Page <a href="http:&#x2F;&#x2F;www.symbos.de&#x2F;facts.htm" rel="nofollow">http:&#x2F;&#x2F;www.symbos.de&#x2F;facts.htm</a>, end of the third paragraph &quot;Real preemptive Multitasking, a dynamic memory-management for up to 576K and more and a totaly MS-Windows-like GUI are the three most important things.&quot;<p>I&#x27;m also a little puzzled about real preemption on a Z80, but <a href="http:&#x2F;&#x2F;www.cpcwiki.eu&#x2F;index.php&#x2F;SymbOS#Technical_background" rel="nofollow">http:&#x2F;&#x2F;www.cpcwiki.eu&#x2F;index.php&#x2F;SymbOS#Technical_background</a> states<p>&quot;Even the Z80 8-bit CPU is able to run a pre-emptive multitasking environment. Missing mechanisms like memory protection, which are often called as a condition for multitasking, are system stability issues only. The MP&#x2F;M operating system already proved, that multitasking on Z80 computers is possible.<p>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. &quot;