Bank switching

Unlike a virtual memory scheme, bank-switching must be explicitly managed by the running program or operating system; the processor hardware cannot automatically detect that data not currently mapped into the active bank is required.

[9] When using bank switching some caution was required in order not to corrupt the handling of subroutine calls, interrupts, the 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, DMA, I/O devices, etc.

For example, the C64 used bank switching to allow for a full 64 KB of RAM and still provide for ROM and memory-mapped I/O as well.

In 1985, the companies Lotus and Intel introduced Expanded Memory Specification (EMS) 3.0 for use in IBM PC compatible computers running MS-DOS.

Some computer games made use of this, and though EMS is obsolete, the feature is nowadays emulated by later Microsoft Windows operating systems to provide backwards compatibility with those programs.

The GP2X handheld from Gamepark Holdings uses bank switching in order to control the start address (or memory offset) for the second processor.

When the processor has completed its update, it can signal to the video display hardware to swap active banks, so that the transition visible on screen is free of artifacts or distortion.

If the two (or more) banks of video memory contain slightly different images, rapidly cycling (page-flipping) between them can create animation or other visual effects that the processor might otherwise be too slow to carry out directly.

Bank switching was later supplanted by segmentation in many 16-bit systems, which in turn gave way to paging memory management units.

In embedded systems, however, bank switching is still often used for its simplicity, low cost, and often better adaptation to those contexts than to general purpose computing.