Actually, rogergordian, the hard drive does play a part in memory as well - the swap file. As the RAM gets filled up, some of the information is put on the hard drive, in an area reserved for back-up to the RAM. It's not as fast as the RAM, but it's faster than searching for all the bits scattered about the hard drive. When you shut down your machine, the OS clears out the swap file. The next time you turn your computer on, it recreates the swap file. Depending on your OS and your settings, your computer might always have X amount for swap file space, or it may be set to use up to X amount or X percentage of hard drive space. If your hard drive is full or nearly full, it will affect how your computer runs because it doesn't have enough space left to create the swap file. I have a 4 GB partition set up just for swap space to make sure that I don't run out. It works quite well. Pardon a young tech giving this mini-lesson.