Windows Explored

Sometimes you want to make sense of memory usage to gauge its impact on system performance or to just get a better understanding how memory is being allocated. For that, we can turn to the Performance tab in the Windows Task Manager. Here is a quick rundown of the memory metrics the Windows XP Task Manager.

• PF Usage & Page File Usage History
  
  This is not as obvious as it sounds. Before trying to break this down you should know the page file is a temporary memory cache that resides on the physical disk¹. The part of the physical disk that contains a portion of cached memory is a file called pagefile.sys in the root drive. Without getting too technical, we’ll just say information is swapped in and out of physical memory to and from this file to allow programs enough virtual memory to run efficiently². In its earlier Windows days it was known as the the swap file.In the example above, the page file is larger than its usage, i.e 151 MBs of the page file out of 768MBs has been marked as committed, which is not necessarily used. Confused? PF Usage is actually the potential usage, not actual usage. It is considered the size of the page file if all committed virtual memory had to be paged out. Because of this, even if the page file is disabled³, you are always going to see PF Usage.
• Charge
  
  • Total: This is the same as PF Usage in Kilobytes.
  • Limit: Generally, the sum of the current page file (not page file usage), plus the size of physical RAM, e.g. 512 MBs RAM + 768 MB page file.
  • Peak: The highest amount of PF usage since the OS was started.
• Physical Memory
  
  • Total – The total amount of installed RAM (the example here is from a virtual XP system that has been defined with 512 MBs).
  • Available: Generally, the amount of physical RAM that remains after subtracting the “working set”. It is actually comprised of three internal memory lists (see here). This number can never become 0.
  • System Cache: The amount of RAM dedicated to the “working set” or System Process.
• Kernel Memory
  
  • Total: The sum of Paged and Nonpaged memory.
  • Paged: Kernel memory that can be written to the page file.
  • NonPaged: Kernel data structures that cannot be paged and always remain in physical RAM.

Multiple instances of Internet Explorer were opened until the page file grew to its minimum defined size of 25MBs, which kicked off a virtual memory warning.

I repeated opening IE until it would no longer open any further. At this point, the page file reached its maximum defined size, 50 MBs–(50 x 1024 = 51,200).

I could no longer open any further programs and would run into errors when attempting to. You can see below the PF Usage is maxed.

¹Memory allocated to the page file or disk is said be “paged” while anything in RAM is considered “Non-paged”.

²Programs can reside in both RAM and the page file on disk but see themselves as being allocated contiguous memory even though the data is, in fact, fragmented across virtual memory.

³Disabling the page file is a performance-gain myth. You are better off creating a static page file by setting min and max sizes identical or moving the page file to a different physical disk.