jaypee68@gmail.com wrote:

> I have an older power supply with a -5v rail and an MSI K7N2-6570
> motherboard. With this combination, the BIOS shows voltage on the -5v
> rail, but if I put in a different power supply that doesn't even
> support a -5v rail, I get 0.00 voltage in the BIOS. I know what you
> are probably thinking, "duh! of course you won't see voltage if you
> don't have the -5v rail.".
>
> My question here is, if my newer power supply doesn't support the -5v
> rail, and the motherboard is expecting it, will I have any problems?
> The system ran fine through POST, and memtest x86, but it wasn't kept
> on for much longer after that. What would the motherboard be
> utilizing a-5v rail for? Will the motherboard malfunction without
> this -5v rail? Any chance of damaging anything by not supply this -5v
> rail?

Some old MBs or ISA cards required -5v. It was removed from the ATX PSU
specification in 2002. Read:

http://www.playtool.com/pages/psurailhistory/rails.html