axis said:
Why do I still need a page file, even when I have 1 Gig of ram and my RAM
usage normally hovers around 3-400mb? If I set the page file to be very
small windows XP goes nuts. I understand the need for page files in memory
constrained situations, I would appreaciate some info as to why one needs it
even in a situation where we shouldn't need to page any data our of memory
to disk.
thanks
One big reason is that Windows uses the page file to satisfy the
memory address space requirements for the unused portions of memory
allocation requests.
By design Windows must identify specific memory address space for all
of the memory allocation requests that are issued, whether by Windows
itself, device drivers, or application programs. And all of these
typically ask for allocations that are larger that what is usually
needed under normal circumstances. So what Windows does is to
allocate RAM only to those portions of these requests that are
actually used and uses space in the page file for the unused portions.
Two points about this:
1. Mapping of these unused portions of memory requests to the page
file does not require any actual writing to the hard drive. All that
is need is entries in the memory mapping tables maintained by the CPU.
2. Windows Task Manager includes the swap file space allocated to
these unused ports as Page File Usage in the data reported on the
performance tab.
And if subsequent events result in the usage of previously requested
but unused memory then it can be instantaneously remapped from the
page file to an available location in RAM.
The bottom line, insofar as the current topic is concerned, is that
the existence of the page file will make the actual usage of your RAM
more efficient. Without a page file it is quite possible, indeed even
likely, that you would have a couple of hundred megabytes of RAM tied
up for memory that was requested but never used.
Also you need to be aware that Windows does use the page file for more
than just swapping out of memory content from RAM. It is also used
for:
a: System Failure Memory Dumps, unless you have this option
configured as "no memory dump". And in order for this option to be
usable there must be an existing page file on the boot drive that is
at least as large as the dump size option selected.
b: If you have multiple users configured on the computer and if you
have the "fast user switching" option in effect then Windows will use
the page file to "roll out" the memory contents of the previous user
when the machine is switched to a new user.
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."
