There certainly were DOS TSRs that would slow down the system on request. One such is WHOA!.COM, which could be controlled with a hotkey. It worked by hooking the timer interrupt and executing a delay loop on every tick.

I remember using it to make Sopwith playable on a faster computer.

There certainly were DOS TSRs that would slow down the system on request. One such is WHOA!.COM, which could be controlled with a hotkey. It worked by hooking the timer interrupt and executing a delay loop on every tick.

I remember using it to cheat at Sopwith.