risc os
     
        reduced instruction set computer operating system acorn
        computers' operating system for their archimedes family
        of personal computers.  risc os replaced the arthur
        operating system used on the first archimedeses.  it is
        written in arm assembly code and distributed on rom so
        it takes up no disk space and takes no time to load.  it
        supports cooperative multitasking with memory management and
        includes a graphical user interface or "wimp".  it is
        written in a highly modular style and makes extensive use of
        vectors so it is easy to modify and extend by loading new
        modules in ram.  a large number of system calls called
        "swis" - software interrupts are available to the
        applications programmer and some of these are available as
        user comands via a built-in command-line interpreter.  risc
        os also supported outline fonts when only bitmap fonts
        were available on most other platforms.
     
     
see also:
acorn computers operating system archimedes personal computer arthur arm 
assembly code rom cooperative multitasking graphical user interface vector 
ram system call command-line interpreter outline font bitmap font 
platform