You can find scratch disk settings in preferences. For SD cards, a C10 or U3 upwards is always better. If you use a pen drive, it has to be at least a USB 3 drive with Class 10 performance. Bear in mind that the important thing is to use something other than your operating system hard disk to enable parallel writing. If you have more than one hard disk or you can free up a flash drive or if nothing, a fast USB 3.1 pen drive will do. Scratch discs: If you work with big files and photoshop starts to use your hard discs for dumping memory, it’s a good idea to set up scratch discs smartly. Here are some tips that will speed things up, sometimes making a day and night difference. Even a relatively fast computer with modern hardware can face slowdowns if things are not set up correctly or it’s not maintained well. If you are facing lag and slowdown working on photoshop or other applications for that matter, there are some things that you can always do to speed things up.
