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SymbOS is a multitasking operating system for Zilog Z80-based 8-bit computer systems. Contrary to early 8-bit operating systems it is based on a microkernel, which provides pre-emptive and priority oriented multitasking and manages RAM with a size of up to 1024 KB. SymbOS contains a Microsoft Windows like Graphical user interface, supports hard disks with a capacity of up to 128 GB and can already be booted on an unexpanded Amstrad CPC-6128, a 128K-MSX2 and an Amstrad PCW. At present it is available for the Amstrad CPC series of computers, as well as for all MSX models starting from the MSX2 standard and for most Amstrad PCW models.〔 == Motivation and rationale == SymbOS was originally started as an experiment to find out to what extent it is possible to implement a multitasking based operating system with a windowed GUI on an 8-bit computer from 1985. GEOS contributed to the motivation, but the structure and features of SymbOS aren't similar to that system. The release in 2006 proved that such a "mini windows" system is possible on an at the time 20-year-old home computer with only quantitative limitations. SymbOS is one of the largest retro computing software projects of recent years. One of the goals of the project is to allow these old machines to be used like a modern PC, using hardware extensions. Although only an 8-bit CPU, the Z80 is capable of running a pre-emptive multitasking operating system. Features such as memory protection, which the Z80 does not support, are not essential in such an OS. For example, AmigaOS does not feature memory protection either. The MP/M OS proved that multitasking on the Z80 CPU was possible; however, it was not generally available for home computers. While the MOS Technology 6502 cannot move the stack pointer, the Z80 can freely relocate it to any position in memory, which makes it easier to implement pre-emptive multitasking. The existence of an alternative register set accelerates context switching between tasks dramatically. The restriction of Z80 system 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 hundreds or thousands of kilobytes of memory. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「SymbOS」の詳細全文を読む スポンサード リンク
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