ARM Readies Cores For 64-Bit Computing

snydeq writes "ARM Holdings will unveil new plans for processing cores that support 64-bit computing within the next few weeks, and has already shown samples at private viewings, InfoWorld reports. ARM's move to put out a 64-bit processing core will give its partners more options to design products for more markets, including servers, the source said. The next ARM Cortex processor to be unveiled will support 64-bit computing. An announcement of the processor could come as early as next week, and may provide further evidence of a collision course with Intel."

Comments

Re:What's the point?

[TheRaven64]

Look at Linux benchmarks for 32 vs 64-bit filesystem and OpenSSH performance

What benchmarks are you looking at? If you're comparing x86 to x86-64, then you are going to get some very misleading numbers. In addition to the increased address space, x86-64 gives:

• A lot more registers (if you're doing 64-bit operations, x86-32 only has two usable registers, meaning a load and a store practically every other instruction).
• The guarantee of SSE, meaning you don't need to use (slow) x87 instructions for floating point.
• Addressing modes that make position-independent code (i.e. anything in a .so under Linux) much faster.
• Shorter instruction sequences for some common instructions, replacing some short-but-rarely-used sequences.

Offsetting this is the fact that all pointers are now twice as big, which means that you use more instruction cache. On a more sane architecture, such as SPARC, PowerPC, or MIPS, you get none of these advantages (or, rather, removal of disadvantages), so 64-bit code generally runs slightly slower. The only reason to compile in 64-bit mode on these architectures is if you want more than 4GB of virtual address space in a process.

The ARM Cortex A15 supports 40-bit physical addresses, allowing up to 1TB of physical memory to be addressed. Probably not going to be enough for everyone forever, but definitely a lot more than you'll find in a typical server for the next couple of years. It only supports 32-bit virtual addresses, so you are limited to 4GB per process, but that's not a serious limitation for most people.

ARM already has 16 GPRs, so you can use them in pairs and have 8 registers for 64-bit operations. Not quite as many as x86-64, but four times as many as x86, so even that isn't much of an advantage. All of the other advantages that x86-64 has over x86, ARM has already.