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Re: Bootloader - the first 512 bytes

From: Narcis Garcia
Subject: Re: Bootloader - the first 512 bytes
Date: Tue, 9 May 2023 08:21:39 +0200

As I read from Peter Norton's IBM developer guide (1985):

Care of 4x16 reserved bytes for MBR partition table. Those 64 bytes begin at position 1BEH in case of MBR format.

El 8/5/23 a les 20:37, Gijs Slijpen ha escrit:

For a while now I have been trying to get a boot loader written in Assembly to work on a 
Dell Gateway 5000 and a Dell Latitude 5590 both have intel i5 processors. My boot loader 
is a simpel one: it outputs the words "Hello World" to the screen. The code 
works in a virtual machine that I have set up in Virtual Box. However, when trying it out 
on a both of the machines mentioned before only “Hell” is being printed (maybe my 
computer is trying to tell me something).

I figured out that if I use some padding in my boot loader right after the 
first command (for example defining 24 bytes of 0) and then continue my code 
the boot loader actually works on both my Dell machines but I do not know why. 
Then, just today, I thought I’d have a look at the Grub boot loader boot.S file 
to see whether I could get that to work on my Dell machines. Funny thing: I 
found there are 25 nop’s in there right after the first instruction.

Would anyone maybe care to explain why this is? I have been looking around and 
not been able to find any documentation on this yet, there is a chance that I 
will find it in Intel’s software development manual but I thought I’d also ask 
it here.

I am looking forward to a reply.

Thanks in advance!

Best regards,

Gijs Slijpen

Narcis Garcia

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