Window 8 : RAM usage (committed memory)

Question

I have a 4 GB RAM memory. In task manager you can see tha Committed memory is 5,6/7,9 GB RAM. Why that if In use memory is just 3,1 GB ? Is Windows using the Page File ?

Solution

According to TechNet's introduction to new taskmgr:

Committed virtual memory is private, nonshareable virtual memory created by processes or the OS or drives that MAY need to be paged out. This always starts out in RAM and may get paged out if necessary. So committed memory can be backed by RAM (and if you have no paging file, it remains in RAM until the VM is deleted such as at process exit).

Source: http://blogs.technet.com/b/askperf/archive/2013/08/09/task-manager-in-windows-server-2012-and-windows-8.aspx

So.. yes, Windows is using page file if present but in general it reserves some space in memory - like mentioned above - just in case. However, this commited memory won't necessary be paged out.

Comments

[Jamie Hanrahan]

I wish to caution that the term "reserved" should not be used in this context. "Reserved memory" in Windows is another type of virtual address space allocation that takes no space in either RAM or the pagefile.

[Jamie Hanrahan]

Of the two "committed" numbers, the first is the amount in use, the second is the limit (which is simply RAM size + current pagefile size). Note that even though the current value is 5.6 GB and you only have 4 GB RAM, that doesn't mean that there's 1.6 GB in the pagefile! Some or most of that may have been allocated (in terms of virtual address space allocation) but never accessed yet. In that case it doesn't take RAM or pagefile space. The first time it's accessed, though, it will be manifested in RAM (as the TechNet article stated). This happens on a page-at-a-time basis.

[mwilczynski]

Yeah, you're right. I'll change that to commited as there's definitely a difference.