Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!pasteur!ucbvax!hplabs!hp-pcd!hpcvlx!bill
From: bill@hpcvlx.HP.COM (Bill Frolik)
Newsgroups: comp.sys.ibm.pc
Subject: Re: What is the fastest disk access method on AT?
Message-ID: <101000015@hpcvlx.HP.COM>
Date: 26 Oct 88 14:52:45 GMT
References: <211@focsys.UUCP>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 80


The simplest thing to do is replace your Int 25h and Int 26h calls with
calls to BIOS Int 13h functions 2 and 3, which is basically what DOS
does with your 25h/26h requests after adding a layer of buffering and
converting your absolute sector request into an equivalent cylinder, head,
and sector number.  So you don't have to look it up in your tech ref
manual, the following four Int 13h functions are probably all you need.
Remember that the first hard disk in your system is drive number 80h, and
that sector numbers start at 1, not 0.  Also, be sure to check error status
after each function; as long as AH keeps coming back zero, you're okay.

	RESET DISK	Resets the controller and recalibrate to track 0.

		Specify:	AH = 0
				DL = Drive unit number
	
		Returns:	AH = Error status
			
	GET PARAMETERS	Get information about the drive specified in DL.

		Specify:	AH = 8
				DL = Drive unit number
	
		Returns:	AH = Error status
				CH = Max cylinder number
				CL = Sectors per track
				DH = Max head number
			     ES:DI = Pointer to disk parameter table
				     (I don't have the table in front of me,
				     but I think it contains somewhere the
				     number of bytes per sector in addition
				     to all this other information.  Normal
				     DOS disk sectors are 512 bytes long, but
				     sometimes folks use larger values on 
				     hard disks to "break" the 32M limit.)

	READ SECTOR(S)	Read one or more sectors from the disk.

		Specify:	AH = 2
				AL = Number of sectors to read
				CH = Cylinder number (0-n)
				CL = Sector number (1-n)
				DH = Head number (0-n)
				DL = Drive unit number
			     ES:BX = Address of data buffer
	
		Returns:	AH = Error status
				AL = Number of sectors actually read
			
	WRITE SECTOR(S)	Write one or more sectors to the disk.

		Specify:	AH = 3
				AL = Number of sectors to write
				CH = Cylinder number (0-n)
				CL = Sector number (1-n)
				DH = Head number (0-n)
				DL = Drive unit number
			     ES:BX = Address of data buffer
	
		Returns:	AH = Error status
				AL = Number of sectors actually written
			
	Error codes:	00 - No error
			01 - Bad command or drive number
			02 - Address mark not found
			03 - Write protect violation
			04 - Sector not found
			05 - Reset failed
			06 - Disk change error (floppies only)
			08 - DMA overrun on last operation
			09 - DMA overrun
			0C - Track/sector combination not supported
			10 - Bad CRC on floppy read
			20 - Controller failure
			40 - Seek failure
			80 - Timeout

-----------------------------------
Bill Frolik / hp-pcd!bill
Hewlett-Packard / Corvallis, Oregon