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Windows 7: High CPU usage after waking up - iastor.sys issue

11 Oct 2011   #1

Windows 7 Professional 64 bit
High CPU usage after waking up - iastor.sys issue

I'm running Windows 7 x64 on my ASUS laptop
It works very well , until I have it Sleep . A few minutes after waking up , I realize that the CPU usage reaches 9x-100% , caused by SYSTEM process (2x-30%) , which makes me almost unable to work on it .
I used Process Explorer to explore the process and found out the iastor.sys (resides in C:/Windows/System32/Drivers) that causes the trouble . It consumes >20% CPU while others 0.0x %
Unfortunately I can't take a screenshot , but I believe that's clear enough
I'm thinking of downloading another iastor.sys file and replacing my current one , but I'm not sure it can solve .
Can anyone help me with this issue ? Thanks a lot .

My System SpecsSystem Spec

11 Oct 2011   #2

Windows 7 Professional 64 bit

Here is the screenshot when the laptop works normally .

The one with TID 208 or 212 raises to >20% after waking up and causes the trouble . I can't understand why it only happens after waking up from Sleep (not Hibernate) .
The iastor.sys file doesn't exist in some other computers that I've accessed . Perhaps it went in while I was installing something ... I wonder if I'll get trouble when I delete that file ...
My System SpecsSystem Spec
11 Oct 2011   #3

Windows 7 Professional 64 bit

My System SpecsSystem Spec

11 Oct 2011   #4
Microsoft MVP


That process couldn't run up if you had only the Intel storage driver installed and not the software package which accompanies it. If there is something compelling you to have the software (SMART monitoring or the like) then I would adjust the settings within its controls to try to tame the CPU usage.

Personally I always clean reinstall a factory OEM Windows 7 to get peak performance: Reinstalling Windows 7. You would then only have the driver issued by the Windows 7 installer without the bloatware.
My System SpecsSystem Spec
14 Oct 2011   #5

Windows 7 Professional 64 bit

Thank you .
I installed the latest drivers found on ASUS websites , and that was the reason why I got trouble . Roll back the driver (follow exacly the comment in the link above) is a way to solve that problem .
It's OK now
My System SpecsSystem Spec
14 Oct 2011   #6
Microsoft MVP

Windows 7 Ultimate SP1 X64 (Windows 10, 8.1, Linux Mint, Windows XP and others in VM)

msahci is Windows AHCI driver. iaStor is Intel's AHCI driver. Both will work fine. If you want to use iaStor you have to install Intel Rapid Storage Tehnology program (IRST). If you do not use raid but want to use iaStor, install IRST which will give you iaStor, then go to services.msc and find IRST, right click it and select properties, in the center will be a dropdown menu that probably says Automatic(delayed). Click that, select disabled from the drop down menu then click apply. That way the IRST will not run but you can have use of iaStor as an AHCI driver. Or, you can use MSAHCI which works pretty well.
My System SpecsSystem Spec

 High CPU usage after waking up - iastor.sys issue

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