It includes two 24-bit registers, which can also be referred to as a single 48-bit register. It also includes two 56-bit accumulators, each with an 8-bit "extension" (aka headroom); otherwise, the accumulators are similar to the other 24/48-bit registers. Being a Modified Harvard architecture processor, the 56k has three memory spaces+buses (and on-chip memory banks in some of the models): a program memory space/bus and two data memory space/bus.[1]