RISC iX is a discontinued Unix operating system designed to run on a series of workstations based on the Acorn Archimedes microcomputer.

Other reasons for choosing BSD included better integration of networking and connectivity tools in comparison to System V.[5] 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.

[7] 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.

[8][9] Peculiarly, the system console featured a two-cursor text copying mechanism inspired by Acorn's own earlier 8-bit range including the BBC Micro.

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.

[12][13] Despite these remedies, the workstations offering RISC iX were regarded as being hampered by the memory management unit (MMU) using 32 KB pages.

[18] Subsequent Archimedes machines, such as the A5000 and A30x0 models, were introduced without any prominent indication of RISC iX compatibility, although the A5000 expansion hardware was designed to support the same form of expansion card interrupt management as the A540, R-series and A400/1-series, specifically to be able to support RISC iX.

Since the hardware is based on the Archimedes series, Acorn's podule expansions could be added, although appropriate drivers would have needed to be written.

These machines were designed to support the FPA device via a dedicated socket on the processor card (or, in the case of the A5000, on the motherboard), and offered a peak throughput of 5 MFLOPS at 26 MHz.

[36] Similar Econet gateway capabilities were eventually extended to computers running RISC OS with Acorn's TCP/IP Protocol Suite product[37] and with the broader Acorn Universal Networking (AUN) suite of technologies,[38] and a device driver update eventually provided a similar means of routing TCP/IP communications over Econet networks for RISC OS machines.

[39] In 1989, Acorn announced support for the R140 from a number of application software vendors, including Informix, along with applications such as Uniplex, Q-Office (from Quadratron), Tetraplan, Sculptor (from MPD), Sea Change (from Thomson),[40] Recital ("a dBase compatible relational database") and Q-Calc ("a Lotus, key-compatible spreadsheet").

[46] With the development of the ARM chipset, however, Acorn was finally in a position to deliver its own system capable of running Unix, announcing work as early as the autumn of 1987 on an "upmarket ARM-based workstation to run the Unix operating system" for release in mid-1988 to compete with Sun and Apollo models in the higher education market, featuring a built-in WE32206 "arithmetic co-processor".

The introduction of the R225 and R260 renewed the enthusiasm of some commentators who conceded that the earlier ARM2-based R140, alongside competition based on the 80386, 68020 and 68030 processors, were underpowered to run "wedding-cake configurations" of the X Window System, Motif, X.desktop and other software, but considered Acorn's ARM3 products, alongside competition based on the 80486, SPARC and 88000 processors, to be more capable of such tasks.

Although there were expectations that Acorn's corporate parent, Olivetti, might have provided opportunities for ARM-based Unix workstation products, leveraging its relationship with AT&T as the proprietor of Unix, it became apparent that AT&T's own interests lay with products based on the SPARC architecture,[51] with AT&T also having an ownership stake in Sun.

[64] In 1994, the Risc PC launched with an improved chipset that was amenable to running Unix, and amidst a certain level of interest in the "large potential" of Unix running on the new machine,[65] the independent RiscBSD initiative was announced in August 1994 to bring "a base of BSD4.4 - probably the NetBSD flavour" to this hardware platform.

[66] A "very, very alpha kernel" was demonstrated after six weeks of initial effort by the RiscBSD developers at the Acorn World show in late 1994.

Meanwhile, another initiative, ArcBSD, sought to port FreeBSD to "all 32-bit Acorn machines with sufficient RAM and hard disk space".