QuickTime VM is a system extension which attempts to make QuickTime work in a more friendly manner when virtual memory is turned on in your machine. If you have virtual memory turned off, the extension should have no effect. To install QuickTime VM, simply drag its icon on top of your System Folder icon, or place it manually in the Extensions folder within your System Folder. Once this is done, restart your system.
Note that because of the way this extension works, you may need to increase the amount of memory you give to QuickTime applications. To adjust the memory size, select the application in the Finder, choose Get Info from the File menu, and type a larger number in the preferred size box.
IMPORTANT: When running with virtual memory turned on, do *NOT* set the preferred size to a number larger than the amount of real RAM you have in your system. Otherwise, you will defeat the purpose of the QuickTime VM extension!
Why QuickTime has trouble with VM: normally, when QuickTime is decompressing an image, it creates a large temporary buffer to store the decompressed data in before it copies that data to your screen. Because these buffers can be large, QuickTime will try to use free memory in the system, which you probably have a lot of when you are running with virtual memory turned on. Because these large buffers can be bigger than the amount of real RAM in your system, it can cause a huge amount of disk activity as the image is decompressed.
Why QuickTime VM fixes the problem: The QuickTime VM extension prevents QuickTime from allocating these temporary buffers in the system's free memory. This will force QuickTime to create its buffers in the free memory available to the application that is using QuickTime instead, which is why you may need to give your QuickTime applications more memory when the extension is installed.
