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Assistance with Code

Comment a comment by Matthew Vea (VnutZ), published on 19 December 2006
Navigate to the top level to view all replies to the article PC Bootstrap Loader Programming Tutorial in ASM
other nerds have left 2 comments below

also i am going through your code but i got stuck a point. in very start of code we have lines

>mov bx,0×0200
>call readsectors
>but these lines came again after 10 lines. can you help me out whats going on.

ReadSectors is used in the code to perform three different operations (hence why you see it multiple times). The first time is to read the root directory. Under FAT12, the root directory is in the same location ALL the time so it’s possible to look directly at it. This is to determine where the starting point of the file we intend to load is. The second time ReadSectors is called is to read the FAT (file allocation table) and use that index to determine where physically on the disk the file is located. The third (and subsequent) time(s) ReadSectors is called is during the disk reading loop, where the code will read every sector that file resides on and load the image into memory for execution.

I still haven’t had a chance to work on a FAT32 update. Although I did dig out my old FAT32 documents over the weekend.

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RE: Assistance with Code by Anonymous :: NR0

SHOIEB ARSHAD says:
hmm thanks i understand the code completly. now i tries to load COMMAND.com (as i dont have LOADER.BIN ) but it is 93KB long. but from my under standing your code just goes to 31KB or(59 Sectors). what change u suggest to do this.

Posted 20 December 2006, Hide, Parent, Reply

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