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My machine's CPU usage is low (<10%), as judged from Process Explorer and Task Manager, but the CPU, or HDD Light ( the light just below the power button, at the front of CPU, I am not sure whether it is HDD or whatever) is blinking all the time, as if the whole computer is very busy.

When I open a folder, the folder takes quite sometime to come out.

What is happening?

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up vote 4 down vote accepted

The LED on the front of your computer is for the harddrive, not the CPU. There's a strong chance that your files are scattered in bits and pieces on the harddrive plate, which means you need to defrag your computer (if running Windows, go to Start > Programs > Accessories > System Tools > Disk Defragmenter) which might take some time, and try not to use it while it's defragmenting. This should drastically speed up your computer when you're accessing the filesystem (most of the time).

There is also the chance that your computer is running a process in the background that doesn't require much CPU but does require constant access to the filesystem. This could be a regular application, it could be a process that didn't close properly and is stuck trying to do things with the harddrive constantly, or it could frightfully be some kind of spyware if you haven't ran any spyware checks recently.

Try defragmenting your computer first. If it still runs slowly after that, then it must be a bad process. If you have recently restarted your computer (or if you restart it now) and it is still slow, then it is likely spyware and you should run a spyware cleaner to get rid of it right away. Try Ad-Aware, that usually takes care of most things.

Hope this helps!

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I'm guessing you mean the HDD light, I haven't seen a PC with a CPU light in a long long time, is there a lot of HDD activity going on on your machine. This could be something to look at.

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Is there anyway for me to check the Hard disk activity, ( in the sense of knowing what is accessing hard disk and how to stop it)? – Graviton Feb 22 '10 at 13:00
Use Sysinternal’s FileMon (or ProcessMonitor, but FileMon is easier for this purpose). You can view the file system accesses with it to determine what process is using what files. It should help figure out what’s going on. (You can also easily add some filters if there are some file accesses that you expect.) – Synetech Feb 22 '10 at 13:14
You could look at: it wouldn't tell you how to stop something but would give you a clear idea of whats running and might enable you to find out whats causing all the activity. – Joe Taylor Feb 22 '10 at 13:15
synetech inc beat me to it. Filemon is no longer available for download from the Technet site and has been replaced by Process monitor. If you can find Filemon then give it a go too. – Joe Taylor Feb 22 '10 at 13:16
@Ngu In Process Explorer, add the I/O Reads and I/O Writes columns, which will show the HDD use for each process. The I/O Delta columns are also useful for comparing the instantaneous HDD use - and hence tracking down which process is responsible for a particular performance drop. In Windows 7, the Resource Monitor is also useful for tracking down performance issues. – sblair Feb 22 '10 at 13:17

By "CPU Light", do you mean the hardware LED on the computer? This LED indicates hard-drive activity, not CPU activity. So it sounds as though the hard-drive is the bottleneck, rather than the CPU.

If this is the case, defragmenting the drive may help. Adding more memory may also help, to reduce the use of virtual memory. Or, ultimately, a faster hard-drive (or a solid state drive) may be necessary if the performance issue bothers you.

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Time scales are important here. Computers do things fast.

If the light is turning on briefly 10 times a second, it'll look like a lot of activity to you, but those flashes may represent only a few ms of activity each, meaning that the machine is in fact mostly idle.

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Indeed. If it (assuming it is the HDD activity light) was on solid, then I'd say it was busy, but if it's blinking/flickering, that's normal. – Bonus Feb 22 '10 at 16:23

The light, as others point out, is much more likely to indicate drive activity not CPU activity.

If you are running Windows Vista the default Resource Monitor view will show I/O activity as well as overall CPU activity and memory use. To get to this click Resource Monitor on the Performance tab of Task Manager (to get to Task Manager, right-click your task bar). As well as the graph at the top, the Disk section of the summary below will list disk activity (the closer this % figure is to 100, the more time the OS and apps are spending waiting for I/O operations to complete) and overall throughput. If you click the disk summary row it will given an indication of what processes are actively using your drives.

The memory details may be helpful for diagnostics too. The faults/sec and faults/min figures indicate how much disk->RAM activity is happening. Don't let the work "fault" worry you - a hard page fault just means a processes accessed a page that was currently available in RAM for that operation so the OS needed to read it from disk (either from the program's file or swap space) or make a new copy to write to if it is a copy-on-right page. If you are seeing a few page faults per second during normal operation, or even a few tens, this is quite normal. If you are seeing many specially if it stays high for a period of time then you machine is likely to be thrashing your swap space implying that you either need to close some programs or install more RAM (or that you have a program running that has a memory leak, in which case restarting that may clear the condition).

This information is likely to be accessible in the same place on Windows 7. If you are running XP or before you'll need to make your own graphs in perfmon and/or use 3rd party tools, such as some of the very useful sysinternals utilities, to get the same information.

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You may have a rogue process thrashing on the hard disk that you don't know about. Consider using a utility like DiskMon from SysInternals (now owned by Microsoft) to trace which applications are using the hard disk, and what files they are hitting.

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It's probably defragmenting the disk or maintaining its search index, both of which Windows tends to do during idle time. Either process would spend most of its time waiting for the disk, thus the low CPU usage.

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The light is a Hard drive light and when its briefly blinking every so often you may think its doing alot but really the computer isnt really doing much. my light blinks once every 3 seconds so its not doing to much.

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