What the heck, this is new.

Well they are actually very old 😉

They're still useful, because Windows 9x virtual machines needs 100% CPU (or core) execution time. Installing one of those in a VM puts CPU time at a reasonable level. Also, they're useless when running under Windows 2000 or XP (because the OS does halt the processor). I don't remember if they offer any benefit with Windows Me or NT4.0.

I remember that those programs (rain, wincooler) worked with almost any CPU (because they only enabled some halt instructions), are your programs K6-2 only? Also, they had problems with some chipsets (but I don't know what chipsets were affected).

they are probably any cpu

Dunno why you call them K62 software coolers when it's not really cpu specific. There's a Rain/Waterfall fan site out there.

I still use Rain and I continue to use it for 14 years. 😀

How does this software work? It optimizes the CPU performance?

There is an instruction (halt) that "halts" (what a surprise) the CPU until an interruption is received. Interruptions are generated by hardware devices (COM ports, the hardware clock, HDD controller), so the computer never locks in that state.

When a CPU is halted it does nothing. In modern CPUs that means that CPU generates less heat. Windows 9x has a "bug" (really is a "feature") related with halt instruction. By design, Windows 9x does not execute a halt instruction (in other systems, like Windows 2000 and later, a halt instruction is generated when CPU is "idle") because Microsoft thought that some chipsets could lock if CPU is halted. That "feature" means that CPU is always working and more energy is wasted and more heat is generated.

Rain, wincooler, waterfall and those programs execute the "halt" instruction when they think the CPU is "idle", so CPU runs cooler (and, as a side effect, a Windows 9x Virtual Machine won't take 100% CPU time).

Personally, I've always been of the opinion I want my CPU working. So constant 100% usage for Distributed.net's OGR project has been keeping mine busy for years (and helps save on heating bills in winter).

I had a Sempron/Athlon 3000+ VIA KT400 Chipset system with windows 2000. But Halt and StpGnt were not enabled by default.
When I enabled Halt with coolon, CPU wattage was like 4 times less. Yet harddisk throughput halved!

In comparison, a VIA KT600 Chipset system with windows 2000: it had a BIOS option for Halt/Stpgnt, and did not suffer from that bug.

Other side effects of Halt on certain older or lower quality chipsets can be: VRM switching noises and corrupted soundfont midi output with SB Live!

That explains it quite nicely, thanks 😀
I thought it was much more complex.

Back in the day I used one of these software CPU coolers, can't remember which but it had specific options for my Athlon XP1700+ and it did lower the idle temps quite a bit - but it caused graphical corruption with my SAA7131 TV capture card. For years I never put 2 and 2 together and just assumed that the card had gone bad until I did a clean OS reinstall and I happened to test the capture card before installing the CPU cooling software. I felt really really dumb for trying countless driver combinations and living with the problem for years without ever considering such a likely reason. 😢

Some Athlon CPUs and chipsets have hardware bugs with power management features like sleep states and this is why motherboard BIOSs will come with things like S2K disconnect and CPU idle detection set to disabled or auto (BIOS checks CPU info first) by default. My guess is your CPU is one with problems and you saw the results.

Some CPU-related info
http://forums.anandtech.com/showthread.php?t=684508

But if you can enable these power management features without problems, it dramatically reduces idle power consumption.