luckie
asked on
Loading Boot Sector to buffer
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 1-63 (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 #00234)
AL = number of sectors transferred (only valid if CF set for some
BIOSes)
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
most BIOSes support "multitrack" reads, where the value in AL
exceeds the number of sectors remaining on the track, in which
case any additional sectors are read beginning at sector 1 on
the following head in the same cylinder; the MSDOS CONFIG.SYS command
MULTITRACK (or the Novell DOS DEBLOCK=) can be used to force DOS to
split disk accesses which would wrap across a track boundary into two
separate calls
the IBM AT BIOS and many other BIOSes use only the low four bits of
DH (head number) since the WD-1003 controller which is the standard
AT controller (and the controller that IDE emulates) only supports
16 heads
AWARD AT BIOS and AMI 386sx BIOS have been extended to handle more
than 1024 cylinders by placing bits 10 and 11 of the cylinder number
into bits 6 and 7 of DH
under Windows95, a volume must be locked (see INT 21/AX=440Dh/CX=084Bh)
in order to perform direct accesses such as INT 13h reads and writes
all versions of MS-DOS (including v7 [Win95]) have a bug which prevents
booting on hard disks with 256 heads, so many modern BIOSes provide
mappings with at most 255 heads
SeeAlso: AH=03h,AH=0Ah,AH=06h"V10DI
SeeAlso: INT 21/AX=440Dh/CX=084Bh,INT 4D/AH=02h
According to the above, how do you setup the registers for loading boot sector (of Hardisk C:) to memory (GAS or GCC)?
Regards,
Jacky
AH = 02h
AL = number of sectors to read (must be nonzero)
CH = low eight bits of cylinder number
CL = sector number 1-63 (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 #00234)
AL = number of sectors transferred (only valid if CF set for some
BIOSes)
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
most BIOSes support "multitrack" reads, where the value in AL
exceeds the number of sectors remaining on the track, in which
case any additional sectors are read beginning at sector 1 on
the following head in the same cylinder; the MSDOS CONFIG.SYS command
MULTITRACK (or the Novell DOS DEBLOCK=) can be used to force DOS to
split disk accesses which would wrap across a track boundary into two
separate calls
the IBM AT BIOS and many other BIOSes use only the low four bits of
DH (head number) since the WD-1003 controller which is the standard
AT controller (and the controller that IDE emulates) only supports
16 heads
AWARD AT BIOS and AMI 386sx BIOS have been extended to handle more
than 1024 cylinders by placing bits 10 and 11 of the cylinder number
into bits 6 and 7 of DH
under Windows95, a volume must be locked (see INT 21/AX=440Dh/CX=084Bh)
in order to perform direct accesses such as INT 13h reads and writes
all versions of MS-DOS (including v7 [Win95]) have a bug which prevents
booting on hard disks with 256 heads, so many modern BIOSes provide
mappings with at most 255 heads
SeeAlso: AH=03h,AH=0Ah,AH=06h"V10DI
SeeAlso: INT 21/AX=440Dh/CX=084Bh,INT 4D/AH=02h
According to the above, how do you setup the registers for loading boot sector (of Hardisk C:) to memory (GAS or GCC)?
Regards,
Jacky
ASKER CERTIFIED SOLUTION
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If you want to read MBR then Dan is absolutely right:
DH should be 0. But if you want to read boot sector of first partition you need to set DH to 1.
DH should be 0. But if you want to read boot sector of first partition you need to set DH to 1.
ASKER
Ok. That will do... Thanks
-- Dan