BIOS interrupt initalization

[eliscool]

Could someone please tell me what all the registers are initailized to but the BIOS (for your bootsector)? like DX is highbyte = ??h, lowbyte = drive num we booted from right? im pretty sure CS, DS and SS are set to 00h, but what is SP set to? is it 'valid' memory?

[Pype.Clicker]

don't be sure of CS and DS : they could be 0x7C0 on some BIOSes.
SS:SP is "guaranteed to be some valid stack " (big enough to handle BIOS interrupts, imho) but you have no guarantee of how big it is, thus if you have function calls, you should better set up a new stack.

[eliscool]

any of the other registers have useful stuff in them? (eg. like dl has the drive num)

[Pype.Clicker]

not to my knowledge