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Why we don't have 128-bit CPUs (www.xda-developers.com)
submitted 2 years ago by to c/technology@lemmy.world
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[–] 129 points 2 years ago (5 children)

Is this a question?

We haven't even come close to exhausting 64-bit addresses yet. If you think the bit number makes things faster, it's technically the opposite.

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  • [–] 67 points 2 years ago (1 child)

    We don't even have true 64-bit addressing yet. x86-64 uses only 48 bits of a 64 bit address and 64-bit ARM can use anything between 40 and 52 depending on the specific configuration.

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  • [+] -66 points 2 years ago (3 children)
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  • [–] 36 points 2 years ago (1 child)

    I actually added detail that wasn't already discussed in the article?

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  • [–] 34 points 2 years ago (1 child)

    I actually didn’t know that about addressing before your comment and so I found it very interesting, thanks

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  • [–] 2 points 2 years ago

    Some applications use those unused bits to add tags to pointers but it's important to mask those out before attempting to dereference the address. I'm not sure about ARM but x86-64 requires bits 49-63 to be copies of bit 48 (kinda like sign-extension), ironically to ensure that no one is using those bits to store extra data.

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  • [+] 5 points 2 years ago (1 child)
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  • [+] -54 points 2 years ago (2 children)
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  • [–] 35 points 2 years ago (2 children)

    Yeah, 64 bit handles almost all use cases we have. Sometimes we want double the precision (a double) or length (a long), but we can do that without being 128-bit. It's harder to do half. Sure, it'd be slightly faster for some things, but it's not significant.

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  • [–] 22 points 2 years ago (1 child)

    And you can get 128-bit data to the CPU, so those things can be fast if we need them to be.

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  • [–] 21 points 2 years ago

    And we have wide instructions that can process this data, such as for multimedia applications.

    Addressing and memory size has been the historic motivator for wider registers, but it’s probably not going to be in my lifetime that I see the need for 128.

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  • [–] 9 points 2 years ago

    There's plenty of instructions for processing integers and fp numbers from 8 bits to 512 bits with a single instruction and register. There's been a lot of work in packed math instructions for neural network inference.

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  • [–] 34 points 2 years ago (1 child)

    Is this a question?

    For the people who don't know the answer? Yes.

    Not everything you see is intended for your consumption. Let people enjoy learning things.

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  • [–] 16 points 2 years ago* (1 child)

    I totally agree. I know a teacher who who likes to say:

    "I believe there really is no such thing as a dumb question. As long as it's an honest question (not rhetorical or sarcastic), then it's a genuine request for more information. So even if it's coming from a place of extreme ignorance, asking a question is an attempt to learn something, and the effort should be applauded."

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