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remain at their original length, so the processor cannot directly span all of bank-switched memory by, for example, incrementing an internal register. Instead the processor must explicitly do a bank-switching operation to access large memory objects. There are other limitations. Generally a bank-switching system will have one block of program memory that is common to all banks; no matter which bank is currently active, for part of the address space only one set of
29:
325:
235:. 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 KB each. Blocks of various sizes were switched in and out via bank select registers or similar mechanisms.
356:
joined for versions 3.2 in 1986 and 4.0 in 1987 and the specification became known as Lotus-Intel-Microsoft EMS or LIM EMS. It is a form of bank switching technique that allows more than the 640 KB of RAM defined by the original IBM PC architecture, by letting it appear piecewise in a 64 KB
165:
Often a single database spans several banks, and the need arises to move records between banks (as for sorting). If only one bank is accessible at a time, it would be necessary to move each byte twice: first into the common memory area, perform a bank switch to the destination bank, and then actually
152:
of the processor, it does not automatically change state when the program counter overflows; this cannot be detected by the external latch since the program counter is an internal register of the processor. The extra memory is not seamlessly available to programs. Internal registers of the processor
36:
of bank-switched memory for a processor that can only address 64 KB. This scheme shows 200 KB of memory, of which only 64 KB can be accessed at any time by the processor. The operating system must manage the bank-switching operation to ensure that program execution can continue when
486:
to swap active banks, so that the transition visible on screen is free of artifacts or distortion. In this case, the processor may have access to all the memory at once, but the video display hardware is bank-switched between parts of the video memory. If the two (or more) banks of video memory
481:
may be used to improve video performance. In this case, while the processor is updating the contents of one set of physical memory locations, the video generation hardware is accessing and displaying the contents of a second set. When the processor has completed its update, it can signal to the
91:, where the addresses generated are narrower than the address bus width. Some control-oriented microprocessors use a bank-switching technique to access internal I/O and control registers, which limits the number of register address bits that must be used in every instruction.
177:
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. The application program must keep track of which
424:
contained their own bank switching hardware in order to permit the use of more ROM and thus allow for more sophisticated games (via more program code and, equally important, larger amounts of game data such as graphics and different game stages). The
400:, from the perspective of a program that uses it. Later versions of MS-DOS (starting circa version 5.0) included the EMM386 driver, which simulates EMS memory using XMS, allowing programs to use extended memory even if they were written for EMS.
126:
The follow-on system to a processor with a 15 bit address has an 18 bit address bus, but legacy instructions only have 15 address bits; internal bank registers can be used to provide those bits. Some new instructions can explicitly specify the
316:. This allows short instruction words to save space during routine program execution, at the cost of extra instructions required to access relatively infrequently used registers, such as those used for system configuration at start-up.
122:
The follow-on system to a processor with a 12 bit address has a 15 bit address bus, but there is no way to directly specify the high three bits on the address bus. Internal bank registers can be used to provide those
86:
systems. Bank-switching may also be used to work around limitations in address bus width, where some hardware constraint prevents straightforward addition of more address lines, and to work around limitations in the
395:
processors in which MS-DOS runs. XMS allows extended memory to be copied anywhere in conventional memory, so the boundaries of the "banks" are not fixed, but in every other way it works like the bank switching of
182:
holds a required piece of data, and then call the bank-switching routine to make that bank active. However, bank-switching can access data much faster than, for example, retrieving the data from disk storage.
312:(microprocessors with significant input/output hardware integrated on-chip) may use bank switching, for example, to access multiple configuration registers or on-chip read/write memory. An example is the
146:, an output address may be decoded. Several bank-switching control bits could be gathered into a register, approximately doubling the available memory spaces with each additional bit in the register.
487:
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.
142:
The latch can be set or cleared by the processor in several ways; a particular memory address may be decoded and used to control the latch, or, in processors with separately-decoded
510:. 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.
254:, 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,
1010:
56:
from diskette could be switched out when no longer needed. In video game systems, bank switching allowed larger games to be developed for play on existing consoles.
281:
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
102:. Data remains in quiescent storage in a memory area that is not currently accessible to the processor (although it may be accessible to the video display,
301:) to access separate RAM banks, allowing programmers to make large playfields and other graphic objects without using up the memory visible to the CPU.
