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Old January 20, 2009, 06:23 PM
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Chilly Chilly is offline
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Exclamation Whats up with my CPU? - A SpeedStep F.A.Q.

So you've just set up your new PC, your playing around with it, salivating at all the technical details, when you happen to open CPU-Z or some similar program. Maybe you've overclocked it, maybe you haven't but either way you quickly realize that something seems, off. With in seconds you clue in that your CPU seems to be running slower than it should, underclocking itself and running at half the speed you paid for.

This CPU is a Q6600 overclocked to run at 3.4GHz, so wheres my missing 1.2GHz?!?!!!!1


So whats up? What wrong with your CPU? Nothing actually, its working exactly as intended. Its a little known feature called SpeedStep, which will down clock your voltages and multiplier whenever your computer is idle(low load) or not in use. Its actually quite an innovative feature, that saves electrical power, lowers your heat dump, and keeps your hydro bill down.

As usual Wikipedia explains it best;
Quote:
SpeedStep is a trademark for a series of dynamic frequency scaling technologies built into some Intel microprocessors that allow the clock speed of the processor to be dynamically changed by software. This allows the processor to meet the instantaneous performance needs of the operation being performed, while minimizing power draw and heat dissipation.
So what happens to that power when its needed? Well, the instant its needed, its given to you faster than you can blink your eyes. SpeedStep will ramp up, turn up the voltage and multiplier, and set you sailing full speed ahead!

There's my missing 1.2GHz! Go Go Rosetta @ Home!


Leave it On or Off?
So the next question usually is, how does this affect me, should I leave it on, or off? Well that depends, if your simply leaving your CPU at stock, I highly recommend you leave it alone, turning SpeedStep off will do nothing for you except higher hydro bills. In fact, even if your using an overclocked CPU, I would recommend to leave SpeedStep on, rarely, if ever, does SpeedStep cause stability issues, if your overclock is stable in the first place, then SpeedStep should not destabilize it.

On the other hand, if your in the process of overclocking, doing suiciding runs, or etc, and have not yet found a stable 24/7 overclock, then SpeedStep can cause issues. SpeedStep can make an unstable overclock seem stable, and a stable overclock seem unstable due to its constant shifting of voltage and multiplier settings.

Performance
Now onto the question still on everyone's minds, how does it affect performance?

Short answer; it doesn't, your computer will perform just as fast with it on as it does off. It ramps up the speed so quickly that any performance intensive program(Gaming, Rendering, Folding, Crunching, etc) will not even know that your CPU was running at half its speed only moments ago.

Longer answer; sometimes it can be, for example in a few synthetic benchmarks such as SuperPi in which milliseconds matter, the slight(VERY SLIGHT) time in which it(SpeedStep) takes to ramp up can affect the resulting, resulting in a slower posted time. Real world applications, and even most benchmarks, simply aren't affected by the time(minuscule as it is) that it take to ramp up, but it is worth mentioning as there are a few (rare) cases such as SuperPi where SpeedStep can adversely affect the performance.

Other Points to Consider
One last thing that must be brought up and that is, C1E. C1E is a feature that works as a part of SpeedStep, but it is NOT SpeedStep, nor technically part of it. If you are running an overclocked CPU, no matter how stable, I would HIGHLY recommend turning it off in BIOS. The reason for this is simple, C1E likes to play with your Voltage settings, ALOT.

As plenty of us know, at times its an art finding voltage settings that an overclocked CPU likes and is stable at. The issue with C1E is that it will drop your voltage down, and unlike SpeedStep which is almost instantaneous, C1E takes a few extra milliseconds to kick in. While not an usually an issue when a CPU is at stock clocks and voltages, it can be devastating to the stability of an overclocked CPU, as they are more sensitive to voltage changes.

How do I turn it off?
If you still feel the need to disable SpeedStep, read on for a step by step guide on how to disable it in BIOS(hardware) and/or Windows(software).

Last edited by Chilly; August 13, 2009 at 01:34 AM.
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