If you’re so inclined, you can still boot MS-DOS 3.3 on the latest generation of Core Duo, Xeon, AMD64 and Opteron processors. Why? Because while the amount of core instructions increased in order to support new features (such as protected mode), the instruction word length increased from 16 to 32 to 64 bits, the amount of memory that the processor could use increased geometrically, and the number of processor cores increased, and the bus technology improved to handle higher speeds, at the end of the day, the basic architecture is fundamentally no different than what we started with in 1981. So why exactly do we still need systems than can still run CP/M and DOS on the metal?