170:
engine or a second CPU, and its bank access restrictions differ, whichever subsystem can transfer data directly between banks should be used.
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handheld from
Gamepark Holdings uses bank switching in order to control the start address (or memory offset) for the second processor.
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is a technique used in computer design to increase the amount of usable memory beyond the amount directly addressable by the
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addresses, could be accessed. The processor could change which set is in current use by setting or clearing the latch bit.
445:
cartridges used a chip called MBC (Memory Bank
Controller), which not only offered ROM bank switching, but also cartridge
426:
397:
380:
278:
supported bank switching to allow use of more than the 64 KB of memory that the 8080 or Z80 processor could address.
383:(XMS), also now obsolete, is a standard for, in principle, simulating bank switching for memory above 1 MB (called "
88:
446:
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were over 4 MB in size and required the use of this technique (4 MB being the maximum address size). The
191:
157:
will be used. This area would be used to hold code that manages the transitions between banks, and also to process
239:
was the first microcomputer manufacturer to use bank switching, supporting 8 banks of 64 KB in its systems.
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A processor with a 16-bit external address bus can only address 2 = 65536 memory locations. If an external
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361:. The 64 KB is divided into four 16 KB "pages" which can each be independently switched. Some
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45:
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167:
103:
72:
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An eight-position DIP switch on such cards is used to select one (or more) of eight banks of memory.
136:
was added to the system, it could be used to control which of two sets of memory devices, each with
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430:
313:
133:
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With memory bank select, memory space is arranged in a number of separate banks of up to 64K each.
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instructions. It can be used to configure a system differently at different times; for example, a
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When using bank switching some caution was required in order not to corrupt the handling of
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memory board was used to map the memory into one or more of eight distinct 64 KB banks.
49:
148:
Because the external bank-selecting latch (or register) is not directly connected with the
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or rumble motors. Bank switching was still being used on later game systems. Several Sega
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used bank switching to allow for a full 64 KB of RAM and still provide for ROM and
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Cromemco was the first microcomputer manufacturer to refine and exploit bank switching.
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106:, or other subsystems of the computer) without the use of special prefix instructions.
68:
28:
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75:, non-volatile memory, input-output devices and system management registers in small
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60:
861:"New 1-2-3 Gets 4 Megabytes of Memory, Lotus, Intel Break PC DOS Memory Barrier".
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to move the byte into the destination bank. If the computer architecture has a
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made use of this, and though EMS is obsolete, the feature is nowadays
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American inventors, entrepreneurs & business visionaries
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Bank switching can be considered as a way of extending the
550:
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to provide backwards compatibility with those programs.
118:
of processor instructions with some register. Examples:
98:, data is not exchanged with a mass storage device like
449:
bank switching, and even access to such peripherals as
404:
emulates XMS also, for those programs that require it.
968:
Hardware hacking: have fun while voiding your warranty
844:(1982-10-25). "Digital Research offers CP/M upgrade".
437:
or more of ROM, addressed via bank switching called a
965:
Grand, Joe; Russell, Ryan; Mitnick, Kevin D. (2004).
897:
The
Handbook of Software for Engineers and Scientists
812:"Share and Share Alike: Multiuser Hardware Explained"
16:
A technique to increase the amount of usable memory
765:
622:Control Data 3600 Computer System Reference Manual
37:part of memory is not accessible to the processor.
924:Sinofsky, Brian (2002). Carey, Charles W. (ed.).
297:could allow its two processors (the 6502 and the
878:"EMS Update Gives DOS Improved Multitasking".
670:
668:
603:Control Data 160-A Computer Programming Manual
387:"), which is not directly addressable in the
8:
1007:"Story about bank switching in the Apple II"
768:Introduction to Microprocessor System Design
714:"Design Innovations in Personal Computers"
577:Computer structures: readings and examples
433:but its cartridges sometimes contained a
573:Bell, C. Gordon; Newell, Allen (1971).
540:
495:Bank switching was later supplanted by
266:3.0 released in 1983 and the Z80-based
820:. Vol. 3, no. 11. p. 18
609:. CDC. March 1963. p. 2-09. 145e.
