CODEWITHSUNDEEP
assemblynasmbootloaderreal-mode
vakus
vakus

Reputation: 740

bootloader reading drive parameters

I want to get dimensions of hard drive. I find that I need to use int 13h with ah = 08h. I found on wikipedia that it returns following:

DH logical last index of heads = number_of - 1 (because index starts with 0)

CX [7:6] [15:8] logical last index of cylinders = number_of - 1 (because index starts with 0)

[5:0] logical last index of sectors per track = number_of (because index starts with 1)

The problem is that I have no idea how to read only bits [5:0] on it own to get last index of sector per track, and the same with [7:6][15:8] to get last index of cylinders. I would be really thankful if someone would point me into the right way or explain how to do this.

Upvotes: 1

Views: 115

Answers (1)

Sep Roland
Sep Roland

Reputation: 39166

mov  ax, cx
and  ax, 63
shr  cl, 6
xchg cl, ch

This leaves sectors in AX and cylinders in CX

Upvotes: 2

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