cpu-idling.md

December 14, 2023 · View on GitHub

Some operating systems don't support hlt instruction, because of this, the CPU spin loops instead of idling. Here are some solutions for different OSes:

MS-DOS (using DOSIdle)

  1. Download DOSID251.zip from https://www.vogons.org/viewtopic.php?p=438763#p438763
  2. Unzip DOSIDLE.EXE from archive in any location (recommended to root of C:).
  3. Run edit C:\autoexec.bat
  4. Add to file: C:\path\to\dosidle.exe
  5. Save changes (press Alt + F and x) and restart the VM.

Note: To hide output when starting DOSIdle, change C:\path\to\dosidle.exe to C:\path\to\dosidle.exe > nul on step №4.

FreeDOS (source)

  1. Run edit C:\fdconfig.sys (or edit C:\config.sys)
  2. Add to file: IDLEHALT=1
  3. Save changes (press Alt + F and x) and restart FreeDOS.

Windows 9x (using AmnHLT)

  1. Download amnhltm.zip from http://toogam.com/software/archive/drivers/cpu/cpuidle/amnhltm.zip (mirror)
  2. Unzip the archive in any location.
  3. Note: If you have installed VBE9x, restart Windows, press F8 on boot, select Command prompt only, run cd C:\path\to\amnhlt\, and follow to the next step.
  4. Run AMNHLT.BAT
  5. Restart Windows, and AmnHLT will start automatically on next boot (you can safely delete archive and unpacked folder).

Windows 98+ and Unix-like

These systems are already supports hlt, no further action is required.