My system:
Windows Vista x64
RAM 16GB
Photoshop CS4 64bit and configurated to use 12GB of RAM (preferences)
Photoshop manages up to 4GB RAM only, but it generate a lot more data in swap file (disk scratch) without using the 8GB RAM available.
What happend?
With a given number of images open and the history palette full for each of them, RAM usage will level out as history states drop off the horizon. You'll reach a threshold level, and you will have to keep pouring in images (or increase their size) to go higher.
Second - if CS4 x64 behaves like CS3, then it always writes to scratch from the moment you open the file. With enough RAM this is purely a background activity that won't slow you down, but you'll notice the disk activity and there will be plenty of stuff in the scratch file. But it does not necessarily mean that RAM is up to saturation.
Another thing I noticed with CS3 is that RAM would hardly ever saturate fully at all, except in very short bursts. Then it would immediately back down, disks spinning. I took this as very effective memory management, and it was reassuring to always have some spare RAM in case of a hungry filter.
Try "Reliability and Performance Monitor" to keep tabs on RAM usage in real-time.
I have 16gb and CS4 will only use all the ram when I am using mega massive files.
Try pushing up the image size /complexity so that they are around 6gb (saved file size) and see what happens....
That's not the point. The point is that Photshop generates a temp file even with very small pics, having (a lot) enough RAM available for the job.
Robert
If you are not having any performance issues I wouldn't lose sleep over it.
Mylenium