ARM is Already Considering 128-bit Mobile CPU
2014 looks to be an exciting year for mobile technology.
Earlier this year, Apple made headlines with its 64-bit SoC for the iPhone 5S. That SoC is now present in the iPad Air and the new iPad Mini Retina. Since the launch of the iPhone 5S, we've been hearing talk of a 64-bit Exynos from Samsung. Now ARM has confirmed that the chip is coming. The Korea Herald cites a senior manager at ARM as saying executives from Samsung and ARM met this week and discussed the ARM 64-bit chip expected to be used in a Samsung device next year.
Though it's not an official confirmation, rumors of a 64-bit Samsung device have been doing the rounds for a while. Word on the street is that the Galaxy S5 will include a 64-bit processor. No doubt if Samsung does include the 64-bit Exynos in the S5, we'll also see it in the next iteration of Galaxy Note as well.
Of course, with the rate at which mobile technology is evolving, it's hard to think about what's next without thinking about what's going to come in the future. To that end, it sounds like ARM is already considering a 128-bit processor. According to the KoreaTimes' ARM official, such a chip could hit the market in the next two years, but it's not set in stone.
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I'm guessing ARM's 128bits will be similar: provide more register bits to work with SIMD and add a subset of instructions that can actually work with 128bits values.
I'm guessing ARM's 128bits will be similar: provide more register bits to work with SIMD and add a subset of instructions that can actually work with 128bits values.
That's most likely the case. Dynamically scheduled machines scale exponentially in power and transistor consumption due to the massive backend bus and common data bus. 128 bit GPRs and 128 bit EUs across the board would cause ARM processors to lose their market position as low power CPUs without offering any sort of advantage.
64bits is enough to address huge swaths of memory space, but 64bits isn't much data to be processed in one cycle.
The real question is how much of our current and near future algorithms could benefit from 128bit general int registers.
Not pointless but it does have somewhat limited use cases...
- cryptography
- arbitrary length bitfield manipulations
- arbitrary precision math: 75% fewer partial multiplications, half as many intermediate steps for most other operations
- memory copying: half as many load/store operations to copy a given amount of data
This is assuming we do not count SIMD as legit 128bitness. If we count SIMD then it becomes useful for tons of things like audio and image/video processing.
Let's say you had a 64bit program that performed image manipulation. The program itself was 10MB and it allocated 240MB of RAM for data to work with for a total of 250MB of RAM.
Now here's a question for every one on Tom's who continually posts that you need 4GB of RAM to make use of 64bit.
Do you think this program, only occupying 250MB of RAM, will not give you any advantage on a system with less then 4GB of RAM? Think very carefully about your answer. This should weed out the people who actually understand 64bit from those that don't.
the response is by Ian Drew,Chief Marketing Officer and EVP Business Development in ARM. Here's a spoiler:
"Did you hear the joke about the 128 bit processor? ..."
Just like how we dont call current intel chips 256 bit chips, even tho they have 256 bit floating point units. When someone says a 32 bit or 64 bit cpu, etc, they are usually talking about the address space, or the general purpose register size..
What they really mean....is adding in widening their floating point unit, which certainly isnt a bad thing. Its just very missleading to call it a 128 bit cpu.
Just like how we dont call current intel chips 256 bit chips, even tho they have 256 bit floating point units. When someone says a 32 bit or 64 bit cpu, etc, they are usually talking about the address space, or the general purpose register size..
What they really mean....is adding in widening their floating point unit, which certainly isnt a bad thing. Its just very missleading to call it a 128 bit cpu.
Let's say you had a 64bit program that performed image manipulation. The program itself was 10MB and it allocated 240MB of RAM for data to work with for a total of 250MB of RAM.
Now here's a question for every one on Tom's who continually posts that you need 4GB of RAM to make use of 64bit.
Do you think this program, only occupying 250MB of RAM, will not give you any advantage on a system with less then 4GB of RAM? Think very carefully about your answer. This should weed out the people who actually understand 64bit from those that don't.
I think you need to understand the architecture a bit better. The 10 Meg program and the 240 Meg alloc'd space are stored in different segments. The OS takes care of the program while the program takes care of the data. Ignoring a bunch of details, essentially the OS is only going to be storing offsets, not an entire 64 bit pointer and the offsets are shorter than 64 bits. The virtual address space uses some creative techniques to appear larger and segments the pieces for easy conversion. Thus your 64 bits aren't useful except for much except physical addresses.
Not pointless but it does have somewhat limited use cases...
- cryptography
- arbitrary length bitfield manipulations
- arbitrary precision math: 75% fewer partial multiplications, half as many intermediate steps for most other operations
- memory copying: half as many load/store operations to copy a given amount of data
This is assuming we do not count SIMD as legit 128bitness. If we count SIMD then it becomes useful for tons of things like audio and image/video processing.
I agree those are some corner cases where 128 bit is useful. But those are limited uses and I would argue a ALU capable of 256 bit or even 515 bit math might be more useful here. It would be interesting to see split implementations again where the ALU and MMU where different sizes.
My 2 cents
Now, I know there's more overhead for translating addresses, the higher you go, and allowing more RAM, but beyond that, that's about it.
Edit: read the comments. Ok, its been debunked. I'd like to point out though the comments seems to be geared toward the relevance of 128 versus 64 from a PC perspective, and not at all about how it would benefit the typical ARM media consumption device.