Editing IBM 801 (section)

===Original concept===
In 1974, IBM began examining the possibility of constructing a [[telephone switch]] to handle one million calls an hour, or about 300 calls per second. They calculated that each call would require 20,000 instructions to complete, and when timing overhead and other considerations were added, such a machine required performance of about 12 MIPS.{{sfn|Cocke|Markstein|1990|p=4}} This would require a significant advance in performance; their current top-of-the-line machine, the [[IBM System/370 Model 168]] of late 1972, offered about 3 MIPS.<ref>{{cite web |url=https://alt.folklore.computers.narkive.com/9nl6cj2Q/on-the-370-165-and-the-360-85 |title= On the 370/165 and the 360/85 |first= John |last= Savard}}</ref>

The group working on this project at the [[Thomas J. Watson Research Center]], including [[John Cocke (computer scientist)|John Cocke]], designed a processor for this purpose. To reach the required performance, they considered the sort of operations such a machine required and removed any that were not appropriate. This led to the removal of a [[floating-point unit]] for instance, which would not be needed in this application. More critically, they also removed many of the instructions that worked on data in [[main memory]] and left only those instructions that worked on the internal [[processor register]]s, as these were much faster to use and the simple code in a telephone switch could be written to use only these types of instructions. The result of this work was a conceptual design for a simplified processor with the required performance.{{sfn|Cocke|Markstein|1990|p=4}}

The telephone switch project was canceled in 1975, but the team had made considerable progress on the concept and in October IBM decided to continue it as a general-purpose design. With no obvious project to attach it to, the team decided to call it the "801" after the building they worked in. For the general-purpose role, as opposed to the dedicated telephone system, the team began to consider real-world programs that would be run on a typical [[minicomputer]]. IBM had collected enormous amounts of statistical data on the performance of real-world workloads on their machines and this data demonstrated that over half the time in a typical program was spent performing only five instructions: load value from memory, store value to memory, adding fixed-point numbers, comparing fixed-point numbers, and branching based on the result of those comparisons. This suggested that the same simplified processor design would work just as well for a general-purpose minicomputer as a special-purpose switch.{{sfn|Cocke|Markstein|1990|p=5}}