i managed to solve my problem of hardware interrupts, once i had realized it was hardware i desided that i should try remove all hardware one by one and as i was doin this i went in to the bois setup an noticed that PCI IDE bus master option was enabled, im not sure what this is but after being disabled my pc runs fine. i can only think it got enabled by accedent as it right beside the enable S.M.A.R.T for hard drives option an i had recently turn that off. I have a asrock k7s8x motherboard. just thought id post this incase it helps anyone.

tsuneo if you see the system idle process at 99% don't worry. This is normal when you are viewing task manager with nothing much happening in the background. It's coz it's 99% idle! Dont know a lot but i know this.

Well 2 years on & no problems at all with that PC & i've realised that all the problems in the past have been caused by me! When i do a format & fresh installation I've always then put the service pack next, then all the drivers. The PC then never runs as it should & no matter how many driver updates i install, it's never the same. The last time i started from scratch was 2 years ago & everything is still brilliant. All i did was immediately after installing windows i then installed each driver one at a time. THEN the current service pack. I was told by someone to throw the drivers disk away as it would be outdated but i'm glad i kept it. The windows updates does all of that for you afterwards. What a nerd i am hey?

I know this thread has been solved, but I have a better fix. And cozzy, you were right, it is something simple. Here's the fix I posted on another board.

Interrupts can have a nasty system-wide effect when hogging CPU and it can be worse than you realize. The problem is likely that your IDE ATA/ATAPI disk is running in PIO mode, which is the slowest, due to some time-outs or errors. To check and see if this is the problem, follow these steps:

1. Go to Device Manager (Right-click My Computer>Properties>Hardware Tab>Device Manager);
2. Expand IDE ATA/ATAPI Controllers and click on Primary IDE Channel;
3. Click Properties button and select the Advanced Settings Tab;
4. If the Transfer Mode is PIO and not DMA, this is your problem;
5. Leave Properties panel open.

The fix is relatively quick and painless. It requires two successive reboots. Just make sure you follow these directions all the way to the end or the problem will come back.

1. Open Registry Editor (Start>Run> “regedit”>OK);
2. Expand HKEY_CURRENT_CONFIG/System/CurrentControlSet/Control/Class/{4D36E96A-E325-11CE-BFC1-08002BE10318};
3. Highlight 0001 and click Edit>New>DWORD Value;
4. Type “ResetErrorCountersOnSuccess” and hit Enter;
5. Click Edit>Modify;
6. Enter “1” into the Value Data and hit OK.

This should fix the problem with Interrupts and make your system run much better.

I'm having a similar problem.
It seems the problem only happens when I'm playing a game or watching a movie.
But then, I'm not sure I'd notice it otherwise.
For me, it happens in the middle, not when they're starting up.
It is something that's only started happening within the last month or so.

I think in this time frame I've installed OpenVPN, have disabled a harddrive that way dying, and made the switch from F-Secure to McAffee anti-virus (and I always keep any "real time protection" disabled. I just use antivirus software the traditional way - scan any new software before I run it).

I did the Process Explorer thing right off and it showed CPU usage at 100% when the stuttering fits happen and the "process" eating up all the CPU is hardware interupts.
I understand hardware interupts at a high level, and I think ACPI and interrupt sharing (and Bus Mastering?) are new-ish things that affect interupts.

What I'd really like to find is some bit of software that'd keep a log of when IRQs are tripped and which ones.
I'll bet they're tripped a LOT, but I'd be willing to go through a very large log file to get a hint as to where the problem's coming from.