This is a collection of information about Acorn’s RISC iX Operating System, and the hardware it runs on (e.g. R140, R225, R260). Unfortunately reliable information about RISCiX is hard to find nowadays. Acorn withdrew support at the end of1992. I have gleaned the information from the Acorn RISCiX manuals,  the C.S.A newsgroups and other publications. I was going to produce it as a RISCiX FAQ but this seems a better idea.

 RISCiX is Acorn's version of Unix. Unlike Arthur and RISC OS, RISC iX was a true multitasking operating system. RISC iX was released by Acorn in 1988. To quote from the R140 Operations Guide "RISC iX is Acorn's version of Berkeley 4.3BSD UNIX with enhancements including NFS (Network File System) and the X Window System". Specifically it contains Sun NFS version 3.2, and X11 Window System release 2. This means that Acorn were probably paying royalties for some components of RISC iX, and possibly explains why some people believe RISC iX was licensed from Sun.

In more detail the RISC iX User Guide says:
"RISC iX is a port to the ARM processor of the Berkeley 4.3 UNIX operating system (4.3BSD) with SVID extensions, Network File System (NFS) software, the X Window System and window managers.

Here is a general list of the software supplied:

I have found reference to several different versions of RISCiX. There were 2 major RISC iX releases 1.1x and 1.2x. The versions were:

RISC iX VersionNotes
1.13Release with R140 January1989
1.2Released with R260 June 1990
1.21cIncludes Ether3 support

RISC iX 1.2x was significantly enhanced and had more features than v1.1x. In particular it was certified to X/Open's XPG3 Base profile. It also contained X11 Window System release 4, X.desktop and Motif. Here is the Acorn Application note RISC iX 1.2 Upgrade Products .

RISC iX hardware

Details of the Acorn computers which run RISC iX are available HERE


RISC iX was designed to run on computers with an ARM2 CPU (R140) and can also run on an ARM3 CPU (R225 & R260). RISC iX does not support later CPUs (e.g. ARM6, ARM7 or StrongARM), so you cannot run RISC iX on RiscPC s or other more modern Acorn computers.
RISC iX will in fact run on any Acorn hardware that meets the requirements listed here, so you can run it on a suitably upgraded A310 or even an A3000.


 RISCiX requires a mimimum of 4 MB but is happier with 8MB or more. An R140 has 4MB, and R260 can have upto 16MB.

 Podule Backplane

 The early Archimedes backplanes did not allow interupt masking. A special backplane was produced for the R140 to enable interupt masking (later backplanes did not have this limitation). On RISC iX machines, hardware on the podule backplane allows IRQs from individual cards to be masked and tested for, which allows podules to have interrupts with different priorities. If, at boot time, RISC iX cannot find the backplane interrupt masking hardware it will print a warning and then handle all interrupts at the lowest priority requested. This will adversely affect performance.

 Hard disc controllers and SCSI Cards

 RISC iX only supports the on board ST506 disc controller, the AKD52 Winchester podule and the Acorn SCSI podule. It does not support non-Acorn SCSI cards or any IDE controllers. Any drivers that do exist for A5000 IDE, Atomwide Ether3 or other hardware are betas and not necessarily reliable. This means that RISC iX will not run on A5000 or subsequent Acorn computers. The reason for this is that RISC iX uses its own drivers (not the RISC OS drivers) and drivers for other interfaces do not exist in the kernel.
There is no support for CDROMs in RISC iX

Disc partitions

RISC iX has its own filesystem type (4.3 - from BSD 4.3?) which is completely different to the RISC OS filecore. Before installing RISC iX you need to partition the hard disc. The R140 and R260 came with the hard disc partitioned into a small (minimal) RISC OS partion for the bootloader and a large RISC iX partition.

 If you are using a SCSI disc then you partition it with Acorns's SCSIDM utility which asks you if you want to create a RISC iX partition. It prompts you for the different filesystems you want to create ( the minimum is swap and root (/). If you have an ST506 disc, I think there was a version of !HFORM which allowed you to partition the disc.

Network Interface (Ethernet)

RISC iX only supports the Acorn AKA25 Ethernet cards. it supports Ether1 and Ether2 cards and may support Ether3.

Network Interface (Econet)

RISC iX supports Econet. If an Econet interface is fitting, it can be configured in RISC iX and used to network with other systems on an Econet network. It will also support IP over Econet.


Legal versions of RISC iX either came pre-installed on a R140 or R260, or were installed by Granada Microcare. Acorn did not supply distribution media to customers ( although in 2006 a set of 14 floppy discs with an installable copy of RISC iX 1.14 were sold on ebay). If you ordered RISC iX, Grenada Microcare would make an appointment, come along and install it from a tape drive, taking the tape away afterwards.

You could create a minimal install for RISC iX 1.1x on 3 floppies (boot, kernel and archive) by running a supplied script. These floppies could then be used to build a minimal RISC iX system, to allow you to restore from a backup tar. Obviously you were expected to take regular backups of the system for this to work! Here is the Grenada Readme about creating and using the recovery floppies.
I am told this only worked with RISCiX 1.1x, because the 1.2x kernel was too big, even when compressed, to fit on a floppy disc.
The other route was to clone your SCSI disc to a second SCSI disc, which then provided a backup that could simply replace the failed disc. James Carter has documented this Cloning a RISC iX disc

RISC iX 1.1x

RISC iX v 1.1x ran on the R140 which is based on the A440, with ARM2 and 56MB ST506 hard disc drive. The R140 came with RISC OS 2 in ROM. RISC OS was only used to boot the computer and then automatically (could be set to manual) booted RISC iX at which point RISC OS was lost. RISC iX v1.1x required an ST506 hard disc to boot from. An A440 with 4 MB memory and a suitable sized disc could also have RISC iX installed on it..


The RISC iX 1.1x manuals are:

RISC iX 1.2x

RISC iX v1.2x ran on the R260 (and R225) which is based on the A540, with ARM3, an AKA30 SCSI card and a 100MB SCSI hard drive. The R260 came with RISC OS 2.01 in ROM which was a modified version of RISC OS 2 and included the RISCiXFS module. The R260 booted in the same ways as the R140, via RISC OS. An A540 could have RISC iX installed on it.


RISC iX Programmer's Reference Manual

There is a 2 volume RISC iX PRM:


!RISCiX, the RISC iX startup, was written for RISC OS 2.01. If you try to boot RISC iX under RISC OS 3.xx, it will fail with the message "panic: unknown hardware". If this happens run the patch supplied with RISC OS 3 for RISCiXFS which is on the RISC OS 3 Support Disc .

It is possible to configure !RISCiXFS so that RISC iX is not automatically booted (set *Configure no RISCOS off). If you do that you can run RISC OS as normal, subject the any limitations on disc size. You can run one or the other but not both at the same time. You cannot run RISC OS applications under RISC iX, or vice versa. However you can run a limited subset of RISCiX commands from RISC OS using the RISCiXFS module and allows you to:

Where to find software for RISC iX now

The old Acorn FTP site is preserved by RISCOS Ltd. There is a RISC iX section with a number of programs ported by Acorn to RISC iX. In fact this is the only source of RISC iX software that I have found. Available software packages include: