Editing IBM 801 (section)

{{Short description|Experimental minicomputer by IBM}}
{{About|the 1970s IBM CPU|the document processor released in 1934|IBM document processors#IBM 801}}
The '''801''' was an experimental [[central processing unit]] (CPU) design developed by [[IBM]] during the 1970s. It is considered to be the first modern [[RISC]] design, relying on [[processor register]]s for all computations and eliminating the many variant [[addressing mode]]s found in [[Complex instruction set computer|CISC]] designs. Originally developed as the processor for a [[telephone switch]], it was later used as the basis for a [[minicomputer]] and a number of products for their [[mainframe computer|mainframe]] line. The initial design was a [[24-bit]] processor; that was soon replaced by [[32-bit]] implementations of the same concepts and the original 24-bit 801 was used only into the early 1980s.

During the initial design the system was considered as a simple processor with limited functionality that would not compete with IBM's more complex systems like the [[System/370]]. But as they explored the concept using huge amounts of performance data collected from their customers, the team was able to demonstrate that the simple design was able to easily outperform even the most powerful classic CPU designs. Applying these same techniques to existing machines like the S/370, that is, ignoring the many complex [[opcode]]s in favour of doing everything it could in registers, doubled the performance of those systems as well. The complexity of these older designs actually led to slower and much more costly machines, spending considerable complexity implementing codes that were better left unused. This demonstrated the value of the RISC concept, and all of IBM's future systems were based on the principles developed during the 801 project.

For his work on the 801, [[John Cocke (computer scientist)|John Cocke]] was recognized with several awards and medals, including the [[Turing Award]] in 1987, [[National Medal of Technology]] in 1991, and the [[National Medal of Science]] in 1994.