Timing accuracy of PC programs running under DOS and Windows

The time in which to press a key and the video retrace interval were measured under various conditions of MS-DOS, Windows 3.1, Windows 3.11, Windows 95, and Windows NT 4.0 Workstation. All the measurements were obtained with the same program running on a single Pentium 300 computer. In all, samples of 1,000 timing measurements were obtained in each of 96 different conditions. Standard deviations of the times ranged from about 0.0006 msec under DOS 6.22 to almost 40 msec under Windows 3.11, representing an increase in timing error of up to 6,000,000%. Researchers requiring millisecond timing accuracy are recommended to use DOS only.