Editing Burroughs Large Systems (section)

===Stack speed and performance===
Stack performance was considered to be slow compared to register-based architectures, for example, such an architecture had been considered and rejected for the [[IBM System/360|System/360]].<ref>{{Cite journal |author=G. M. Amdahl |author2=G. A. Blaauw |author3=F. P. Brooks |url=https://www.researchgate.net/publication/220498837 |title=Architecture of the IBM System/360 |journal=IBM Journal of Research and Development |volume=8 |issue=2 |date=April 1964 |pages=87–101 |doi=10.1147/rd.82.0087 |access-date=2021-09-10 |via=ResearchGate}}</ref> One way to increase system speed is to keep data as close to the processor as possible. In the B5000 stack, this was done by assigning the top two positions of the stack to two registers A and B. Most operations are performed on those two top of stack positions. On faster machines past the B5000, more of the stack may be kept in registers or cache near the processor.

Thus the designers of the current successors to the B5000 systems can optimize in whatever is the latest technique, and programmers do not have to adjust their code for it to run faster – they do not even need to recompile, thus protecting software investment. Some programs have been known to run for years over many processor upgrades. Such speed up is limited on register-based machines.{{Citation needed|date=January 2010}}

Another point for speed as promoted by the RISC designers was that processor speed is considerably faster if everything is on a single chip. It was a valid point in the 1970s when more complex architectures such as the B5000 required too many transistors to fit on a single chip. However, this is not the case today and every B5000 successor machine now fits on a single chip as well as the performance support techniques such as caches and instruction pipelines.

In fact, the A Series line of B5000 successors included the first single chip mainframe, the Micro-A of the late 1980s. This "mainframe" chip (named SCAMP for Single-Chip A-series Mainframe Processor) sat on an Intel-based plug-in PC board.