Photoshop uses a scratch disk (temporary disk space used for storing data and performing computations) when there is insufficient RAM for image editing.

Taken from the Adobe site, now we have a definition. So these swap files are created when you’re working on large images, but what happens when Photoshop crashes? Well Photoshop doesn’t have the sense to clean up your scratch disk and delete it’s temporary files. So this is a warning to everyone…

When Photoshop crashes (which I find is quite often when working with large files -.-) be sure to manually clear out the temporary files created in the previous session, otherwise they will just sit there clogging up your disk space, making Photoshop run even slower and become even more unstable!

As you can see from the image above, one scratch file here was nearly 7Gb! If you get a couple of these building up you’ll really start to notice. So have I got you worried? Here’s the default location of Photoshop’s (correct for CS3/4) scratch disk (you will probably need to make hidden files visible to get here):

Vista: C:\Users\Whoever\AppData\Local\Temp
XP: C:\Documents and Settings\Whoever\Application Data\ (I’m gussing)
Mac/Linux: You’re on your own :]

The file names you’re looking for will be quite self explanatory. Provided the application is not running, I have never had any problems or data loss from deleting these files, but do esercise some caution!

Good luck

p.s. I assume this applies to all members of the Creative Suite after a system crash, so keep your eyes peeled for temps littered about the place.