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I believe the question is more to do with the hardware options. Going to 64-bit will require a great deal more silicon area with a consequent increase in power

I believe the question is more to do with the hardware options. Going to 64-bit will require a great deal more silicon area with a consequent increase in power consumption, which tends to go against the ARM philosophy (indeed, the later ARM instruction sets have gone more in the direction of 16bit).

rbanffy 17y ago
There is no real need to migrate to 64-bit unless you need to cleanly address more than 4 GB of memory. The case for the x86 migration to 64-bits was not so much the extra memory space, but the extra registers. ARM always had plenty of them. More to the point, moving ARM to 64-bits is relatively simple - and the ARM cores are so small even if you had twice the silicon area for that (a worse than worst-case-scenario) you would end up with a core that is still a fraction the size of a tiny x86. A Cortex core occupies less than 2 square millimeters. With cache.
- timthorn 17y ago
  Ah, Cortex ... Cortex is the branding for the ARM implementations of the ARM v7 Architecture. A brand was chosen for the first time because historically, even numbered ARM cores don't sell well (ARM8, anyone? ARM10?), so the next core after the ARM11 would have had to skip to ARM13. But 13 is unlucky. So that's ARM15 then... In addition, it would be very easy for the ARM v7 architecture to be confusd with the ARM7TDMI implementation of the ARM v4 architecture. The grand plan was to bring out new cores in V7 targetting three distinct market segments - Applications, Realtime and Microcontrollers (see what they did there?!), with very different performance points and feature sets. Thus, the Cortex M3 has a die size of 0.86mm2 on a 180nm process, but that's a weedy core. The A8 has a die size of a bit under 4mm2 on a 65nm (albeit speed optimised) process, without the ETM included. So, I'm not quite sure what core you are talking about - but it is also the case that the Atom die does contain a significant number of perhiperals and busses. A 64-bit ARM won't have a problem beating an x64 processor in terms of MIPS/Watt, I'm fairly sure. Edit - I should have explained that the number following the A/R/M is meant to indicate performance and not be a version number. The A5 and A9 both came out after the A8, for example - the ARM market isn't about increasing performance with every design, but ensuring a good fit for a design envelope.
  - rbanffy 17y ago
    "So, I'm not quite sure what core you are talking about" http://www.arm.com/products/CPUs/ARM_Cortex-R4F.html http://www.arm.com/products/CPUs/ARM_Cortex-R4F.html Whatever that is. I am no ARM expert. Edit: I think this one would be better. The R is for real-time applications http://www.arm.com/products/CPUs/ARMCortex-A9_MPCore.html http://www.arm.com/products/CPUs/ARMCortex-A9_MPCore.html This other one (http://www.arm.com/products/CPUs/ARM_Cortex-A8.html http://www.arm.com/products/CPUs/ARM_Cortex-A8.html) is about 4 mm2.

rbanffy 17y ago

There is no real need to migrate to 64-bit unless you need to cleanly address more than 4 GB of memory. The case for the x86 migration to 64-bits was not so much the extra memory space, but the extra registers. ARM always had plenty of them. More to the point, moving ARM to 64-bits is relatively simple - and the ARM cores are so small even if you had twice the silicon area for that (a worse than worst-case-scenario) you would end up with a core that is still a fraction the size of a tiny x86. A Cortex core occupies less than 2 square millimeters. With cache.

timthorn 17y ago
Ah, Cortex ... Cortex is the branding for the ARM implementations of the ARM v7 Architecture. A brand was chosen for the first time because historically, even numbered ARM cores don't sell well (ARM8, anyone? ARM10?), so the next core after the ARM11 would have had to skip to ARM13. But 13 is unlucky. So that's ARM15 then... In addition, it would be very easy for the ARM v7 architecture to be confusd with the ARM7TDMI implementation of the ARM v4 architecture. The grand plan was to bring out new cores in V7 targetting three distinct market segments - Applications, Realtime and Microcontrollers (see what they did there?!), with very different performance points and feature sets. Thus, the Cortex M3 has a die size of 0.86mm2 on a 180nm process, but that's a weedy core. The A8 has a die size of a bit under 4mm2 on a 65nm (albeit speed optimised) process, without the ETM included. So, I'm not quite sure what core you are talking about - but it is also the case that the Atom die does contain a significant number of perhiperals and busses. A 64-bit ARM won't have a problem beating an x64 processor in terms of MIPS/Watt, I'm fairly sure. Edit - I should have explained that the number following the A/R/M is meant to indicate performance and not be a version number. The A5 and A9 both came out after the A8, for example - the ARM market isn't about increasing performance with every design, but ensuring a good fit for a design envelope.
- rbanffy 17y ago
  "So, I'm not quite sure what core you are talking about" http://www.arm.com/products/CPUs/ARM_Cortex-R4F.html http://www.arm.com/products/CPUs/ARM_Cortex-R4F.html Whatever that is. I am no ARM expert. Edit: I think this one would be better. The R is for real-time applications http://www.arm.com/products/CPUs/ARMCortex-A9_MPCore.html http://www.arm.com/products/CPUs/ARMCortex-A9_MPCore.html This other one (http://www.arm.com/products/CPUs/ARM_Cortex-A8.html http://www.arm.com/products/CPUs/ARM_Cortex-A8.html) is about 4 mm2.