🚀 go-pugleaf

In article <exuptr.458.716059101@exu.ericsson.se> exuptr@exu.ericsson.se (exuptr@exu.ericsson.se) writes:
>In article <2aab4eed@ralf> Ralf.Brown@B.GP.CS.CMU.EDU writes:
>>are 1024 cyl x 64 heads x 63 sectors/track--a little less than 4G sectors
>Now this one makes sense.  Except that BIOS does not limit you to 1024
>cylinders, that is DOS.  So theoretically you could have 2048 x 64 x 63.

No, originally the *BIOS* only had 10 bits for the cylinder address.
Later more modern Bios's allow 12 bits (4096 cylinders) but since that is
non standard, DOS can not make use of this.

From Ralf's interrupt list....
----------1302-------------------------------
INT 13 - DISK - READ SECTOR(S) INTO MEMORY
	AH = 02h
	AL = number of sectors to read (must be nonzero)
	CH = low eight bits of cylinder number
	CL = sector number (bits 0-5)
	     high two bits of cylinder (bits 6-7, hard disk only)
	DH = head number
	DL = drive number (bit 7 set for hard disk)
	ES:BX -> data buffer
Return: CF set on error
	    if AH = 11h (corrected ECC error), AL = burst length
	CF clear if successful
	AH = status (see AH=01h)
	AL = number of sectors transferred
Notes:	errors on a floppy may be due to the motor failing to spin up quickly
	  enough; the read should be retried at least three times, resetting
	  the disk with AH=00h between attempts
	AWARD AT BIOS extended to handle more than 1024 cylinders by placing
	  bits 10 and 11 of the cylinder number into bits 6 and 7 of DH
SeeAlso: AH=03h,AH=0Ah
-- 
                               Stephen Harris
               sweh@spuddy.uucp    ...!uknet!axion!spuddy!sweh

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