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Bringing the first native OS for Arm back from the brink

Steve Revill of RISC OS Open chats to us about taking the project into the future

Retro Tech Week The mid-1980s codebase for RISC OS, the original native OS for the Arm processor, is still run on present-day hardware and actively maintained and developed. We spoke to RISC OS Open boss Steve Revill about its 26-bit origins, working to bring it to newer 32-bit Arm chips, efforts to update its BSD-based network stack, and more.

RISC OS Open is the company that steered RISC OS to modern Arm chips for Castle Technology's Iyonix and other hardware.

RISC OS was created at Acorn, the British company that in 1981 released the BBC Micro. Although Acorn never quite cracked the US market and its machines are little known outside Europe, the BBC Micro was a highly influential machine. The team that designed it went on to create the Arm processor among other things.

An early form of the OS codenamed Arthur – short for A RISC by THURsday – appeared on the world's first Arm-powered computer, the Acorn Archimedes, back in 1987. Updated and renamed to RISC OS with version 2, it narrowly managed to survive Acorn, and despite some disputes it's still around. In 2018, it was officially open sourced.

As we noted last year, the only other OS from that period that's still around today, NeXTstep descendant Apple macOS, now also runs on Arm hardware: the M1 and M2 Macs.

While macOS is a Unix, an OS with its roots in the 1960s, RISC OS is something else: its core is hand-coded in assembler, it's tiny and very fast at what it does, and it still only supports its original processor architecture – but today, that's the most widely used CPU architecture in the world. ®

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