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"V10DISK.SYS",AH=21h"PS/1",AH=42h"IBM"
SeeAlso: INT 21/AX=440Dh/CX=084Bh,INT 4D/AH=02h



INT 13 - DISK - GET DISK TYPE (XT 1/10/86 or later,XT286,AT,PS)
        AH = 15h
        DL = drive number (bit 7 set for hard disk)
Return: CF clear if successful
            AH = type code
                00h no such drive
                01h floppy without change-line support
                02h floppy (or other removable drive) with change-line support
                03h hard disk
                    CX:DX = number of 512-byte sectors
        CF set on error
            AH = status (see #00234 at AH=01h)
Note:   SyQuest can report type 01h or 02h for 'hard disks', since its media
          is removable
BUGS:   many versions of the Award 486 BIOS do not return the sector count
          because the BIOS exit code restores CX and DX to their original
          values after the function had already set them to correct values
        several different Compaq BIOSes incorrectly report high-numbered
          drives (such as 90h, B0h, D0h, and F0h) as present, giving them the
          same geometry as drive 80h; as a workaround, scan through disk
          numbers, stopping as soon as the number of valid drives encountered
          equals the value in 0040h:0075h
SeeAlso: AH=08h,AH=16h,AH=17h,AH=19h"SCSI",MEM 0040h:0075h
