Why we don't have 128-bit CPUs

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• just_another_person@lemmy.world ⁨4⁩ ⁨months⁩ ago

  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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  • jwr1@kbin.earth ⁨4⁩ ⁨months⁩ ago

    It's a link to an article I found interesting. It basically details why we're still using 64-bit CPUs, just as you mentioned.

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    • fmstrat@lemmy.nowsci.com ⁨4⁩ ⁨months⁩ ago

      Comment OP must never learn anything new. Good find.

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  • Technus@lemmy.zip ⁨4⁩ ⁨months⁩ ago

    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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    • just_another_person@lemmy.world ⁨4⁩ ⁨months⁩ ago

      [deleted]

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  • Voroxpete@sh.itjust.works ⁨4⁩ ⁨months⁩ ago

    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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    • Cocodapuf@lemmy.world ⁨4⁩ ⁨months⁩ ago

      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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  • Cethin@lemmy.zip ⁨4⁩ ⁨months⁩ ago

    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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    • sugar_in_your_tea@sh.itjust.works ⁨4⁩ ⁨months⁩ ago

      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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  • otp@sh.itjust.works ⁨4⁩ ⁨months⁩ ago

    Is this a question?

    Woah, meta.

    Yes, it is.

    This is not a question, though.

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• wewbull@feddit.uk ⁨4⁩ ⁨months⁩ ago

  We do, depending on how you count it.

  There’s two major widths in a processor. The data register width and the address bus width, but even that is not the whole story. If you go back to a processor like the 68000, the classic 16-bit processor, it has:

  • 32-bit data registers
  • 16- bit ALU
  • 16-bit data bus
  • 32-bit address registers
  • 24-bit address bus

  If you look at a Zen 4 core it has:

  • 64-bit data registers
  • 512-bit AVX data registers
  • 6 x 64-bit integer ALUs
  • 4 x 256-bit AVX ALUs
  • 2 x 128-bit data bus to DDR5 (dual edge 64-bit)
  • ~40-bits of addressable physical RAM

  So, what do you want to call this processor?

  64-bit (integer width), 128-bit (physical data bus width), 256-bit (widest ALU) or 512-bit (widest register width)?

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  • LeFantome@programming.dev ⁨4⁩ ⁨months⁩ ago

    I would say that you make a decent argument that the ALU has the strongest claim to the “bitness” of a CPU. In that way, we are already beyond 64 bit.

    For me though, what really defines a CPU is the software that runs natively. The Zen4 runs software written for the AMD64 family of processors. That is, it runs 64 bit software. This software will not run on the “32 bit” x86 processors that came before it ( like the K5, K6, and original Athlon ). If AMD released the AMD128 instruction set, it would not run on the Zen4 even though it may technically be enough hardware to do so.

    The Motorola 68000 only had a 16 but ALU but was able to run the same 32 bit software that ran in later Motorola processors that were truly 32 bit. Software written for the 68000 was essentially still native on processors sold as late as 2014 ( 35 years after the 68000 was released ). This was not some kid of compatibility mode, these processors were still using the same 32 bit ISA.

    The Linux kernel that runs on the Zen4 will also run on 64 bit machines made 20 years ago as they also support the amd64 / x86-64 ISA.

    Where the article is correct is that there does not seem to be much push to move on from 64 bit software. The Zen4 supports instructions to perform higher-bit operations but they are optional. Most applications do not use them, including the operating system. For the most part, the Zen4 runs the same software as the Opteron ( released in 2003 ). The same pre-compiled Linux distro will run on both.

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  • Blackmist@feddit.uk ⁨4⁩ ⁨months⁩ ago

    I gave up trying to figure out what the “bitness” of CPUs were around the time the Atari Jaguar came out and people described it as 64 bit because it had 32 bit graphics chip plus a 32 bit sound chip.

    It’s been mostly marketing bollocks since forever.

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    • SlothMama@lemmy.world ⁨4⁩ ⁨months⁩ ago

      The Jaguar lied with the truth, and I say this as someone who still owns one.

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  • Buffalox@lemmy.world ⁨4⁩ ⁨months⁩ ago

    At less than a tenth the size, this is actually a better explanation than the article.
    Also I agree that if you absolutely had to put a bit width on the Zen 4, the 2x128 bit data bus would probably be the best single measure.

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    • wewbull@feddit.uk ⁨4⁩ ⁨months⁩ ago

      Even then, at what point do you measure it? DDR interface is likely very much narrower than the interfaces between cache levels. Where does the core end and the memory begin?

