list of Gestalt IDs returned with various logic board modifications (speed as reported by Newer Technology's "Clockometer") are as follows System software A standard Quadra 605 is capable of running classic Mac OS versions 7.1, 7.1.1 (Pro), 7.5, 7.5.1, 7.5.3, 7.5.5, 7.6, 7.6.1, 8.0, and 8.1. With a PowerPC upgrade installed, it can run 8.5, 8.5.1, 8.6, 9.0, 9.0.1, 9.0.2, 9.0.3, 9.0.4 and 9.1. Versions of the System Software below 7.5 require the use of System Enabler 065. If a Quadra 605 is running a version of System 7.1, over-clocking it from the standard 25 MHz to 33 MHz will change the Gestalt ID, but the enabler will recognize the new ID. Under-clocking to 20 MHz, however, will change the Gestalt ID to one the enabler doesn't recognize as compatible, and the system won't boot. System 7.5 or later is not affected by this issue. Timeline References External links Quadra 605 profile at lowendmac.com Quadra 605 at everymac.com Quadra 605 at apple-history.com Quadra 605 Specifications Repair and Upgrades 605 0605 Quadra 605 Quadra 605 Quadra 605 Quadra 605 Computer-related introductions in 1993