INT 13h,  10h (16)       Test for Drive Ready                      fixed disk

    Tests to see if the fixed disk drive is ready. This service can be
    performed on fixed disks only.

       On entry:      AH         10h
                      DL         Drive number (Bit 7 must be set)

       Returns:       AH         Status of operation (See Service 01h)
                      CF         Set if error, else cleared

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       Notes:         If the fixed disk drive is ready, then AH is 0 and
                      the Carry Flag is clear.

                      For the AT, XT-286, and PC Convertible, the BIOS
                      executes INT 15h, Service 90h (Device Busy), for the
                      diskette (Type = 01h) and the fixed disk (Type =
                      00h) prior to waiting for the interrupt. INT 15h,
                      Service 91h (Interrupt Complete), is executed upon
                      completion.