It is important to understand the reason that the 67x series routers run CBOS versus the IOS like all other Cisco products do.

CBOS was not written by Cisco, but is instead a slighly changed version of NBOS (Netspeed Broadband OS). Since the design of the 675, the first and still core 67x model, was bought from NetSpeed, Cisco also bought the rights to its OS and changed all references to the company name found therein. It is based on the i960 processor which is not a CPU used by any other Cisco products (and is not natively IOS compatible), though there have been rumours that Cisco is still commited to porting IOS to it.