


You can configure if you want a page file on a particular drive, and if so if you want a fixed page file or one that changes size as needed. When you alt-tab / go back to that previous application, the operating system will read the data of that application from the page file and put it back in ram. if your memory is full or nearly full by some applications and you launch an application or a game that needs more ram than it's free in the actual ram, Windows can take the data of applications that are in background or accessed a longer time ago and dumps that data in the page file, making room for your new application/game. Like the others said, it's page file, swap.
