 version of Windows 95 only supports hard drives and drive partitions of 2GB.

3. - Is the power supply unit (PSU) adequate to power the devices being installed, or to accommodate upgrades?

For example, emachine PCs usually have very low-powered power supplies that are barely adequate to run the hardware, which usually have their video and sound chips incorporated on the motherboards. You would not be able to upgrade to a video card without also replacing the power supply.

For more information on this site about the three main modes of operation of hard disk drives (SATA, IDE (also known as PATA), SCSI/SAS), click Disk Drives.

USB/FireWire support

Note that, depending on your requirements, you should also know about USB and FireWire support in order to make the best choice of motherboard.

The settings

The motherboard settings shown below, set either via the BIOS setup program, or by jumpers or DIP switches on the motherboard itself, should be indicated and explained in the motherboard's user manual, which is provided with a retail, boxed motherboard, or can usually be downloaded for inspection from the manufacturer's website.

AMD's K6-2 and K6-3 ranges of desktop CPUs are no longer being made. (Visit for information on the latest AMD processors). But I am still using them to illustrate processor settings here, because even though the clock-multiplier settings are usually fixed on the latest processors so that specific knowledge is required to change them for overclocking purposes, the settings themselves remain the same.

To understand how the processor and memory speeds are determined, you have to understand what the Front Side Bus (FSB) is.

Note that the latest AMD and Intel processors use the HyperTransport and QuickPath Interconnect buses respectively instead of the FSB.

Front-side Bus -

"The front side bus as it is traditionally known may be disappearing, but it's still being used in all of Intel's Atom, Celeron, Pentium, and Core 2 processor models. Originally, this bus was a central connecting point for all system devices and the CPU [processor]. In recent years, this has been breaking down with the increasing use of individual point-to-point connections like AMD's QuickPath Interconnect. The front side bus has been criticized by AMD as being an old and slow technology that bottlenecks today's computer systems. While a faster CPU can execute individual instructions faster, this is wasted if it cannot fetch instructions and data as fast as it can execute them; when this happens, the CPU must wait for one or more clock cycles until the memory returns its value. Furthermore, a fast CPU can be delayed when it must access other devices attached to the FSB. Thus, a slow FSB can become a bottleneck that slows down a fast CPU. FSB's fastest transfer speed is currently 1.6 GT/s, 3 to 4 times slower than current QuickPath Interconnect speeds and 2 times faster to 2 times slower than HyperTransport speeds." -

Front-side Bus -

HyperTransport -

Intel QuickPath Interconnect -

In the UK, provides processors and other clocked PC hardware that has one official speed, but is guaranteed to function perfectly well at an overclocked speed. Where the clock-multiplier has to be altered on the CPU manually, this will have been done for you. For example, a processor with one officially guaranteed manufacturer's clock speed, will be guaranteed to function at a much higher clock speed, and come with a reduced price compared to the processor that is officially guaranteed to run at that speed by the manufacturer.


CPU Core Frequency

CPU Core Voltage

Motherboard I/O Voltage

M/board Bus Speed (FSB)

M/board Clock Multiplier Setting

AMD-K6-3 500





5x - CXT core

AMD-K6-3 450





4.5x - CXT core

AMD-K6-3 400





4x - CXT core

AMD-K6-2 550





5.5x - CXT core

AMD-K6-2 500





5x - CXT core

AMD-K6-2 475





5x - CXT core

AMD-K6-2 450





4.5x - CXT core

AMD-K6-2 400






AMD-K6-2 380






AMD-K6-2 366






AMD-K6-2 350






AMD-K6-2 333






AMD-K6-2 333/66






AMD-K6-2 300






AMD-K6-2 300/66






AMD-K6-2 266






AMD-K6 300






AMD-K6 266






AMD-K6 233

233 MHz





AMD-K6 200






AMD-K6 166






The speed of a processor (the core frequency) is the product of the motherboard's front side bus (FSB) speed/frequency, and the clock-multiplier setting. The FSB is the the network of connections on the motherboard that run between its devices and chips, and the FSB speed/frequency is the frequency measured in MHz that it is set to run at.

See the RAM page on this site for information on how the FSB relates to the effective, as opposed to the actual speeds at which DDR RAM runs.

The I/O voltage is fixed and is usually unchangeable.

The variable core voltage can be set according to the requirements of the processor. On reputable motherboards, the range of settings can usually be altered in increments of .1 of a volt. The latest Intel and AMD processors use less voltage than the K6-2 and K6-3 processors, because the latest manufacturing processes can put more circuitry in much less space, but they use more power because they work at much higher speeds/frequencies. That is why cooling and protection from overheating is of such importance now.

Poor or cheap motherboards can come with very limited settings for bus frequency, the clock multiplier, and the core voltage. That is why it is very important to find out what the range for each is before you buy a new computer or motherboard. Small increases in these settings can often cure an unstable system. This can be done by implementing the settings' information in the motherboard's manual.

