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In Windows 7 and Windows 2008 R2, there is a new Resource Monitor that is very useful and powerful to monitor the system.

In the Memory section, I see a section called Modified (orange)

The official description is: Memory whose contents must be written to disk before it can be used for another purpose.

But I am still confused. What kinds of memory is Modified? In which case can we say that this number of memory is Modified? Can anyone give me a specific example?

Is the following guess correct?

When a program want to write something into disk, it actually write the content to an IO buffer, which is in the memory. After OS flush this area of memory into disk, the memory is modified or standby?

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  • Is there anything else about what I have stated that you need cleared up? Maybe it's time to mark the question answered?
    – Everett
    Commented Nov 22, 2010 at 9:11
  • Can you please answer my second question? Is IO buffer belong to modified memory or standby memory?
    – performanceuser
    Commented Nov 22, 2010 at 19:15

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Modified memory is memory that was allocated, modified by the application, and then removed from the application's working set. (The removal usually occurs because it hasn't been used for a long time.) Since it's been modified it can't simply be released for other use; its contents have to be written back to its "backing store". The backing store for private committed memory is the pagefile; for mapped memory, it is the file to which the memory was originally mapped.

Pages normally stay on the modified list for only a brief time before they are written to backing store. Then they are moved to the standby list. Standby pages are considered part of "available memory", because they can be reused for some other purpose if necessary.

The usual reason for pages staying on the modified list indefinitely is because the system doesn't have any available pagefile space left. If you increase the size of the pagefile the system will write most of these pages to disk and then move them from the modified list to the standby list.

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  • Thank you for you explain. Can you please answer my second question? Is IO buffer belong to modified memory or standby memory?
    – performanceuser
    Commented Nov 22, 2010 at 19:15
  • As that's a separate question could you please post it as such?
    – Everett
    Commented Sep 9, 2014 at 14:01
  • The IO buffer in your process address space will have been modified by your program before writing to disk (because you have to put whatever you want to write in it) but that doesn't mean it's on the Modified list, which is what you're asking about. Most apps will reuse the same buffer over and over again, so the pages get referenced often, so they are unlikely to be removed from the process working set.
    – Jamie Hanrahan
    Commented Jun 26, 2017 at 15:31
  • ... and they can't go to the standby list unless they've gone through the modified list and been written to disk.
    – Jamie Hanrahan
    Commented Jul 11, 2017 at 1:12

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