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  • deddit@lemmy.world ⁨4⁩ ⁨months⁩ ago

    So, you’re saying it already goes to ‘11’?

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  • CetaceanNeeded@lemmy.world ⁨4⁩ ⁨months⁩ ago

    Not to mention most “8-bit” CPUs had a 16 bit address bus.

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    • wewbull@feddit.uk ⁨4⁩ ⁨months⁩ ago

      Yes, because 256 memory locations is a bit limiting.

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  • ZILtoid1991@lemmy.world ⁨4⁩ ⁨months⁩ ago

    Image With AMX, now we have 1024 bit processors!

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  • 9488fcea02a9@sh.itjust.works ⁨4⁩ ⁨months⁩ ago

    I’m surprised some marketing genius at the intel/amd hasnt started using the bigger numbers

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    • wewbull@feddit.uk ⁨4⁩ ⁨months⁩ ago

      I expect the engineers are telling the marketing people “No! You can’t do that. You’ll scare everyone that it’s incompatible.”

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  • ulterno@lemmy.kde.social ⁨4⁩ ⁨months⁩ ago

    I see it as the number of possible instructions.

    As in, 8 bit 8085 had 2^8^ possible instructions, 32 bit ones had 2^32^ and already had enough possible combinations that we couldn’t come up with enough functions to fill the provided space.

    CC BY-NC-SA

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    • wewbull@feddit.uk ⁨4⁩ ⁨months⁩ ago

      So “instruction encoding length”.

      I don’t think that works though. For something like RISC-V, RV64 has a maximum 32-bit instruction encoding. For x86-64 those original 8-bit intructions still exist, and take up a huge part of the encoding space, cutting the number of n-bit instructions to more like 2^(n-7)

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  • Cocodapuf@lemmy.world ⁨4⁩ ⁨months⁩ ago

    Very well said sir. I think you make your point quite effectively!

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• hades@lemm.ee ⁨4⁩ ⁨months⁩ ago

  We used to drive bicycles when we were children. Then we started driving cars. Bicycles have two wheels, cars have four. Eight wheels seems to be the logical next step, why don’t we drive eight-wheel vehicles?

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  • TonyTonyChopper@mander.xyz ⁨4⁩ ⁨months⁩ ago

    Lobbying by the auto corporations obviously. More wheels is more better

    Image

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    • CptEnder@lemmy.world ⁨4⁩ ⁨months⁩ ago

      So VM? Actually makes sense.

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    • VeganCheesecake@lemmy.blahaj.zone ⁨4⁩ ⁨months⁩ ago

      Huh, I’ve been in that train. Sudden, random hit of Nostalgia.

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  • kayazere@feddit.nl ⁨4⁩ ⁨months⁩ ago

    Funny how we are moving back to bicycles, as cars aren’t scalable solution.

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    • Surreal@programming.dev ⁨4⁩ ⁨months⁩ ago

      Bus is, though

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    • SaltySalamander@fedia.io ⁨4⁩ ⁨months⁩ ago

      But we aren't really.

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  • borari@lemmy.dbzer0.com ⁨4⁩ ⁨months⁩ ago

    Some of us drive 18-wheeled vehicles.

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    • IphtashuFitz@lemmy.world ⁨4⁩ ⁨months⁩ ago

      Some of us drive 48-wheeled vehicles.

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  • Liz@midwest.social ⁨4⁩ ⁨months⁩ ago

    See here’s where this analogy is perfect. Sometimes a bicycle is the best solution, just like how sometimes a microcontroller is the best solution. You use the tool you need for the job, and American product design is creating way too many “smart” products just like how American town planning demands too many cars. Bring back the microcontroller! Bring back the bike!

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  • randombullet@programming.dev ⁨4⁩ ⁨months⁩ ago

    I mean we do right?

    Trains are typically 2 x 4 bogies.

    But then high speed rail have fewer wheels due to friction.

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  • Fal@yiffit.net ⁨4⁩ ⁨months⁩ ago

    youtube.com/watch?v=vmRDcXADnbA

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• ArbiterXero@lemmy.world ⁨4⁩ ⁨months⁩ ago

  32 bit CPU’s having difficulty accessing greater than 4gb of memory was exclusively a windows problem.

