The MBus frequency can be set using OpenBoot firmware commands, to 40, 50, 60, 66 or even 75MHz. However, early HyperSTATION-30 motherboards do not run reliably above 50MHz; later ones run reliably at 60MHz; and the latest ones are rumoured to be reliable at 66MHz. See Whither the High-Speed MBus?
Note that modules with 256Kb cache (per CPU), or slower than 125MHz, or faster than 166MHz, or bus-clocked modules with a multiplier greater than 3, are not officially supported on an MBus faster than 50MHz, although in some cases they may work (the problem appears to lie in the allowed geometry of the MBus traces on the system-board or the capacitive properties of the MBus module-connector - prototypes with HyperSPARC chips soldered directly onto an MBus motherboard would operate reliably at 70MHz with an RT521/523 chipset.
|Module Type||No. of
|Functional?||Min. PROM level||Heat Rating|
|Mike Spooner, revised 28th December 2001|