Clearing up questions about 64-bit ARM processors

Emerging 64-bit ARM processors are headed to the data center and may enable a new wave of scalable, energy-efficient enterprise-class computing.

Will the drive for low power bring 64-bit ARM processors permanently into the data center, or are they destined for non-enterprise applications?

Reduced instruction set computing (RISC) revolutionized the design of electronic devices. Rather than using a generic microprocessor based on conventional complex instruction set computing (CISC), RISC provides a simpler processing engine. By stripping out unneeded instructions and optimizing pathways, RISC processors provide outstanding performance at a fraction of the power demand of CISC devices. However, RISC processor use has been largely limited to specialized devices such as printers, routers or cell phones. Only recently have RISC processors appeared in servers, so let's look at some issues involved in enterprise-class adoption of advanced RISC machines.

How will ARM processors handle 64-bit enterprise-class operating systems and applications? Isn't ARM limited to 32-bit systems?

Traditional advanced RISC machine (ARM) processors are based on the 32-bit, AArch32 designs developed back in the 1980s by ARM Holdings in the UK. ARM Holdings does not manufacture ARM chips. Instead, the design is licensed to independent chip makers that can customize and manufacture the design for specific purposes. This paradigm slowed the development of ARM processors compared to proprietary developers, like Intel or AMD. Organizations moving to 64-bit operating systems have largely held off on deploying ARM-based servers to avoid making 32-bit hardware investments.

However, 64-bit ARM chips are coming. Back in 2011, ARM Holdings developed a 64-bit (AArch64) architecture along with a new instruction set dubbed A64. Major chipmakers have licensed the design and will be rolling out their individual adaptations of the processor in the next few years. For example, AMD expects to release an ARM-based Opteron in 2014.

There is also some support for operating systems like Linux, and 64-bit ARM support is already present in Linux kernel 3.7. Support for other operating systems is also expected to become available as actual ARM products get closer to the market.

Who will be developing 64-bit ARM processors and systems? What will 64-bit ARM servers look like? What are the best workloads for an ARM server?

The reference design for the 64-bit ARM processors -- such as the Coretex-A50 series -- is already complete and is currently licensed by major chipmakers including Applied Micro Circuits Corporation, Advanced Micro Devices (AMD), Broadcom, Calxeda, Samsung and ST Microelectronics. However, since ARM Holdings does not make the chips it designs, it will be up to the individual licensees to modify, debug, evaluate and manufacture devices based on the underlying reference design. This means it may take several years before 64-bit ARM chips are broadly available for integration into server boxes.

Also, remember that 64-bit ARM processors will not use conventional server architectures. ARM chips cannot outperform their CISC counterparts -- such as conventional Xeon or Opteron chips -- on an individual basis, so ARM-based servers are unlikely to resemble CISC servers. Instead, the value proposition behind ARM is high processing scalability with low power use, so expect to see enterprise-class ARM-based servers -- such as Dell's Zinc, HP's Moonshot or Penguin's UDX1 servers – to appear, with hundreds of ARM processors where each processor contains multiple cores. As an example, Calxeda is reported to be developing a 480-core ARM server based on 120 quad-core 32-bit ARM processors; 64-bit ARM servers would likely follow a similar strategy of high scalability.

Not every workload is suited for ARM servers. In general, workloads that have low processor utilization on standard CPUs, small memory requirements, small computing needs for each thread and the ability to scale using multiple processors are the best candidates for ARM servers. These often include applications like Web hosting, Hadoop and other Java-based applications. Organizations that are new to ARM platforms should make the investment in proof-of-principle projects to verify the suitable performance characteristics of workloads running on ARM boxes before putting such products into production.

Will 64-bit ARM processors support virtualization? What other features or capabilities will next-generation ARM processors include?

Yes, 64-bit ARM processors will support virtualization through the inclusion of virtualization extensions -- similar in principle to Intel-VT and AMD-V virtualization extensions present in Intel and AMD server processors -- and support for large physical address extensions.

Beyond the shift to a 64-bit data/address bus and a redesign of the 32-bit (A32) command set, AArch64 chips provide advanced digital signal processing (DSP) capabilities that enable high-performance media processing, along with AES, SHA-1 and SHA-256 cryptography and TrustZone technology designed to create trusted execution environments that secure high-performance computing platforms against software attacks.

IT professionals are slowly learning the lesson that electronics manufacturers have known for decades -- you can't always get the most efficient results by throwing a CISC processor at every computing problem. ARM processors provide performance and energy efficiency, along with processing scalability. Although ARM may not be right for every computing workload, the appearance of 64-bit ARM chips may finally put a spotlight on ARM-based computing in the data center.

This was first published in January 2013

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