By now you've probably noticed that the importance of RAM previews. There is the standard one which you normally see in the Time Control Window and can be invoked by pressing 0 on the numeric keypad.
The other RAM Preview controls can be accessed by click on the words "RAM Preview Options." This preview is usually a lower quality method, but can be configured to the user 's preference. To launch this alternate preview, Shift + click on the Preview button or press Shift + 0 on the numeric keypad.