Int 1A Fn 00  - Time - Get System Time                                     [B]

   AH = 00h

Return: CX:DX = number of clock ticks since midnight
   AL = midnight flag, nonzero if midnight passed since time last read

Notes: there are approximately 18.2 clock ticks per second, 1800B0h per 24 hrs
   IBM and many clone BIOSes set the flag for AL rather than incrementing
     it, leading to loss of a day if two consecutive midnights pass
     without a request for the time (e.g. if the system is on but idle)

See Also: AH=01h,AH=02h,INT 21/AH=2Ch,INT 62/AX=0099h