On PCs, PC/XTs, and PC/ATs with ROM BIOS dated earlier than 11/15/85, ES:BX should point to a valid buffer.Verifies the address fields of one or more sectors. No data is transferred to or from memory by this operation.
Call with:
AH = 04H
AL = number of sectors
CH = cylinder
CL = sector
DH = head
DL = drive
00H—7FH floppy disk
80H—FFH fixed disk
ES:BX = segment:offset of buffer (see Notes)
Returns:
If function successful
Carry flag = clear
AH = 00H
AL = number of sectors verified
If function unsuccessful
Carry flag = set
AH = status (see Int 13H Function 01H)
Notes:
On PCs, PC/XTs, and PC/ATs with ROM BIOS dated earlier than 11/15/85, ES:BX should point to a valid buffer.
On fixed disks, the upper 2 bits of the 10-bit cylinder number are placed in the upper 2 bits of register CL.
This function can be used to test whether a readable media is in a floppy disk drive. An error may result from the drive motor being off at the time of the request, because the ROM BIOS does not automatically wait for the drive to come up to speed before attempting the verify operation. The requesting program should reset the floppy disk system (Int 13H Function 00H) and retry the operation three times before assuming that a readable floppy disk is not present.