By Joel Hruska
Date: November 30, 2001
Back when the P4 came out it was widely publicized that Intel had made a few changes to the ATX standard-and that P4 systems would require an additional power cable. There was some grumbling about this at first, but the cable was inserted into the standard to add stability to the total platform-and with system power demands rising fast, it's a move that made sense in the long run.
In July I bought an Enlight 7237 case with a 300-watt power supply that claimed to be both AMD and P4 compatible. Sure enough, when I checked the PSU, there was an extra 1x6 adapter that I hadn't seen before. I assumed this was the power connector in question that I'd heard about months earlier, and didn't give it another thought.
About two weeks ago I was working on a P4 system, however, and noticed that the 350-watt Enermax PSU I was using had the 1x6 Auxiliary Power Connector (as Intel calls it) but also had another 4-prong adapter. My Enlight supply lacked this cable-but both supplies were advertised as P4 compatible. Since I was curious about this point I got in touch with George Alfs at Intel, who was kind enough to provide me with the following information.
The 1x6 Auxiliary Power Connector is in place to provide support for AGP Pro 50 cards. Because AGP Pro 50 cards require more amperage than the ATX standard is designed to deliver, the Auxiliary Power Connector delivers an additional 12 amps to bring the total available to thirty. This cable, according to George, is not necessary if a board does not support the AGP Pro 50 standard.
This, however, is not the cable that makes a PSU
P4-compatible or not. It's the other cable-the cable my Enlight lacked-that
makes the difference. The 4-pin cable is a +12V cable, designed to deliver
additional current to the motherboard. This, according to Intel, enhances
platform stability and flexibility.
Now, I know it IS possible to run at least the MSI Pro 5 i850 motherboard
without this 12-volt connection, because I ran the board in this fashion for a
week and had no problems with it. On the other hand, however, a link on Intel's
website prominently states that i845 motherboards will NOT function without the
additional power connectors:
http://support.intel.com/support/motherboards/desktop/D845WN/power_supply.htm
Information on the i850 board's power requirements is available here - note that
the i850 webpage lacks the warning about the 12-volt connector.
http://support.intel.com/support/motherboards/desktop/d850gb/tti002.htm
I'd definitely recommend only using a PSU with a +12V connector, even if your P4
motherboard will function without one. Improper or irregular power support is a
VERY effective (and expensive) way to kill computer equipment [ed: in most
cases, your system will simply not boot because the current the P4 demands may
pull down voltage too far at startup].
Intel took a fair amount of flak for their decision to revise the ATX power
supply standard (P4-compatible supplies are called ATX12V instead of simply ATX).
The fact is, though, the original ATX standard was developed back in 1996 when
computer's had vastly different power requirements than today's machines.
Inevitably, standards must be re-evaluated and upgraded in order to remain
effective. Roughly a year later, most PSU's are shipping both Athlon and P4
compliant, making this a non-issue for new buyers.
Just remember if you're looking to get an i845 DDR motherboard, make sure that
your power supply has the extra 12-volt cable. Otherwise you'll end up with a
non-bootable board-and quite a headache.
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