Editing CDC 6600 (section)

==CDC 7600==
{{Main|CDC 7600}}
The [[CDC 7600]] was originally{{When|date=May 2022}} intended to be fully compatible with the existing 6000-series machines as well; it started life known as the CDC 6800. But during its design, the designers determined that maintaining complete compatibility with the existing 6000-series machines would limit how much performance improvement they could attain and decided to sacrifice compatibility for performance. While the CDC 7600's CPU was basically instruction compatible with the 6400 and 6600 CPUs, allowing code portability at the [[High-level programming language|high-level language]] source code level, the CDC 7600's hardware, especially that of its Peripheral Processor Units (PPUs), was quite different, and the CDC 7600 required a different operating system. This turned out to be somewhat serendipitous because it allowed the designers to improve on some of the characteristics of the 6000-series design, such as the latter's complete dependence on Peripheral Processors (PPs), particularly the first (called PP0), to control operation of the entire computer system, including the CPU(s). Unlike the 6600 CPU, the CDC 7600's CPU could control its own operation via a Central Exchange jump (XJ) instruction that swapped all register contents with core memory. In fact, the 6000-series machines were [[Retrofitting|retrofitted]] with this capability.