Motherboard voltages

[kdrew098]

I know that most data travels around the motherboard and other devices on +5vdc and that +3.3vdc which was at first primarily for cpu's and is now used for many AGP, PCI devices and DIMMs. It's also obvious that the higher voltages +12vdc are used for mechanical devices like disk drives. What is the significance of the -5vdc and -12vdc? Why are these voltages necessary?

I am going to begin learning more electronics in the near future, but in the meantime, I haven't found a detailed schematic out there that includes the exact voltages on various lines of the bus. This might help.

Since getting laid off as a programmer a year ago, I have been an A+ instructor. There are technical details that I really want to understand for which I can find no information in books or manuals. This information is not necessary for my students but I would really like to understand as much as possible.

I've never claimed not to be a bit obsessive. Thanks for any help!
Kevin Drew

[AllGamer]

now that you mentioned you did raise quite an interesting question.

i do also wonder a couple of times about those -# voltages. Just never kicked in, since i never had to repair a mobo in a long long while.

got too lazy after knowing that now in days you can just send the board to RMA.

back then in 486 and early P times, yeah rite, for a RMA to occur you had to have a miracle happen to you. ;)

so yeah back then i did repair quite a bit of mobo and all kind of other electronics.

but since 99.9% of the time was simple stuff, never had to really refer to an schematic. :t

i'll see what i can dig up :)

[kdrew098]

Thanks, any information you dig up would be great. In the meantime, I'm going to continue to dig around. One thought is to look at the pin-outs for the various expansion slots and try to figure out which ones are used for what.

KD:t