The simplest way to clean-boot the operating system was to hold the shift key: loading of extensions would be bypassed. System 7.5 added the Extensions Manager, which allowed the user to quickly enable or disable particular extensions, and also to define sets of them that would work correctly together. Extensions Manager came with two read-only base sets provided: one that contained the subset of extensions needed for basic OS operation, and one that enabled all the official extensions that shipped with the OS but disabled all third-party extensions.