522:, an example of bank switching on the
412:Bank switching was also used in some
7:
491:Alternative and successor techniques
344:Specification (EMS) 3.0 for use in
681:(2 ed.). Que Books. pp.
231:can directly address only 64
14:
1013:from the original on 2020-12-12.
552:. CUP Archive. pp. 47–50.
223:, etc.) commonly used in early
79:. The technique was common in
1:
712:Garland, Harry (March 1977).
427:Nintendo Entertainment System
381:eXtended Memory Specification
328:Expanded memory in the IBM PC
71:use bank switching to manage
59:Bank switching originated in
503:, which in turn gave way to
94:Unlike memory management by
895:Ross, Paul W., ed. (1995).
678:Upgrading and Repairing PCs
477:, the related technique of
1057:
810:Hogan, Thom (1981-06-08).
548:Aspinall, D., ed. (1978).
473:In some types of computer
18:
1019:"What Is Bank Switching?"
774:McGraw-Hill Book Company
357:"window" located in the
19:Not to be confused with
764:Garland, Harry (1979).
734:10.1109/c-m.1977.217669
675:Mueller, Scott (1992).
643:Embedded systems design
508:memory management units
459:Super Street Fighter II
439:Multi-Memory Controller
332:In 1985, the companies
520:Sideways address space
484:video display hardware
329:
200:
195:Bank select switch on
38:
971:. Syngress. pp.
726:IEEE Computer Society
639:Heath, Steve (2003).
529:Overlay (programming)
429:contained a modified
327:
194:
63:systems. Many modern
31:
457:cartridges, such as
73:random-access memory
932:Infobase Publishing
647:. Newnes. pp.
600:"Storage Control".
414:video game consoles
408:Video game consoles
314:PIC microcontroller
285:. For example, the
225:video game consoles
348:computers running
330:
201:
39:
1041:Memory management
628:. CDC. 60021300E.
402:Microsoft Windows
374:operating systems
371:Microsoft Windows
359:Upper Memory Area
346:IBM PC compatible
291:memory-mapped I/O
187:Microcomputer use
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342:Expanded Memory
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150:program counter
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69:microprocessors
32:A hypothetical
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903:. p. 26.
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104:DMA controller
54:start a system
42:Bank switching
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867:. 1985-04-29.
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850:. p. 1.
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836:
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822:. Retrieved
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497:segmentation
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100:disk storage
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61:minicomputer
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52:required to
41:
40:
25:
934:. pp.
585:. pp.
583:McGraw Hill
340:introduced
295:Atari 130XE
283:address bus
260:I/O devices
180:memory bank
1030:Categories
988:2020-02-08
951:2020-02-08
824:2020-02-08
793:2020-02-08
776:. p.
747:2020-02-08
698:2020-02-08
535:References
455:Mega Drive
418:Atari 2600
379:The later
320:The IBM PC
248:interrupts
244:subroutine
159:interrupts
34:memory map
901:CRC Press
881:InfoWorld
864:InfoWorld
847:InfoWorld
817:InfoWorld
524:BBC Micro
389:Real Mode
369:by later
354:Microsoft
173:Unlike a
110:Technique
46:processor
1011:Archived
742:32243439
718:Computer
514:See also
499:in many
443:Game Boy
367:emulated
276:Model II
237:Cromemco
197:Cromemco
936:322–324
683:699–700
435:megabit
272:Model 4
268:TRS-80s
264:CP/M-80
262:, etc.
246:calls,
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907:
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728:: 25.
689:
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505:paging
416:. The
350:MS-DOS
250:, the
205:16-bit
96:paging
21:Paging
738:S2CID
724:(3).
626:(PDF)
607:(PDF)
338:Intel
334:Lotus
299:ANTIC
138:65536
134:latch
127:bank.
123:bits.
81:8-bit
977:ISBN
940:ISBN
905:ISBN
782:ISBN
687:ISBN
653:ISBN
554:ISBN
463:GP2X
447:SRAM
431:6502
336:and
274:and
270:the
227:and
221:6809
217:6502
209:8080
67:and
973:229
730:doi
649:242
587:156
398:EMS
393:x86
391:of
287:C64
256:DMA
213:Z80
168:DMA
89:ISA
50:ROM
1032::
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