Solution:

There are three system times in a computer system ?DOS time, BIOS time and RTC(CMOS) time. For example, under DOS environment, we can access the three system times by using: DOS interrupt 0x21, 0x2A/0x2C BIOS interrupt 0x1A, 0x04/0x02 RTC(CMOS) direct port addressing However, if you check these three system simultaneously, you will find that the DOS time is always different from the BIOS time (slower or faster). As a result, it is better for an application to use the BIOS time instead of using DOS time. Get DOS Date Software interrupt AH = 0x2A CX:Year DH:Month DL:Day AL: 0 - Sunday 1 - Monday 2 - Tuesday 3 - Wednesday 4 - Thursday 5 - Friday 6 - Saturday Set DOS Date Software interrupt AH = 0x2B Success: AL - 0 Fail : AL - FF Get DOS Time Software interrupt AH = 0x2C CH for Hour : 0-23 CL for Minute : 0-59 DH for Second : 0-59 DL for 1/100 second : 0-00 Set DOS Time Software interrupt AH = 0x2D Success: AL=0 Fail: AL=FF For BIOS Time Software Interrupt 0x1A, 0x04/0x02 Get RTC Date (CMOS) To read 128 Bytes CMOS data (for AWARD BIOS), you must use direct port address. Index Port 70 Data Port 71 For Year (09H) C:>DEBUG -o 70 09 -i 71 98 For Centry (32H) C:>DEBUG -o 70 32 -i 71 19 I am sending you a small utility Viewcmos.exe. It can show the three system time at same time. As for the programing and register please refer to the source code time.c and you can run the example file R-time.exe There is an tsr program that can update DOS time continuously.