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SymbOS

178 bytes removed, 01:28, 16 February 2009
A stack is not a prerequisite for multitasking. For example take a look at IBMs MVS XESA (late 80ies, beginning 90ies). The used CPUs emulated a stack by software!
== Technical background ==
The Z80 8-bit CPU is able to run a pre-emptive multitasking environment. The MP/M operating system already proved, that multitasking on Z80 computers is possible.
While the MOS Technology 6502 can not move the stack, the Z80 can freely replace it to any position in the memory, which is more or less a condition for pre-emptive multitasking. The existance of an alternative register set accelerates the content switching between the tasks dramatically. The restriction of Z80 systems to a 64 kB address space can be solved with bank switching. In this way computers like the Amstrad CPC and PCW, MSX, Enterprise or SAM Coupé are able to access hundred or thousand of kilobytes of memory.
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