I'm going to make this system work a little harder by downloading the installer for Microsoft Office 2010 Professional Plus (beta). As it extracts its installation files, you can see the green In Use bar grow and the blue Standby bar shrink. Note the Committed Bytes counter hasn't changed at all. Here the system is making sure those installation files are ready to run from fast RAM instead of having to be read from a slow disk.
For more details, see Windows 7 memory usage: What’s the best way to measure?