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[[Image:Symboscpcsymbos21cpc.gif|thumb|320px|Screenshot of the SymbOS desktop running on the Amstrad CPC]] [[Image:Symbos-msx2symbos21msx.gif|thumb|320px|SymbOS MSX running on a MSX2 computer; all applications are platform independant]] [[Image:Symbos-pcwsymbos21pcw.gif|thumb|320px|SymbOS PCW is the third port to a different Z80 system and supports a screen resolution of 720x255]]

'''SymbOS''' is a free multitasking operating system for Z80 based 8-bit computer systems written by [[Prodatron|Prodatron]]. At present it is available for the computers of the Amstrad CPC as well as for all [[MSX ]] models starting from the MSX2 standard and all Amstrad [[PCW|PCW]] (Joyce) models until the PcW10. Contrary to early 8-bit operating systems it is based on a microkernel, which provides pre-emptive and priority oriented multitasking and manages RAM memory with a size of up to 1024 kB. SymbOS contains a MS-Windows like GUI, supports hard discs with a capacity of up to 128 GB and can already be booted on an unexpanded Amstrad CPC-6128, [[PCW|PCW]] or a 128K-MSX2.

Already in the 80's, only few years after the release of the [[Commodore C6464]], the legendary [http://en.wikipedia.org/wiki/GEOS_%288-bit_operating_system%29 GEOS] by Berkeley Softworks appeared and set the standard for a windows-based operating system on c64. It was a graphical user-interface (GUI) which was similar to the old desktop of the Apple Macintosh. Powerfull applications were made available for GEOS like GeoWrite (similar to MS-Word) or GeoCalc (similar to MS-Excel). It was incredible, that an 8bit-machine with only 64K was able to realize such an operating system.

Therefore, the CPC's own OS (in combination with AmsDOS), and [[CP/M|CP/M]] (plus) and FutureOS (since 1989) were the only two known OSes for the series, but the question remained: since most CPCs have 128K (most C64 only have 64K), a screen-resolution of 320x200 with 4 colours (C64 only has 2 colours for each 8x8 area in 320x200) and some more advantages, why not have something similar? So the SymbOS-Project was born. SymbOS stands for "SYmbiosis Multitasking Based Operating System". SymbOS is a demonstration of what has been achieved on the CPC: real preemptive multitasking, dynamic memory-management for up to 1024K and a totaly MS-Windows-like GUI are the three most important features.

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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/M operating system already proved, that multitasking on Z80 computers is possible, but it was not executable on home computers. Today different implementaions of multitasking OS exists for Z80 based systems e.g. Roseanne for the PcW or Doors for the Spectrum.

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.

**Maximum possible screen resolution: 16.000 x × 16.000 pixel

**Source code size (OS Release 2): ~ 4449.000 lines (1,3MB.5&nbsp;MB) **Source code size (Applications): ~ 4870.000 lines (2,0MB.2&nbsp;MB) **Total size of the Z80 source code: ~ 92119.000 lines (3.3MB7&nbsp;MB)

**Amstrad [[CPC|CPC]]-464, -664 and -6128 (unexpanded) and compatibles ([[CPC TREX|CPC TREX]], [[C-ONE|C-ONE]])

**[[SYMBiFACE II|SYMBiFACE II]] (realtime clock, runs in binary mode; PS/2 mouse; IDE interface, Ram/Rom expansion)

The [[Graphical User Interface|GUI ]] of SymbOS works completely object-oriented. Regarding the look and feel it is designed like MS windows. It contains the well-known task bar with the clock and the "start" menu and can open a big amount of windows, which can be shifted, resized and scrolled. As the complete system is written in optimized assembler, the speed of the GUI is only insignificantly under this of current systems and even faster than the original Amiga workbench.

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*[http://www.symbos.de SymbOS homepage]*[http://members.home.nl/evanzanten/msxorg/SymbOS%203%20install%20user%20and%20install%20guide.pdf SymbOS installation configuration manual (PDF)]

[[Category:SymbOS| ]] [[Category:Operating_System]] [[Category:CPC_GUI]] [[Category:Extended RAM Software]] [[Category:PCW]]