Click above to get retro games delivered to your door ever month!

  Service 15H (decimal 21) returns information about the type of disk drive
  installed in a PC/AT or PS/2. Given the drive ID in register DL, it
  returns in register AH one of four disk-type indicators. If AH = 00H, no
  drive is present for the specified drive ID; if AH = 01H, a diskette drive
  that cannot sense when the disk has been changed (typical of many PC and
  PC/XT disk drives) is installed; if AH = 02H, a diskette drive that can
  sense a change of disks (drives like the AT's high-capacity diskette
  drives) is installed; finally, if AH = 03H, a fixed-disk drive is
  installed. When the drive type is 3, the register pair CX:DX contains a
  4-byte integer that gives the total number of disk sectors on the drive.