"System Idle Process" Explained

the cpu will hardly ever be under pressure enough to be at 100%

mostly games can do that...chess master comes to mind

most users usually have the processors running aobut 10-20% of the max...of that percentage, the most of the cycles are doing nothing at all,and the system idle process carries those wasted cycles.
Munk, the entire time I was reading the article, I was still clinging to what I had always believed, that being exactly what you stated. I'm going to ellaborate on what I had previously understood, perris, simply so that you can get a better understanding on what we are talking about and correct us if need be.

As far as I have been aware, Task Manager represents the entire 100% of your CPU usage. Therefore, if you are running a game that task manager displays as having a CPU Usage of 100% (quite a common scenario in the gaming world) then the Idle Process will drop right down to 0%. However, if you were making no load (or very little - say about 2%), then the System Idle Process will jump up to 98%.

So as an example, say you are using about 10% of your CPU, what happens to the other 90%? Your processor cannot simply sit there and do "nothing" with that 90%, therefore it runs the "System Idle Process" to make up the remaining CPU cycles. Task Manager will then display the Idle Process as having 90% usage.
Therefore, if you take the 10% you are using (say in explorer and word) and add it to the System Idle Process (being 90%) then you will get exactly 100%.
And this is true for any circumstance. If you add up the usage of each of the processes running on your system and it is below 100, then the System Idle Process will always display the remaining percentage to make up a total of 100%.
This is what Monk was trying to demonstrate with the screenshots.

When you said:
most users usually have the processors running aobut 10-20% of the max...of that percentage, the most of the cycles are doing nothing at all,and the system idle process carries those wasted cycles
I think that seems to match up with what we are saying.
However, I think the confusion has arrisen due to statements such as:
it's not 90% of your CPU that it's taking, it's 90% of what the CPU's load is for instance, go to the performance graph...if the CPU's load is 1%, and system idle is using 90% at that time, then system idle process is using 90% of the one percent. in other words, 9/10th's of one percent in this example
I still don't really understand that example. Firstly, it's a bit misleading because we know that the total amount must add to 100% so it should either be 99% (load) + 1% (system idle process) or 90% + 10%. But apart from that, I never really saw the System Idle Process as being a percentage of the "current" load. A percentage of the "total" load maybe, but not of the current load..? Otherwise it would not explain why the System Idle Process decreases when the load increases (at an exact rate which always seems to add to 100%). It's more like a remainder, the remainder of your total CPU usage, based on the amount you are currently using.
I think the primary difference between the arguments is that you are multiplying the System Idle Process against the load (which produces the weird fraction), while we are instead adding them together (which always produces an exact 100%, seeming to represent the total load)

But it's interesting nonetheless! I'll have to read up a bit more into it another time but unfortunately I have my major end of school exams (which decides which uni I get into) over the next three weeks so I'll have to be studying :( (But at least I have FOUR MONTHS holidays to look forward to after them :D)

Anyways, thanks perris for the great explanation regarding the specific workings of the CPU, it is very informational (and very advanced! lol).

"100% busy" doesn'tt mean all the resources on the chip are in use. It means "was't running the idle thread at any time during task manager's last sampling,

a CPU is actually either idle or busy there's really nothing in between.

Your "% CPU usage" is actually an average of a time frame, for instance, if a CPU has been busy for half a second the last second, that'll look like 50% in the task manager but that counter doesn't tell us how many or how few "resources" on the CPU were actually in use for that 50% usage during that time

at any rate, I've re writwb the last paragraph, as wasn't precise
I'm no English major, but i'm pretty sure your quanta/quatum usage you mentioned in the quote below was correct the first time around. While the sentence on a whole is talking about more than one unit of measure, the word "one" preceeding the unit makes the singular form the correct one to use. Its a comparative statement and you are comparing the number of units to a singular unit.

Great post by the way...!

perris said:

websters dictionary;

Main Entry: 1quan·tum
Pronunciation: 'kwän-t&m
Function: noun
Inflected Form(s): plural quan·ta

so you have it backwards, my paper was correct in that regard.

