Miscellaneous / Cache
It is a good idea in general to run with Cache Levels set to 1, which basically turns the cache off. This can be changed in Photoshop->Preferences->Memory & Image Cache Preferences.
The problem with the image cache is that it works with 8-bit data when the view is zoomed out past 100%. This can result in color banding as seen in the screen shot below.
With Cache Levels set to 1, all zoomed out images are created from the 16-bit source data, ensuring a high quality view with no banding. Another advantage is that extra memory is freed up, allowing many processes to run faster. There are some disadvantages, however: Auto Levels will no longer work and some things run slower such as interactive adjustments in a Levels dialog.
If Cache Levels is set to 1, the Histogram Pallet must not be open while processing because Adobe Photoshop will try to update the histogram after every small adjustment, such as moving a slider in a Levels dialog. This can slow Adobe Photoshop down to a crawl when editing large images.