The motherboard power supply is the replaceable unit inside a computer that supplies power to the system. Also known as a power supply unit (PSU), it provides cabling that runs from the unit to the power switch on the case, motherboard, drives, graphics card, and fans. The power supply also incorporates a fan to cool the unit, which can come out the back, bottom, or top, depending on the model.
A computer motherboard.
As motherboards have evolved over the years, so has the power supply. In 1995, the ATX (Advanced Technology eXtended) form factor was released, replacing the earlier AT motherboard and power supply standards. ATX remains the most common form factor, spanning multiple versions that represent evolving standards. While many years ago it was easy to buy an ATX power supply for an ATX motherboard, things have gotten a bit more complicated.
A power supply supplies power to the motherboard and other computer components.
In addition to the alternate connectors used for newer Serial ATA (SATA) drives compared to legacy Parallel ATA (PATA) drives, and the ability to run dual graphics cards to get more gains for your games, the way the motherboards base use energy also changed. Newer motherboards use a 24-pin main power cable, while older motherboards use a 20-pin cable. Some power supplies come with a 20+4 connector that splits to fit any type of motherboard. An adapter can also be purchased to convert one type of connector to another.
In the past, the main power cable was used to power the computer’s processing unit (CPU), but today virtually all motherboards use a dedicated 12-volt CPU power cable. Here again, there are two standards or versions: the 4-pin connector (P4) and the 8-pin connector (ESP12V). In addition to the main power cable, some motherboard power supply models come with a 4+4 12V CPU cable to fit any type of motherboard, or an adapter can be used.
If you are working with an older AMD® dual CPU motherboard, a 6-pin auxiliary connector may be required. Most power supplies do not provide this cable, so if your motherboard requires it, you can purchase a compatible power supply.
Older computers draw power from the 3.3 and 5 volt rails provided by the motherboard’s power supply unit, but with the introduction of the AMD® Athlon 64 and Intel® Pentium 4, a new strategy emerged that uses the 12 volt rail. As a result, PSUs that follow the ATX12V 2.0 (or later) standard direct most of their power here. If you’re buying a power supply for an older motherboard that’s based on the 3.3/5 volt rail, consider a motherboard power supply made to the ATX12V 1.3 (or earlier) standard, which provides the most of its power to 3.3/5 volts bus. Alternatively, some newer power supplies provide enough power on the 12 volt and 3.3/5 volt rails to be compatible with any motherboard.
The number of connectors or cables on the PSU is an important consideration. Some cheaper models have fewer connectors, which may work for some systems but not others. Also, modular power supplies are usually a bit more expensive, but allow the user to plug in only the cables needed, avoiding the clutter of extra cables inside the case. However, some enthusiasts shy away from modular designs, believing plug-in connections to be a potential source of unstable power supply, unlike corded models.
Another consideration when looking for motherboard power supply is wattage. There are several online calculators available to get a general idea of what range to consider. The average system with a single graphics card is generally well served by a power supply in the 550 to 650 watt range, but your mileage may vary. Also be sure to check your motherboard specifications or manufacturer’s website for wattage recommendations, as a particular number of amps may be required as a minimum on a particular rail.
Not all motherboard power supply units are created equal. Some provide cleaner power, while others can be made with second-rate components. When checking specifications, compare supported or tested hardware, efficiency ratings, certifications, and warranties as some indicators of quality. Customer reviews can also be helpful.
The motherboard’s power supply runs from the drive to the computer’s power switch.
