Via Dave Moore on the bbc-micro list:

"here's a video of the Steve Furber talk, which was kindly filmed by Jason Fitzpatrick of The Centre for Computing History:"

http://www.computinghistory.org.uk/det/ ... 3-09-2009/

About 35 minutes in, Steve mentions the trip that he and Sophie Wilson made to WDC - the 65816 was built into one of Acorn's products but they had decided to make their own processor to succeed the 6502 (which was ARM of course)

Running Time : 1hr 8 mins

"A presentation made at Acorn World - 2009-09-13 by Professor Stephen Furber CBE. He talks about his involvement with the Mk14, SC/MP controlled fruit machines, the design of the BBC Micro, the development of the ARM processor and his latest project : SpiNNaker."

ACM Queue has an interview with Steve Furber about ARM and low-power computing - of course, he mentions the 6502 in the BBC micro, and what processor to move to next.

Rather than butchering a long quote, I'll paraphrase: they'd tried various 16-bit processors and found them wanting on two counts.

First, they had complex instruction sets, therefore poor interrupt response. The BBC Micro had no DMA, and needed fast interrupts for realtime I/O. They found the 16bit micros of the early 80's "had worse interrupt response time than the 6502"

Second, their models told them performance depended principally on usable memory bandwidth. Cache memories were "not commonplace, so the available memory bandwidth was determined by the performance of commodity DRAM." And yet, the processors they looked at couldn't saturate DRAM bandwidth. They felt that was "the wrong answer. The memory bandwidth was the primary resource, and it was the processor's job to make the maximum possible use of that. "

Then they "got wind of the RISC papers published by Berkeley and Stanford"

At the risk of redundancy, I'd like to link to some threads over on StarDot with interesting connections to Steve Furber:

Some interesting Steve Furber observations
Interesting interview of Steve Furber (Acorn era)
Steve Furber at VCF 2013 - Transcript