This isn't really coding-related, but it is computer related:
On seemingly every new workstation, desktop, and server, Dell includes four little LEDs somewhere on the case labelled A, B, C, and D. Does anybody know what they do? I think they are diagnostic-related, but I'm not sure.
A: Floppy 1, B: Floppy 2, C: Hard drive and CD-ROM. In the next version, the LED's will attempt to properly rename themselves if you for some reason remap the partitions and hard drives (but this is of course for advanced users only!) - but since LED's E through Z don't exist your computer will crash hard, and your data will relocate into cyberspace.
Google holds the real answer though. In the first found page, it's all available for Reading in The Fine Manual.
They are diagnostics, but I suggest searching google for better answers.
Yeah, they actually are used for error codes for when your comp wont start. Different combinations are used to indicate what went wrong -- mainly to help smooth out tech support, I beleive. The Dell PC owner's manuals sometimes contain a listing of the codes.