INT 13 - DISK - VERIFY DISK SECTOR(S)
AH = 04h
AL = number of sectors to verify (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 (PC,XT,AT with BIOS prior to 11/15/85)
Return: CF set on error
CF clear if successful
AH = status (see AH=01h)
AL = number of sectors verified
Notes:  errors on a floppy may be due to the motor failing to spin up quickly
enough; the write should be retried at least three times, resetting
the disk with AH=00h between attempts
this function does not compare the disk with memory, it merely
checks whether the sector's stored CRC matches the data's actual CRC
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

See also: 1302

1304 - DISK - VERIFY DISK SECTOR(S)