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Computer power supply units deliver the power to the PC hardware through a number of cables with connectors, the number of which depends on the type and output of the power supply itself. However only the number of the connectors changes; in order to ensure compatibility, the type of the connectors used per generation is identical. The generic specifications for various PSU form factors are defined in Intel's design guides, which are periodically revised.
The largest and most important connector is the ATX 24 pin Molex main connector. As the name implies, it has 24 pins which carry all of the output voltages, several common (ground) pins and even some signal pins (such as the “Power OK” signal). The exact pinout diagram of the ATX 2.X connector can be seen below. You will notice there is a blank pin (N/C), which used to be the -5V line and has been removed from the 2.X standard. There is always only one ATX main connector.
CPUs nowadays require a lot more power than some years ago, therefore power connectors dedicated to CPU power became necessary. Most low and middle range motherboards use a P4 ATX connector, seen at the schematic below, theoretically able to provide up to 192W worth of power to the CPU. On high performance motherboards this connector has already become obsolete and they are using the 8-pin EPS connector instead, which is twice as large as the P4 connector and can supply the CPU with twice as much power.
The EPS connector started as a server/workstation motherboard component but with time it became a necessity to satisfy the ever rising power consumption needs of modern CPUs. Most EPS connectors (also called 4+4 pin connectors) can be split and used with motherboards using a P4 connector. Home consumer power supplies always have only one EPS/P4 connector.
The ever rising power consumption is not a problem related with the main CPU only; during the past few years a great deal of video cards consume great amounts of power. This has led to the addition of another connector, the PCI Express (PCIe) 6 pin connector, able to feed a PCIe video card with up to 75W.
The power demands of some of the video cards would soon lead to the release of the PCIe 8 pin connector, which is able to transfer twice as much power. Even then the power consumption of some video cards could not be satisfied and it is not uncommon to see more than one connector on several of the latest high performance video cards. Latest computer PSUs should have at least one 6 pin PCIe connector but as their power output increases so does the number of the PCIe connectors they offer.
SATA was introduced to upgrade ATA devices to a more advanced and efficient design. Almost all SATA devices, usually hard disk and optical drives, require a SATA power cable. The few exceptions are the early SATA devices which had 4-pin Molex connectors for compatibility with the power supplies at the time they were released. The number of SATA connectors depends on the type and output of the power supply alone, ranging from none to tens of connectors.
The 4-pin Molex connector is by far the most popular connector in the history of computer power supplies. It has been in use ever since the first implementations of switching PSUs designed for personal computers and it still is a very common connector, despite the introduction of the SATA connectors a few years ago. 4-pin Molex connectors are being used to power almost everything inside a PC, ranging from drives and fans to providing supplementary power to special motherboards and devices. The number of 4-pin Molex connectors depends on the type and output of the power supply alone, ranging from a mere couple to tens of connectors.
The 4-pin Berg connector was introduced when the first 3.5″ floppy drives started showing up, which is why it is also called a floppy connector. Although some late AGP video cards also used Berg connectors for extra power which the AGP slot could not provide at the time, the Berg connector never became as popular as the 4-pin Molex connector. At this point of time it is slowly being phased out, following the disappearance of the 3.5″ floppy disk drives. Most recent computer PSUs have only one or two Berg connectors at most.
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Bloody Nora IronLaw, that certainly is detailed. I made it to page 2, now I need a glass of coke (cola not powder). I shall return later once I absorb the basics !
I am one of the most demanding readers on the face of the planet. The standard of editorial content on this site is without a doubt leading the way on the net right now. Some of the news stories are very ermm interesting, but the reviews are fantastic.
I have bookmarked this, I shall spend a few hours Sunday afternoon chilling and trying to work this out. I need to read this at a snails pace to get to grips with it all.
Well this is taking power supplies to the next level. I got lost in parts, and im quite technical, but its well written and rather complex. Nice idea these articles, at least you guys expect the readers to know more than the usual tech site reader
Thank you, thank you , thank you.; I always wanted something like this, with images and easy to understand text. I have struggled on page 4 and 5, but I have picked up more from this than any other PSU related article on the net.
A hell of a lot of work in this Ironlaw. Thank you very much for making all this effort to educate us peasant mortals π
brain overload………… ekkk.
I am just too stupid to understand half of this, but thanks anyway ! the last page was as far as I made in understanding it all :p
Stunning work IronLaw, technically way above my level, but I feel a little better for having read it. I love the PSU reviews on KitGuru too. at the same level as Hardocps (which are also excellent).
With standard of content like this on a regular basis, you will go far ! top marks KG
Christ on a stick. lost for words. This is more for apprentice engineers !
Normally I see these guides and think, oh here we go again, some idiot reviewer ranting on about something stupid and trying to understand it himself.
Not in this case. Ironlaw is a cut above! really really enjoyed this one.
**claps** – I understood most of it, which is surprising as I only know the basics about power supplies. I hope to see more of these. I would like one explaining what exactly we need to buy when looking for a PSU, single rail 12v? multiple rails. and making sense of actual ratings. who needs 1200W psus for instance? do we ?!
Well that was surprising. very very good reading. bit complex for me in parts, but I picked up bits and pieces.
Ironlaw, thank you. very informative reading for a friday morning π now off to work to type in numbers.
lol, I just read something so badly written on bittech, then I come here to read this. its like comparing nickelodean to the discovery channel.
I feel educated, thank you π
For such a complex article it is very informative, a little complex for this geek, but im sure many people love all this about PSU’s. The last page was helpful :p
I shall email Zardon for permission to use parts of this for an edu guide I am writing for college kids.
Brilliant piece of work. 10/10
I find power supplies totally confusing. I just buy one and get a good one after reading several reviews online. I actually ordered the thermaltake one after reading the review on kitguru. This was educational but honestly a little over my head for 70 percent of it. I learned a little, which is more than I normally do every day !
Fantastic writing and very educational as other people have said. I read the power supplies reviews here in the last month and I prefer them to johnny guru. Johnny is great with PSUs but his writing style annoys me, jokes are fine, but half the review is him trying to be funny. The reviews on this site are just as detailed but more focused. I hope you get the corsair 1200w PSU to review, I want to order it, but its 260 here and im not sure if its worth it.
read it in detail – very good work indeed Ironlaw, you know your work π
My brain hurts.
Where do i find the for dummies version?
Nice work mate π
Cool and easy to understand