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Why the ARM architecture is shaped the way it is
Peter Clarke
11/26/2012 02:25 PM EST   35 comments


It is arguable that ARM and Intel, the two companies locked in head-to-head processor competition, represent two different poles and philosophies.

ARM is modestly British while Intel is brashly American. Intel's chips have been dominant in personal computers for decades while ARM's architecture has been market leader in cellphones and smartphones. ARM is skilled at low power and power efficiency and is trying to move up to higher performance. Intel has always pursued performance but is now working to offer low power versions of its microprocessors. Intel is an integrated device maker. ARM does not even sell chips but licenses out its processor architecture and circuit designs to semiconductor partners.

To understand why the ARM architecture and culture is shaped the way it is and is different to processor trailblazer Intel, let's go back to a time before the formation of ARM; to Cambridge, England in the mid-to-late 1970s, in the early days of EE Times.

Sophie Wilson is now engineering director and distinguished engineer at Broadcom but back in the 1970s Roger Wilson was a mathematics undergraduate with a strong interest in computing.

Wilson had joined the university's computer and microprocessor societies, student-run interest groups that held regular meetings and, in the case of the microprocessor society, produced a magazine.

"One of the articles I contributed was on low power but it was not my only area of interest," Wilson told EE Times.

However, Hermann Hauser, a Cambridge physics alumni, who was thinking what to do next in his career had the idea of creating an electronic pocket diary. Obviously, that would need to be battery operated and low power. He therefore asked around trying to find out who at the university might be able to design such a thing for him and Wilson remembers being approached after a university lecture by contacts of Hauser's.

Wilson had memorized the RCA CMOS logic handbook of 1972 at a time when most ICs were not made using CMOS. Initially CMOS logic was slower than TTL. However, because the logic thresholds of CMOS were proportional to the power supply voltage, CMOS devices were well-adapted to battery-operated systems with simple power supplies, in which the voltage might vary. "CMOS was graduating from 15-volts to 5-volts," recalls Wilson, which provided further power saving opportunities.

The result was that when Hauser asked whether Wilson could design such a low-power system the second-year undergraduate student simply said "yes!"


Click on image to enlarge.

Sophie Wilson

Wilson started doing designs without any form of contract, just because that is what members of the computer and microprocessor societies liked to do. Each had their own favorite microprocessors and at this stage in the 8-bit era there were choices. Wilson had experience of designing around the 6502, including an early form of embedded system; an electronically controlled cow feeder for a firm in Harrogate.

The 6502 was designed by Chuck Peddle and Bill Mensch for MOS Technology Inc. in 1975 and when it was introduced was considerably lower cost than equivalents from Intel and Motorola. Mensch went on to form Western Design Center Inc. (Mesa, Arizona) which made the 65C02, the CMOS version of the processor.

At about the same time another Cambridge undergraduate was working for Science of Cambridge Ltd. on the Microcomputer Kit 14 (MK14) home-build computer, first introduced in 1977.

Science of Cambridge was one of the companies operated by Clive Sinclair (now Sir Clive Sinclair) whose Sinclair Radionics company had enjoyed mixed success in the UK supplying hi-fi audio electronics, and some of the earliest pocket calculators. The MK14 was based on a National Semiconductor 8-bit processor and the undergraduate was Steve Furber, now Professor Steve Furber of Manchester University.

Wilson remembers that it was while discussing plans for the electronic pocket diary Hauser pointed to other plans at the back of the sheaf of papers. These were Wilson's own plans for a personal computer. "At the microprocessor society we all had our own designs," Wilson recalls.

Wilson remembers that at this time the MK14 was starting to get press coverage and it seemed like personal computers might be about to take off. Hauser asked if Wilson's personal computer design would work. Wilson simply said "yes." That was that design that went on to form the Acorn System 1 personal computer based on the 6502.


Click on image to enlarge.

From tiny Acorns: Front board of an Acorn System 1
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przemek0
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re: Why the ARM architecture is shaped the way it is
przemek0   4/22/2013 9:19:57 PM
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Shrug---it's more complicated than that, my dear Atlas. If you squint at published benchmarks like Specmark just right, the more complex ARM models gets comparable or better performance per GHz. The real reason why x86 architecture runs your favourite applications is, as you pointed out, because they are not available for ARM, because Wintel. This is changing slowly: there are reports that PC sales are crashing, and the Wintel shiny front wall starts showing cracks. Will SolidWorks be available and usable on Android any time soon? Probably not, but the reason is not 'more transistors' or better architecture on x86.

CC VanDorne
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re: Why the ARM architecture is shaped the way it is
CC VanDorne   2/12/2013 4:43:25 PM
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What an odd reply! I think the point is that this is story about people, and at some point in the timeline the main character in the story had a sex-change, which is a remarkable thing, making it a glaring omission from the story.

CC VanDorne
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re: Why the ARM architecture is shaped the way it is
CC VanDorne   2/11/2013 8:17:26 PM
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No more caffine for you, Overcamp!

Greg.Overkamp
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re: Why the ARM architecture is shaped the way it is
Greg.Overkamp   12/27/2012 5:48:53 PM
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Nobody gives rat's ass what you used registers for on any CPU. ARMH is successful because customers can design targeted SOCs in 1/4 the time it take Intel to provide a reference design for what they define as the next mobile CPU one year too late.

Greg.Overkamp
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re: Why the ARM architecture is shaped the way it is
Greg.Overkamp   12/27/2012 5:42:51 PM
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agk I have read your comments numerous times and they are an uninspired wasted of time and space for the informed. Please go away.

Peter Clarke
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re: Why the ARM architecture is shaped the way it is
Peter Clarke   12/7/2012 7:55:07 PM
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@richyoung I understand the Duchess of Cambridge was caught topless by a long lens photographer, but I also understand it was without her knowledge and that it was published against her wishes.

richyoung
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re: Why the ARM architecture is shaped the way it is
richyoung   12/7/2012 6:14:29 PM
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Most processors at the time of the 68000 were CISC or multiple clocks per instruction. It wasn't until later when power and size for embedded applications were the drivers that brought RISC (ARM) type processor to the forefront.

richyoung
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re: Why the ARM architecture is shaped the way it is
richyoung   12/7/2012 6:08:12 PM
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Modestly British? Brashly American? Wasn't the future queen topless on the front of the newspaper a few weeks back?

ddaly
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re: Why the ARM architecture is shaped the way it is
ddaly   12/7/2012 2:03:56 PM
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This is more a *very* brief history of the people responsible for the design of the ARM architecture than it is a history of the conception of the design itself. I walk away from reading this article wanting to know way more about the design philosophy and design choices that were made regarding how the architecture came together. To me, the instruction set and the programmer's model, and the thought process going into their design, constitute much of what I would consider the "shaping" of the architecture. That merited one short paragraph. That the ARM architecture had to be simple, compact, fast, and have low power consumption is a little obvious. That the framers of the ARM architecture have their roots in the 6502 is little more than interesting trivia.

Peter Clarke
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re: Why the ARM architecture is shaped the way it is
Peter Clarke   12/7/2012 12:49:04 PM
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@Johnswolter Glad you found the other pages. Thanks for pulling me up on the 80286 error. I will correct.

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