with 4gb ram mine is 6.5gb - 8gb - normal formula is 2x the ram in your system 1.5x if you dont have a lot of space
I'm not positive 2 times ram is recomended by microsoft when you have over two gigs of memory in 64, I know it's not on a 32 bit os from ms
I'm not sure on 64 bit though, I never studied the differances, the rule of thumb of 2 or one and a half ram was created by microsoft when they didn't think people would have more then two gigs and when all we were looking at was 32 bit operating systems
in fact if you leave it to system managed in 32 bit and install 4 gigs the pagefile won't default to over two gigs, you would have to set that manually to over two gigs if you saw the pagefile resizing by the os during work
for those that didn't know it, the pagefile stores new information not old, when you launch a program or file whatever data is in ram just gets released back to the original file, the pagefile is just there when there is new information that doesn't exist anywhere on your disc or network
this is user created info that isn't written to a program, and information you might have deleted while it's still resident in memory, also logs, time and access tags which are were not recorded to your disc before they were registered to the pagefile
once in the pagefile it doesn't get deleted till next boot so if data was newly created in memory there will be an image in the pagefile even if there is a later image on the disc
I don't know how big a pagefile needs to be on 64 bit but if you set it to say 2 gigs the os will just expand the file when it needs to
if of course your disc space is abundant go ahead and make it as big as you like