sentence: features risc ix running on the acorn a680 x11 ( initially release 2 ) with ardent window manager , tom 's window manager and ultrix window manager available by default system v virtual memory extensions , compatible with the '' system v interface definition '' c compiler with ansi c and pcc ( berkeley ) compatibility sun network file system version 3.2 arm assembler later versions upgraded the x11 server to release 4 , and was certified to conform to the x/open portability guide 3 base profile .