I did however find one gramma mistake I wouldn't have spotted if not for your post...so thanx for that

I had written;

'...more then one quantum

corrected now to;

...more the one quanta
The total of all percentages listed in the task manager should add up to 100%, because of rounding it may add up to 99% at times.

Think of it this way. The "System Idle Process" is a program (a process really) running on you system, just like any other. The amount of work that your processor can do it represented by 100%. When their are enough processes that need to do work, then all 100% percent of the work your CPU can do can be assigned to them. But what happens when the system is just sitting their, and only enough processes are running to use say 5%? The computer can't simply toss the CPU cycles out the window they must be assigned to some process. So in Windows a process was created, called the "System Idle Process". The purpose of this process is to use CPU cycles that would go unused otherwise. Its something of a garbage disposal for CPU cycles. Its an actual program (a process really) that is running on your system. Its running at the absolute lowest priority possible so that all other processes on your system are give CPU cycles first, and only when no other process is in need are they give to the "System Idle Process"

Hope this helps...instead of further confusing the issue....

munk said:
Does this mean that it is not clear, how much total cpu load is used? Are these 100 percent not the one hundred percent my cpu could work? Is that what I misunderstood?

I'm not saying that you're wrong. I believe you're right. But if the task manager does not show the "real" load of my cpu it would be very useless.
I may be mis-reading this discussion, but is the CPU usage shown on the'performance' tab of task manager the actual load on the processor,andthe percentage shown on the 'processes' tab the percentage of thatload?

If this is the case, then sometimes (well quite often) my CPU usage isat or almost at 100%, with the system idle process taking up allofthat.

I know of other people experiencing this with a range of hardware set-up's and some on Xp, some 2K.

What occurs?

now to answer what I beleive is your question;

all the system idle process represents are cycles that are not being used.
Thanks for the warm welcome (and speedy response!).

How does this tie in with the cpu usage in performance?
if you see that your cpu is 80% as a total, you'll also see the system idle process is 20%

it will always be an inverser of 100%
I've done some crafty capturing and attached them to explain better....

I loaded the old fella with some calculations so that the cpu use is maxed out, and the performance tab looks like this....


And this is how the process tab looks. The top three processes add up to 100%.


I understand what you are saying about how there must always be 100% in total on this section, and in this example it seems obvious what is going on, i.e. ud_ligfit_Relea is using almost all of the processing capability.

However - when I have no programs running - sometimes my system is slow and when I check the performance the cpu is at 100% (in the same way that it is on the first capture), but when I check the processes the only thing is system idle, at 99.

Sorry if I'm being remedial and you've already explained this..



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the system idle process couldn't be at 99% when the cpu is representing 100%

the system idle would be at 0 when the cpu is at 100

what is that first process that's using all that cpu time by the way?
Looks like one of those united devices, cure for cancer type things.
Sure is.... it's a good use of my PC when I'm drinking coffee

Check it out at http://www.chem.ox.ac.uk/curecancer.html

It'd be cool if everyone started doing stuff like this.

.... back to the techy stuff, that's the problem. I've been having thisfor a while where the only process apparently using any resources issystem idle, yet the cpu usage is at a maximum. I'd decided it musthave been something odd on my work machine, but I was talking to afriend at the weekend who was having the problem, and it piqued mycuriosity again, which led me here...

I thought that it didn't make sense, hence the research.
it's excellant, we have a program here at osnn like it for a differant cause

back to your question;

the system idle can't be showing anyhting when the cpu is at 100

show us a screenshot of that if when it happens again.
OR... join the OSNN.net folding team. Folding proteins for medical science.

[edit] oops, perris sorta said that...
Just a tiny Question, my Puter is Hyper-Threading, how does that fit in with the explanation here .

niteghost said:
Just a tiny Question, my Puter is Hyper-Threading, how does that fit in with the explanation here .

That's a bit trickier if you look at the graphs. But the meter on the cpu tab should add upp to 100% - System Idle Service in the processes tab.
okay still confused and have a pic.

cpu usage is 32% but system idle process is 71, where and how does cpu usage fit in. Is wmplayer.exe using 16% of 32%? and why doesn't it add up to 100, 71+16+3+3+3+3=99. they are orded by the cpu column.


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