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In the Resource Monitor of Windows 7, what does the "disk queue length" really mean?

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In addition, what does the green area and blue lines stand for, as well as the response time of a program (in ms)? And why do some programs have higher response times than others?

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up vote 17 down vote accepted

Disk queue length usually means the length (in number of I/O operations) of the queue of pending operations for a given disk. In other words, how many requests have stacked up waiting for the disk drive to be able to service them. As an example, if I can only process one request a second, but I get 6 requests in a given second, then my queue length will initially be 5 (one request is processed immediately, the five remaining must be queued).

For the meanings of the lines by color, look to the left section at the grey bar towards the middle of the top of the screen. It indicates the color and instantaneous value for each of the variables being graphed.

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I see - thanks for the answer! What does the highest % active time (in blue) mean? – InquilineKea Sep 5 '11 at 6:05
The maximum value of active time as a percentage of total time. – surfasb Sep 5 '11 at 7:01
In other words, if you have multiple disks, it is the maximum active time across all disks – Mark Sowul Nov 25 '12 at 22:15
Conjecture, not really an answer, but since disk queue length (for me, working with a failing HD right now) will only show these discrete values: [0.1, 0.5, 1, 5, 10, 50]. I think this might not be showing actual waiting i/o requests, but the size of the allocated queue. So, when it says '10' it means 'I have allocated 10 spaces in the queue and I'm using some of them'. Showing 0.1 and 0.5 confuses me, because I would expect a queue length to be an int. – FlipMcF Jul 13 '13 at 15:22

This article seems to indicate "Disk Queue Length" refers to the # of processes waiting on the disk. My comment on Slartibartfast's answer is probably wrong.

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