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 registers for all computations and eliminating the many variant addressing modes found in 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 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.

The 801 was extremely influential in the computer market.^{[citation needed]} Armed with huge amounts of performance data, IBM was able to demonstrate that the simple design was able to easily outperform even the most powerful classic CPU designs, while at the same time producing machine code that was only marginally larger than the heavily optimized CISC instructions. Applying these same techniques even to existing processors like the System/370 generally doubled the performance of those systems as well. 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 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.