Editing Bank switching (section)

== Microcomputer use ==
[[File:Bank Select Switch on Cromemco Memory Board.jpg|thumb|Bank select switch on [[Cromemco]] memory board was used to map the memory into one or more of eight distinct 64&nbsp;KB banks.<ref name="Garland_1977"/>]]

Processors with [[16-bit]] addressing ([[8080]], [[Z80]], [[6502]], [[6809]], etc.) commonly used in early [[video game console]]s and [[home computer]]s can directly address only 64&nbsp;[[kilobyte|KB]]. Systems with more memory had to divide the address space into a number of blocks that could be dynamically mapped into parts of a larger address space. Bank switching was used to achieve this larger address space by organizing memory into separate banks of up to 64&nbsp;KB each.<ref name="Garland_1979"/> Blocks of various sizes were switched in and out via bank select registers or similar mechanisms. [[Cromemco]] was the first microcomputer manufacturer to use bank switching, supporting 8 banks of 64&nbsp;KB in its systems.<ref name="Hogan_1981"/>

When using bank switching some caution was required in order not to corrupt the handling of [[subroutine]] calls, [[interrupt]]s, the [[call stack|machine stack]], and so on. While the contents of memory temporarily switched out from the CPU was inaccessible to the processor, it could be used by other hardware, such as video display, [[direct memory access|DMA]], [[Input/output|I/O devices]], etc. [[CP/M Plus|CP/M-80]] 3.0 released in 1983 and the Z80-based [[TRS-80]]s the [[TRS-80 Model 4|Model 4]] and [[TRS-80 Model II|Model II]] supported bank switching to allow use of more than the 64&nbsp;KB of memory that the 8080 or Z80 processor could address.<ref name="Freiberger_1982"/>

Bank switching allowed extra memory and functions to be added to a computer design without the expense and incompatibility of switching to a processor with a wider [[address bus]]. For example, the [[Commodore 64|C64]] used bank switching to allow for a full 64&nbsp;KB of RAM and still provide for ROM and [[memory-mapped I/O]] as well. The [[Atari 8-bit computers|Atari 130XE]] could allow its two processors (the 6502 and the [[ANTIC]]) to access separate RAM banks, allowing programmers to make large playfields and other graphic objects without using up the memory visible to the CPU.