AMD tests all of the most popular motherboards that have been designed to run AMD processors. The tests focus on three major areas of motherboard processor support: the BIOS, electrical, and software. A motherboard is only listed on the AMD's recommended motherboard list after it has passed all of the tests. Although there may be motherboards not included on this list that may function perfectly adequately with an AMD processor, AMD only recommends the designs that have been fully tested and passed by the company. You can find links to recommended motherboards on AMD's home page at

Note that Intel's Pentium 3 and 4 processors, and the AMD Athlons and Durons, usually, but not always, have an onboard clock-multiplier that can be changed, but only by someone who knows precisely how to do it.

Toms Hardware has an illustrated article on how to unlock the clock multiplier by using a pencil on AMD Athlon and Duron processors.

The only easy alternative way to overclock those processors is to use a faster bus frequency (FSB) setting - from using the default of 100MHz to using, say, 112MHz or 133MHz - if the motherboard supports the faster speed.

You should be able to find out everything you need to know about its settings and how to overclock a particular processor from

Take care! Gather all of the necessary information before you attempt any kind of overclocking. You can destroy a processor, and other hardware, if you take the settings too far over their default values.

Note that some motherboards are more overclocking-friendly than others, and some motherboards might not allow overclocking at all. Overclocking involves increasing the bus frequency (FSB), or increasing the clock-multiplier setting.

The following quote from the article above provides the reason why you usually have to choose a suitable motherboard and memory combination in order to overclock successfully.

"Some motherboard vendors don't lay out their products to use very fast DDR2-1066 RAM; the reasons for this have to do with the components they choose to populate their boards. These must be of higher quality to deliver clean signals to memory at such high speeds, which makes motherboards more expensive. Even printed circuit board designs play a significant role: data lines designed to run at 500 MHz can be placed very close to one another with lengths of up to almost 4 inches (10 cm). A bad design can cause capacitance build-ups and resonance to develop among circuits, which in turn can cause instability or crashes when clock rates are cranked up."

The web search query beginners guide to overclocking provides links to plenty of articles. Here are a few links that I found:

If the information in this four-page article on motherboards, cases and power supplies has provided you with sufficient information on how to choose a suitable motherboard, try using a search query, such as guide to choosing motherboard. There are many guides, many of which are quite old, such as the PC Guide's guide that dates back to 2005 but which still ranks high in the search results in Bing and Google. If you want a motherboard that allows a wide range of overclocking settings, try a search such as: best overclocking motherboards.

Future-proofing your investment - the considerations

For the maximum future proofing, it is therefore of the utmost importance for everyone to know the make and model of motherboard a computer has before purchasing it.

If you have access to the Internet, valuable information can be gleaned about motherboards from PC hardware sites, such as Tom's Hardware Guide. If you don't have Internet access, it would be well worth your while to make use of an Internet cyber café to access this information. If a computer manufacturer's site doesn't provide the make and model of motherboard in a particular model of computer, you should be able to send in an e-mail request for the information. Obtaining a Hotmail e-mail account would be the best way to do this if you're using a cyber café.

Beware - many of the computer suppliers that advertise in newspapers and magazines often use cheap or no-name or old or integrated motherboards, which have very limited upgrade potential. That is why they don't name the motherboard in their advertisements!

Slimline desktop, and mini tower cases, or proprietary-make tower cases that use riser cards to attach sound, video, adapter, and modem cards parallel instead of at right angles to the motherboard, should also be given a wide berth.

Slimline and mini-tower cases severely restrict the expansion of the computer, and proprietary makes of case that use a riser card to attach expansion cards have specially designed motherboards which usually only that particular manufacturer will be able to replace - usually at a premium. At a future date, you will therefore not be able to install any of the much wider range of standard ATX motherboards.

Click here! to read about the low-profile video cards installed in slimline desktop cases that can be used by HP, Compaq, and Dell. Use your browser's Back button to return to this point on this page.

Whether or not a computer has a motherboard that uses a riser card can be determined from looking at the back of a tower case. If the rectangular attachment ports at the back of the case - the plug-in points on the backing plates of the ISA or PCI or AGP expansion cards - are horizontally aligned the computer has a conventional ATX motherboard. However, if all these ports are vertically aligned, then the motherboard uses a riser card. The case will usually be small and/or slim.

Do not buy a computer that has this kind of architecture unless you have no intention of upgrading it.

Note that the alignment will be the opposite of this on desktop cases, with a vertical alignment of the attachment ports indicating a standard motherboard. This is because the motherboard is fitted to the bottom of the horizontal case, and the ISA, PCI, and AGP cards are fitted at right angles to the motherboard, so the ports on the cards will be vertical.

All of this might sound complicated, but all you have to do is imagine how the motherboard fits vertically along one side of an ATX tower case, with the expansion cards at right angles to it. A riser card fits at right angles to the motherboard and the expansion cards are fitted to the riser card, at right angles to it, thus making them lie parallel to the motherboard so that their rectangular ports are vertically aligned.

You can easily work out the alignment of the ports on a desktop case, because a desktop case is really just a tower case lying on one side with the motherboard screwed to the bottom side.

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