The PowerBook VM Tuner enhances system stability while using virtual memory on your PowerBook 1400. During the manufacturing process, the PowerBook VM Tuner file is preloaded into the System Folder on your hard disk, but it is not part of the "Install Mac OS" system software installer. Therefore, if you reinstall the Mac OS 7.6 system software, you may need to manually reinstall the PowerBook VM Tuner file.