The Design that Made ARM

By Cadence

November 25, 2015

I sat down with Simon Segars, the CEO of ARM last Friday. As I said yesterday, it is ARM's 25th birthday this week, on Friday if you want the precise date. Although today, of course, we think of even the largest ARM processors as something to embed in an SoC, when the first ARMs were created they were standalone processors taking up the whole die. The ARM1 and ARM2 were just processors. With the ARM3, there was room for a cache. By the time ARM was spun out of Acorn, they were working on the ARM6, a processor and cache, intended for the Apple Newton. Unfortunately the Newton was way ahead of its time and was not a commercial success.

The turning point for ARM was the ARM7. Actually the ARM7TDMI. What do all those letters mean? D was for debug, allowing for JTAG-based debugging. M was for multiplier, it had a fast hardware multiplier. I was for Icebreaker, a sort of on-chip in-circuit-emulator that allowed for hardware breakpoints and watchpoints. But the most important letter was the T that stood for Thumb.

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