Newsgroups: comp.os.minix
Subject: Re: bootblock.s
From: bmarcum@iglou.com
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Date: 27 Oct 2000 17:57:22 -0500
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On 2000-10-26 @cisco.com said:
   >Hi all,
   >I am trying to understand the bootblock.s code in /src/boot
   >directoty. I have a couple of questions related to this:
   >1) When the BIOS is done with its work, it copies the bootblock
   >from the booting device (floppy or hard disk) into RAM and jumps
   >there (0x7C00). What is the state of the registers at this point ?
   >As far as i know, the state is
   >DL = Boot drive, 1h = floppy1, 80h = primary harddisk.
   >CS = 0
   >IP = 0x7c00
   >What about other registers (including segment selectors/registers
   >like FS, GS etc etc) ?
Undefined.  The boot program has to set whatever registers it needs.
   >2) The code seems to be reading some hard disk/floppy disk
   >parameters. What are these parameters ? Why is this necessary ? and
   >where are they stored ? Are they burned into the hard disk/floppy
   >disk ??
Which parameters are you referring to?  Some may be in the boot sector, others
in CMOS memory.  In order to read a hard disk, the boot loader must know
how many heads, sectors per track, and cylinders the drive has (newer drives
can use LBA, but the OS must be compatible with older hardware).

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