4 ms·

Is that really true? I booted FreeDOS (had it installed for a while just for kicks) on my Thinkpad T420 (i5-2540M) and I didn't notice any heatup.

• projektfu 6y ago
  Yes and no. The 8086 had a HLT instruction that was meant to replace the busy loop waiting for an interrupt. It was soon understood that you could also save power by turning off the clock. I'm not sure if the "SL" versions of the 486 turned off the clock with the HLT instruction, but later versions did. Use of it was apparently introduced in MS-DOS 6.0, so FreeDOS, Windows 95 and OS/2 2.1(?) would have probably used the instruction to effectively idle the processor. Not sure if Windows 3.1 made use of it, but it would make sense as the basis of the system's event loop. https://en.wikipedia.org/wiki/HLT_(x86_instruction) https://en.wikipedia.org/wiki/HLT_(x86_instruction)
  • lokedhs 6y ago
    I recently installed DOS 6.22 (and Windows 3.11) in a VM and it causes one core to sit at 100% all the time. I don't know if the VM changes anything, but it definitely seems as though it does not halt while waiting for activity.
  • hakfoo 6y ago
    I can recall there were programs like "Waterfall" and "Rain" which were supposed to force Win9x to HLT when idle.