RISC iX is a discontinued Unix operating system designed to run on a series of workstations based on the Acorn Archimedes microcomputer. Heavily based on 4.3BSD, it was initially completed in 1988, a year after Arthur but before RISC OS. It was introduced in the ARM2-based R140 workstation in 1989, followed up by the ARM3-based R200-series workstations in 1990. Features Acorn chose BSD 4.3 as the basis for RISC iX due to its academic origins, these being considered as making the software more appropriate for Acorn's principal target market of tertiary education. SunOS and NeXTSTEP systems were given as examples of other "modern high-performance workstations that use BSD". Other reasons for choosing BSD included better integration of networking and connectivity tools in comparison to System V. X11 (initially Release 2) with Ardent Window Manager, Tab Window Manager and Ultrix Window Manager available by default, plus X.desktop from IXI Limited System V virtual memory extensions, compatible with the "System V Interface Definition" C Compiler with ANSI C and Portable C Compiler (pcc) (Berkeley) compatibility Sun Microsystems Network File System version 3.2 ARM assembly language Although Acorn had licensed Sun Microsystems' NeWS in 1987, broad industry adoption of the X Window System, including Sun's belated endorsement, resulted in X11 technologies featuring in RISC iX. RISC iX 1.2 upgraded the X11 server to release 4, and was certified to conform to the X/Open Portability Guide 3 Base profile. Peculiarly, the system console featured a two-cursor text copying mechanism inspired by Acorn's own earlier 8-bit range including the BBC Micro. One reason given for the inclusion of this feature was to be able to provide command line editing facilities for shells that did not offer it and to compensate for the exclusion of shells that did. Architecture-related features The system implemented transparent demand paging of compressed executable programs, allowing the constituent pages of these compressed executables to be loaded into memory by the existing demand paging mechanism and then expanded in place for execution, taking advantage of the availability of sparse files (files with zero-padded regions) to reduce the disc space occupied by these pages. Shared library support, enabling processes to share library code, was also introduced to work around other "unpleasant" consequences of the hardware's 32 KB page size, one of these being the excess space occupied by processes residing in main memory, especially in situations where separate pages need to be allocated.