How Photoshop Works

• When you open an image in Adobe Photoshop, it immediately loads the image using your RAM (Random Access Memory) instead of working directly off your hard drive. Loading the image this way allows for faster computation for color adjustments and other image plug-ins.
  
  

RAM Overload

• The function of a scratch disk in Adobe Photoshop is to handle computations, such as complex graphic filters, that exceed the amount of RAM you have in your computer. When the image adjustment s exceeds the amount of available RAM, Photoshop "borrows" additional memory from your hard drive
  
  

Setting Scratch Disks in Photoshop

• By default, your primary scratch disk is the same hard drive the program is installed on. You can change this settings by going to "Preferences" under the "Edit" menu and selecting "Plug-Ins and Scratch Disks..." You can also designate multiple scratch disks from this same menu dialog.
  
  

Primary Scratch Do's

• You should use a local drive, not a network drive, for your scratch disk. Whichever drive(s) you designate as a scratch disk should be defragmented on a regular basis.
  
  

Primary Scratch Don'ts

• If possible, you should designate a different scratch disk than the same drive Photoshop is installed on. Don't use removable media, such as flash drives, for a scratch disk.