Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

 ◄Summary►                                   ◄Up► ◄Contents► ◄Index► ◄Back►
────────────────────────────────────────────────────────────────────────────
 
     The rate at which Int 08h occurs can be adjusted by reprogramming
     the timer chip. A program that adjusts the timer tick rate must
     also include an Int 08h handler that passes control to the BIOS
     service routine only 18.2065 times each second. The handler must
     service all other ticks itself.
 
     For example, if a program increases the timer rate by four, its
     handler must pass control to BIOS every fourth timer tick. This
     ensures that various BIOS tasks──such as maintenance of the tick
     accumulator and diskette motor shutoff counter──are carried out at
     the normal rate.
 
     Int 08h is often used by TSR programs, which trap the interrupt
     with a handler to gain periodic control. A TSR should not adjust
     the timer rate as described above, since its handler cannot be
     assured of receiving control before other handlers.
                                    -♦-