System idle processes constantly using 80-100% CPU

[Mayet]

Install another hard drive.

If you are constantly running low on space on c drive then you will have no virtual memory.

It also can damage the registry and give various errors. So clean out c drive and leave enough space..like in your case min10 gigs at all times.

[gemstone]

Although 10 out of 240 is barely 'leaving space', consider that on any drive you need enough space to defrag efficiently otherwise your page and MFT files will be in bits which is an ideal performance killer. Depending on the size and type of files on the drive anything up to 50% of free space is needed to properly defrag. I would agree therefore you do need another drive about 300Gb and keep both drives properly defragged.
Also the SIP as explained is correct mine is usually at 99% (now) and if you open task manager and look down the list of CPU % in use by everything it will add up to 99-100% the SIP maintains the balance so.............I knew I'd get there eventually yours means that if your supposedly idle at the time it's showing say 85% then it's too low and other processes are using CPU cycles and those probably are undesirables, so whilst the answers seem to contadict each other and one was corrected, they are agtually both correct originally, intended or not.

So routine maintenance and more drive space.

[Gabriel]

Install another hard drive.

Agreed - but IMHO u can easily free ~50Gb of drive space by removing "uneeded" temp.
You can remove System restore (or adjust it to lower precentage) the Default setting is 12% of total drive size - which means you are wasing 26GB of your drive space on this (Frankly I have never used system restore).
Internet Explorer 10% of the total drive size - another 24GB.

Also - check under Windows Folder - you can remove all the "blueish" Windows update folder ($NtUninstallKBxxxxxx$) - I do it on a regular basis.


Cheers,
Gabriel

[geoscomp]

Microsoft says for a complete defrag you need at least 15% free space..for your 240 gb drive, that would be 36gb. Without that space to rearrange files in, windows will only partially defrag the drive. The answers about the system idle are also correct..system idle is just that..the percent of the cpu process ability that is idle..not doing anything. The totals HAVE to add up to 100% of the processor capability. (btw..that 15% Microsoft recommends is just a starting point, and it does NOT include virtual memory space..you need at least 15% above the space for everything on the drive INCLUDING virtual memory.

[DonJ]

I believe the basic rule-of-thumb is to have a minimum of 20% free space. It just makes sense. That is what HP recommends on their servers.

As stated above, you need it for Virtual Memory and spool files. HP calls it Transient Disk Space.

[arch0nmyc0n]

Whilst I know you'll probably dismiss this answerto your problem , I figure I'd suggest it anyways. Why not have your computer reboot itself very eraly in the morning or whenever you're sleeping? I was having similar issues with one of my systems and I simply set it to shut down at 4:30am and start back up at 4:45am... It helped alleviate most of the slowdown and memory problems with the machine. Though I wasn't running with that amount of free space... as everyone is suggesting you should really keep more space available. I always try to leave 20% of my drive available at all times...