Table 1 - A summary of the time-related functions provided by the 
                  AT BIOS.
        
        INT 15h (System Services)
             Function 83h (Set/Cancel Wait Interval)
                  Subfunction 0 (Set Interval)
                  Subfunction 1 (Cancel Interval)
             Function 86h (Wait)
        
        INT 1Ah (Time-of-Day Service)
             Function 00h (Read System Timer Time Counter)*
             Function 01h (Set System Timer Time Counter)*
             Function 02h (Read Real Time Clock Time)
             Function 03h (Set Real Time Clock Time)
             Function 04h (Read Real Time Clock Date)
             Function 05h (Set Real Time Clock Date)
             Function 06h (Set Real Time Clock Alarm)
             Function 07h (Reset Real Time Clock Alarm)
        
             * Also available on the PC/XT