How much memory to allocate to Photoshop?

If you do not have more than 4GB of RAM installed, you should reduce the allocation to something like 50-60%, especially if you are experiencing slow performance in Photoshop, which includes Camera Raw. To allocate RAM, go to Preferences>Memory & Image Cache and specify a percentage in the Memory Usage section of the dialog box.

Note: You will need to restart Photoshop before the revised allocation can have an effect.