Hi, Does anyone still have one of those small DOS programs which slows down the DOS system timer from 18.2 Hz to something slower? I need a programmable timer under DOS and I remember software which allowed the reprogramming of the system timer. Details of the I/O port addresses and registers involved would also be useful. Lucien.

There are programs that will reprogram the system timer. I don't have the port addresses at the present but will get them. You can't get the system timer any slower than 18.2 ticks per second because the chip responsible for the the timing is programmed for the slowest speed possible. It is possible to go faster than 18.2 ticks per second though. The timer chip has several ports than can be programed, but the 18.2 ticks per second drives an interrupt that controls the time and disc drive hardware. Some programs even make use of the timer tick interrupt, so if the 18.2 rate is to be changed then all these factors will have to be looked at.

I don't think the programs you are referring to actually slowed down the system timer. They were a TSR program running loops in the background just to take up processor time so the program running in the foreground would run slower. The purpose was to slow down the processor for older games etc., which were timed by the system speed instead of real time. Or maybe not.