Cyril Blanc said: >After MAC OS X has install an APP, you have a message that it is >"optimizing System Performance" > >What is it doing ? It is doing what is known as "pre-binding". That is, when a program launches under OS X, it automatically opens a bunch of supporting files. Prebinding speeds up application launch in the future by creating a "list" of what files are needed to launch an application, where they reside on the disk, and the order they need to be read and loaded. http://docs.info.apple.com/article.html?artnum=106271 Item #3 http://www.kernelthread.com/mac/apme/optimizations/#SIX Randy B. Singer Co-Author of: The Macintosh Bible (4th, 5th and 6th editions) Routine OS X Maintenance and Generic Troubleshooting http://www.macattorney.com/ts.html