TP 600E CPU 400 MHz with FSB 33 MHz

[harald612]

Hello,

my TP 600E with Win 2000 has a CPU Dixon 400 MHz. Normally it runs at 400 MHz with FSB 66 MHz. When I use the battery and switch energy options to "minimum battery" the FSB is 33 MHz and the CPU runs at 200 MHz.

I do not understand this, because a Pentium II has no SpeedStep. And I thought SpeedStep is hardware driven. Can someone explain?

harald612

[pkiff]

I have never personally witnessed this behaviour and so cannot speak with authority about it, but it appears that Windows 2000 contains some kind of CPU throttling that is OS controlled. It is not the same as SpeedStep, although the behaviour can seem similar and can make it appear that some kind of SpeedStep functions are in place when the effects are really being achieved by throttling the Front Side Bus speed.

When people have mentioned it in these forums, most often it seems to throttle the FSB by 50%, whereas SpeedStep controls the maximum speed of the CPU and either sets it hi (maximum) or low (150MHz less than normal maximum speed).

Your post I think is the first one to mention witnessing this effect with a PII instead of a PIII.

To see some other posts about this topic and other possibly related comments, try:
SpeedStep and Windows 2000 on a ThinkPad 600E
600E Error 102 CPU Runs at 50% of speed (System Timer)
CPU speedstep changes when a ac adapter is connected

Phil.

[harald612]

Hello Phil,

I have checked this behaviour on my TP 600E with Celeron 600 MHz. The Celeron CPU has definetely no SpeedStep. Normally it runs at 600 MHz with FSB 100 MHz.

When I switch the energy options in Windows 2000 to "minimum battery", then the FSB is 50 MHz. The CPU runs at 300 MHz. So Windows 2000 can throttle the FSB by 50%. Very interesting!

Harald

[rkawakami]

Ah, more confirmation! This is exactly what my two 600X systems will do when running Windows 2000 SP4. One of them is a 650Mhz Speedstep, the other a 500Mhz. Both will show the FSB throttle down to 51Mhz when the "Max Battery" power setting is enabled. Which is why I now make sure the power option is "Minimum Power Management".

reference thread: http://forum.thinkpads.com/viewtopic.php?t=26839