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From: android@ccwf.cc.utexas.edu (Andy Wilks)
Newsgroups: comp.os.msdos.programmer
Subject: Re: how BIOS addresses disk sectors
Message-ID: <45632@ut-emx.uucp>
Date: 15 Mar 91 03:40:20 GMT
References: <5405@umbc3.UMBC.EDU>
Sender: news@ut-emx.uucp
Reply-To: android@ccwf.cc.utexas.edu (Andy Wilks)
Distribution: usa
Organization: The University of Texas at Austin
Lines: 19

Function 02, Int 13h reads sectors from the fixed disk as follows:
Input:
AH => 02h
AL => number of sectors to read
CH => Cylinder number (the low 8 bits)
CL => Cylinder number ( 2 high bits ) + Sector Number (bits 0-5)
DH => Head Number
DL => Drive Number (80h=disk1, 81h=disk2)
ES:BX => points to buffer

Output:
AH => 00h = No error
AL => number of sectors read
CF => 0=No error, 1=Error

So we can address up to 1024 cylinders of about 27 sectors each (RLL)
* 512 bytes * 64 heads(???) which allows for a lot of storage!!!

-Andy