Slow Down PC for Retro Games
The original CPUKiller use case. Throttle your CPU to make old DOS and Windows games run at their intended speed on modern hardware. No download required — runs entirely in your browser.
CPU Throttle Control
Quick Presets
How it works
The throttle tool runs a background Web Worker that consumes a set percentage of CPU time, leaving the remainder for your game. Adjust the slider while your game is running to find the sweet spot.
Why do old games run too fast on modern PCs?
Games from the DOS and early Windows era were often designed with a specific CPU speed in mind. Rather than using frame-rate-independent timing, they tied game logic directly to CPU clock cycles. On a 486 or early Pentium, this worked perfectly. On a modern CPU running at 4+ GHz, the same code executes orders of magnitude faster — causing characters to sprint, animations to blur, and physics to break.
The original CPUKiller software solved this by artificially loading the CPU with a busy-wait loop, consuming enough cycles to bring the effective speed down to what the game expected. This browser-based version does the same thing using a JavaScript Web Worker.
For the best retro gaming experience, also consider DOSBox (for DOS games) or PCem (for full PC emulation). The CPUKiller throttle tool is most effective for early Windows 95/98 games that do not run well in emulators.