StrongARM

Lore & Background

According to Allen Baum, the StrongARM traces its history to attempts to make a low-power version of the DEC Alpha, which DEC's engineers quickly concluded was not possible. They then became interested in designs dedicated to low-power applications which led them to the ARM family. One of the only major users of the ARM for performance-related products at that time was Apple, whose Newton device was based on the ARM platform. DEC approached Apple wondering if they might be interested in a high-performance ARM, to which the Apple engineers replied 'Phhht, yeah. You can't do it, but, yeah, if you could we'd use it.'

The StrongARM was a collaborative project between DEC and Advanced RISC Machines to create a faster ARM microprocessor. It was designed to address the upper end of the low-power embedded market, where users needed more performance than the ARM could deliver while being able to accept more external support. Targets were devices such as newer personal digital assistants and set-top boxes. Traditionally, the semiconductor division of DEC was located in Massachusetts. In order to gain access to the design talent in Silicon Valley, DEC opened a design center in Palo Alto, California, led by Dan Dobberpuhl. Another design site in Austin, Texas was created by some ex-DEC designers returning from Apple Computer and Motorola. The project was set up in 1995, and quickly delivered their first design, the SA-110.

DEC agreed to sell StrongARM to Intel as part of a lawsuit settlement in 1997. Intel used the StrongARM to replace their ailing line of RISC processors, the i860 and i960. When the semiconductor division of DEC was sold to Intel, many engineers from the Palo Alto design group moved to SiByte, a start-up company designing MIPS system-on-a-chip (SoC) products for the networking market. The Austin design group spun off to become Alchemy Semiconductor, another start-up company designing MIPS SoCs for the hand-held market. A new StrongARM core was developed by Intel and introduced in 2000 as the XScale.

Reader's Guide

The StrongARM family is notable for being a high-performance implementation of the ARM v4 architecture developed by DEC, a company better known for its Alpha line. Its development was driven by the recognition that a low-power Alpha was infeasible, leading DEC to pursue a faster ARM. The SA-110, the first design, was delivered quickly after the project's 1995 setup and became the highest performing microprocessor for portable devices throughout 1996. Its first design win was the Apple MessagePad 2000, and it was also used in products such as the Acorn Computers Risc PC and the Eidos Optima video editing system.

The acquisition of StrongARM by Intel in 1997 as part of a lawsuit settlement allowed Intel to replace its struggling i860 and i960 RISC processors. Intel continued manufacturing the StrongARM and later introduced the XScale, a StrongARM-derived architecture, in the early 2000s. The SA-1100 and SA-1110 derivatives added integrated peripherals for portable applications, with the SA-1100 used in devices like the Psion netBook and Series 7. The SA-1110 was used in mobile phones and PDAs such as the Compaq iPAQ. The legacy of StrongARM includes its influence on Intel's mobile processor strategy and the spin-off of design teams that created MIPS-based SoC companies.

Did You Know?

• The SA-110 was the first microprocessor in the StrongARM family, announced on 5 February 1996.
• The SA-110 contained 2.5 million transistors and was fabricated in DEC's CMOS-6 process with a 0.35 μm feature size.
• The SA-110's lead designers were Daniel W. Dobberpuhl, Gregory W. Hoeppner, Liam Madden, and Richard T. Witek.
• The SA-1100 derivative reduced the data cache to 8 KB to accommodate integrated memory, PCMCIA, and LCD controllers.