Donald McDaniel said:
Your understanding is incorrect. As an example, I currently have 512MB of
memory, half of which is usually in use (that means 200+meg is usually
available for use by the OS, but almost NEVER gets used, unless I open MANY
windows). At the same time, XP Pro ALWAYS uses a swapfile of 180+mb. This
may be due to my own misunderstanding of swapfile usage. Or it may just be
due to allowing XP to manage virtual memory, instead of managing it myself.
XP does not manage memory by using all available physical memory, then using
the swapfile when there is no more physical memory available. Instead, it
creates memory pools of "virtual memory" (some of which is swapfile, some of
which is physical memory) and uses that.
Not quite correct.
What happens is that most programs, device drivers and also Windows
components always request more memory than they actually use under
normal circumstances, sometimes very substantially more.
By design Windows must provide memory address locations to satisfy all
of the memory requests that are issued, whether the full requested
amount is used or not. So what happens is that the portion of the
request that is actually used is mapped to addresses in RAM and the
unused portion of the request is mapped to the swap file. Because the
memory is unused this requires no disk activity or anything, just an
entry in the memory mapping tables maintained by the CPU.
And if something later decides to make use of more of the memory it
originally requested then that portion can be instantly remapped to an
available location in RAM.
Windows Task Manager, and many other reporting tools, report the swap
file space mapped to meet the unused portions of these memory requests
as being "in use" which is somewhat correct from a technical point of
view. But nothing has every been written to these swap file locations
and there is no disk activity associated with these items.
However it is also possible that Windows will move some items from RAM
to the swap file so as to allow that RAM to be used for other,
currently more important uses. This is the real 100% genuine "swap
file in use" that Windows XP does not have any convenient method of
identifying or reporting. You can download a free utility written by
MVP Bill James from
http://www.dougknox.com/xp/utils/xp_pagefilemon.htm or from
http://billsway.com/notes_public/WinXP_Tweaks that will report the
actual page file usage of your system, that is memory pages that have
been written out to the swap file and dropped from RAM.
One very useful purpose of this utility is to identify when adding
additional RAM is likely to provide a performance improvement. As a
general rule if this utility reports actual swap file usage of 50 mb
or more on a consistent basis then additional RAM is probably a
worthwhile consideration. But if it does not report 50 mb of actual
usage then there is little likelihood that adding RAM will improve
performance to any noticeable extent.
Using my computer as an example it is currently reporting in Task
Manager that I have Page File usage of 277 mb. However Bill James'
utility indicates that the actual usage at present 41 mb. These
figures taken together tell me that there is a total of 236 mb of
memory that has been requested but never used by the various items
that are currently running on the computer.
Hope this explains the situation.
Good luck
Ron Martell Duncan B.C. Canada
--
Microsoft MVP
On-Line Help Computer Service
http://onlinehelp.bc.ca
"The reason computer chips are so small is computers don't eat much."
