Assembly Language Help (alang.hlp) (Table of Contents; Topic list)
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Int 15h Function 90h
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     Predefined device types are:
 
     00h     Disk (may time-out)
     01h     Floppy disk (may time-out)
     02h     Keyboard (no time-out)
     03h     Pointing device (PS/2, may time-out)
     80h     Network (no time-out)
     FCh     Fixed disk reset (PS/2, may time-out)
     FDh     Floppy disk drive motor start (may time-out)
     FEh     Printer (may time-out)
 
     For network adapters, ES:BX points to a network control block
     (NCB).
 
     A multitasking program manager would be expected to capture Int
     15h Function 90h so that it can dispatch other tasks while I/O is
     in progress. The default BIOS routine for this function simply
     returns with the carry flag clear and AH = 00h.
                                    -♦-