How Virtual Memory Works on Your PC - dummies

How Virtual Memory Works on Your PC

By Mark L. Chambers

Pseudo-RAM called virtual memory actually exists on your hard drive rather than as memory modules on your motherboard. Modern operating systems (Windows 8/7/Vista/XP, Mac OS X, Unix, and Linux) all use the virtual memory trick to feed your applications the memory they need.

Suppose that your PC has only 2GB of random access memory (RAM) installed, but you just ran Photoshop and demanded that it load two 500MB high-resolution digital images. If Windows were limited to using only your computer’s physical RAM (the memory modules you installed on your PC’s motherboard), you would be up a creek because Windows 8 requires a minimum of around 500MB of memory itself, and Photoshop takes a significant chunk of memory to run.

On top of all that, you’d be loading 1GB of data! Considering the size of today’s documents and the amount of RAM needed by memory-hungry mega-applications, your 2GB PC literally couldn’t do its job. And, don’t forget that you’d probably be running more than one application at a time. What’s a computer to do?

As you can see, Windows turns to your hard drive for help. It uses a portion of the empty space on your hard drive to temporarily hold the data that would otherwise be held in your computer’s memory.

In this case, your hardworking silicon warrior uses 2GB of hard drive space, so the total memory available within Windows (using both 2GB of physical memory and 2GB of virtual memory) is now 4GB, providing more elbowroom to work with.

Your programs don’t know that they’re using virtual memory — Windows takes care of everything behind the scenes, so Photoshop thinks that you have 4GB of physical memory.


How much is enough? Try to leave at least 25GB or 30GB free on the C: drive at all times. (Your C: drive is typically the hard drive that Windows 8 boots from. To check how much space it has remaining, display your Desktop and click on the File Explorer icon on the taskbar, and then right-click on the drive you want to check and choose Properties.)

A PC that runs out of hard drive space is a terrible thing to see; applications start to lock up, you might lose any changes you made to open files, and Windows begins displaying pitiful error messages begging you to close some of your open application windows (or even restart).

Also, note that virtual memory is always slower than true physical memory. After all, that data has to be written to and read from your hard drive rather than from superfast memory modules. This is why you should add as much RAM to your PC as possible; the more memory that you add, the less likely that Windows needs to resort to virtual memory.

PC techs call your computer’s use of virtual memory drive thrashing because Windows must continually write data to, read data from, and erase data from your hard drive. When you run out of physical memory, the hard drive activity light on the front of your machine never seems to go out. And yes, if you’re wondering, all that activity shortens the life of your hard drive over time.