It's a ThinkPad W510, with Windows 7.
I've been struggling with this since I got the laptop. Very often, say for 20-30 minutes at a time several times a day, the laptop gets painfully slow. I'm usually working in Visual Studio, but the slowness isn't isolated to that. Chrome is slow, even opening the start menu is slow. So slow, I can type a sentence in notepad and it won't show up until 5 seconds later.
The HDD light is flickering during this time, usually. I have tried to figure out what process or service might be using the CPU, but even at its worst, there's only about 20% usage from other processes (spread across a few that don't surprise me). One suspect process is svchost.exe which sometimes gets up to 15% usage, but when I use Resource Monitor to see which services are to blame, none really pop up as a culprit -- none go higher than say 6% for very long. Still, I've shut down a lot of services in an attempt to figure it out. But it hasn't had any effect. Since the CPU doesn't climb to 80% or anything, it seems the problem isn't CPU usage, but some other bottleneck (hdd? some kind of lock? handles?)
What's really interesting is that while the slowness is occurring, if I unplug the laptop from the AC power, it goes away almost instantly! Apparently, whatever is causing the problem is setup only to run while on AC power.
I guess what I'm looking for from here is ideas on how to better identify the problem. My dabbling in resource monitor and sysinternals process monitor is not really helping. What should I be looking out for?
My problem turned out at least partially to be due to 'CPU Parking'. Windows 7 has a feature where it can 'park' CPUs to save energy. I've disabled it via a reg hack and I haven't had the problem since. I still have slightly higher CPU usage while plugged and I haven't figured out why since no one process seems to be to blame, but now it doesn't slow the computer down.
Turned out I still had problems even with CPU parking disabled. The real problem turned out to be that I was using a 90W power supply, and the thinkpad's power management mistakenly thinks this is not enough power and slows the CPUs down to save power. Using the 135W power supply fixes it. Some people have other suggestions, even a hardware hack: