ARM To Move to 64bit with ARMv8

Big news from ARM over the past few days. The processor architecture, once strictly an embedded affair for low-power devices, is going big. Not only has ARM announced it’s going 64bit, HP has announced it’s going to build servers with ARM processors. It seems all the pieces are now in place for ARM.

The 64bit announcement is a pretty big one – as far as I know, all other somewhat relevant processor architectures have long since made the switch to 64bit, leaving only ARM as 32bit. Of course, with its main focus on embedded devices, the switch to 64bit wasn’t as high a priority as with other instruction sets. However, now that ARM wants to move beyond all that, and now that it wants to run Windows, the time to go 64bit has arrived.

ARMv8, as it’s called, obviously builds on what came before, but it also adds, for the first time, 64bit processing. ARMv8 consists of two main execution states, AArch64 and AArch32. AArch64 introduces the new 64bit instruction set, while AArch32 is the continuation of the current ARMv7 architecture.

“With our increasingly connected world, the market for 32-bit processing continues to expand and evolve creating new opportunities for 32-bit ARMv7 based processors in embedded, real-time and open application platforms,” ARM CTO Mike Muller said, “We believe the ARMv8 architecture is ideally suited to enable the ARM partnership to continue to grow in 32-bit application spaces and bring diverse, innovative and energy-efficient solutions to 64-bit processing markets.”

Whenever someone introduces a major new revision of an instruction set, I usually turn to Ars Technica’s Jon ‘Hannibal’ Stokes, currently writing for Wired (owned by the same company which owns Ars) on a more occasional basis (at least, that’s how I understand it). His conclusion is that ARM’s 64bit extensions are purely about increasing the size of addressable memory, and not about performance per se. In addition, the increase in register size will negatively affect power usage.

“ARM’s 64-bit parts will pay a price in power efficiency for the boost to memory capacity and forward compatibility,” Stokes states, “The wider register file uses more logic and power on the die, and the wider integers and addresses will increase internal and external bus traffic. At the level of a desktop or server microprocessor, the power cost of these two items will be completely negligible. But in the sub-milliwatt regime where many of ARM’s mobile chips operate, there would be no reason to pay a power penalty for an increased memory capacity that won’t be used anyway.”

Interestingly enough, it seems the talks between Microsoft and ARM about bringing Windows NT to ARM was one of the driving forces behind the move to 64bit. As such, Microsoft made an appearance in ARM’s press release. “ARM is an important partner for Microsoft,” said KD Hallman, a general manager at Microsoft, “The evolution of ARM to support a 64-bit architecture is a significant development for ARM and for the ARM ecosystem. We look forward to witnessing this technology’s potential to enhance future ARM-based solutions.”

In the meantime, HP is (as far as I can recall) the first major OEM to build ARM-based servers – if the reports by The Wall Street Journal and Bloomberg are correct. HP’s going to cooperate with chip start-up Calxeda. In other words, HP has decided to work with a relatively unknown chip maker, instead of one of the more established names. Calxeda is, however, partly owned by ARM itself, so in essence, ARM and HP are working together pretty closely on this one.

Intel is of course not happy with this, since this is basically HP and ARM directly attacking Intel’s bred and butter. “We don’t take any threats to our server business lightly, but there are number of challenges for the ARM architecture to be successful in the server market,” Intel spokesman Bill Calder told the WSJ, “We believe the best-performing platform will win.” AMD didn’t comment.

Like I said in the introduction, all the pieces are now in place for ARM. They flat-out own the mobile space pretty much uncontested, and they’re now moving to servers -I’m sure other form factors, like desktops and laptops, are next.


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