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  • aard@kyu.de ⁨4⁩ ⁨months⁩ ago

    You still had a 4GB memory limit for processes, as well as a total memory limit of 64GB. Especially the first one was a problem for Java apps before AMD introduced 64bit extensions and a reason to use Sun servers for that.

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    • ArbiterXero@lemmy.world ⁨4⁩ ⁨months⁩ ago

      Yeah I acknowledged the shortcomings in a different comment.

      It was a duct take solution for sure.

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  • amanda@aggregatet.org ⁨4⁩ ⁨months⁩ ago

    Interesting! Do you have a link to a write up about this? I don’t know anything about the windows memory manager

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    • pivot_root@lemmy.world ⁨4⁩ ⁨months⁩ ago

      Here’s the compiler flag for it.

      Finding the reason for its existence from a credible source isn’t as easy, however. If you’re fine with an explanation from StackOverflow, you can infer that it’s there because some programs treat pointers as signed integers and die horribly when anything above 7FFFFFFF gets returned by the allocator.

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    • ArbiterXero@lemmy.world ⁨4⁩ ⁨months⁩ ago

      Intel PAE if the answer, but it still came with other issues, so 64 was still the better answer.

      Also the entire article comes down to simple math.

      Bits is the number of digits.

      So like a 4 digit number maxes out at 9999 but an 8 digit number maxes out at 99 999 999

      So when you double the number of digits, the max size available is exponential. 10^4 bigger in this case. It just sounds small because you’re showing that the exponent doubles.

      10^4 is WAY smaller than 10^8

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    • neclimdul@lemmy.world ⁨4⁩ ⁨months⁩ ago

      It was actually 3gb because operating systems have to reserve parts of the memory address space for other things. It’s more difficult for all 32bit operating systems to address above 4gb just most implemented additional complexity much earlier because Linux runs on large servers and stuff. Windows actually had a way to switch over to support it in some versions too. Probably the NT kernels that where also running on servers.

      A quick skim of the Wikipedia seems like a good starting point for understanding the old problem.

      en.m.wikipedia.org/wiki/Wikipedia

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    • lemmyvore@feddit.nl ⁨4⁩ ⁨months⁩ ago

      en.wikipedia.org/wiki/Physical_Address_Extension

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  • Blue_Morpho@lemmy.world ⁨4⁩ ⁨months⁩ ago

    I’m not sure what you are talking about. Linux got PAE in 1999. Windows XP got PAE in 2001.

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  • Moobythegoldensock@lemm.ee ⁨4⁩ ⁨months⁩ ago

    Not really, Raspberry Pi had that same issue with its 32 bit distros.

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• amanda@aggregatet.org ⁨4⁩ ⁨months⁩ ago

  The comments on this one really surprised me. I thought the kinds of people who hang out on XDA-developers were developers. I assumed that developers had a much better understanding of computer architecture than the people commenting (who of course may not be representative of all readers).

  I also get the idea that the writer is being vague not to simplify but because they genuinely don’t know the details, which feels even worse.

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  • sandalbucket@lemmy.world ⁨4⁩ ⁨months⁩ ago

    I think it’s a D-tier article. I wouldn’t be surprised if it was half gpt. It could have been summarized in a single paragraph, but was clearly being drawn out to make screen real-estate for the ads.

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    • SaltySalamander@fedia.io ⁨4⁩ ⁨months⁩ ago

      The majority of articles I come across are exactly like this, needlessly drawing everything out to maximize word count and, thus, maximize ad space.

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• irotsoma@lemmy.world ⁨4⁩ ⁨months⁩ ago

  Because computers have come even close to needing more than 16 exabytes of memory for anything. And how many applications need to do basic mathematical operations on numbers greater than 2^64. Most applications haven’t even exceeded the need for 32 bit operations, so really the push to 64bit was primarily to appease more than 4GB of memory without slow workarounds.

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  • tunetardis@lemmy.ca ⁨4⁩ ⁨months⁩ ago

    I know a google engineer who was saying they’re having to update their code bases to handle > 16 exabytes of storage, if you can imagine. But yeah, that’s storage, not RAM.

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    • Appoxo@lemmy.dbzer0.com ⁨4⁩ ⁨months⁩ ago

      I would kind of enjoy the trouble of needing to store and owning the place for 16 exabytes…

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• vane@lemmy.world ⁨4⁩ ⁨months⁩ ago

  tell that to playstation2 owners

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• dlundh@lemmy.world ⁨4⁩ ⁨months⁩ ago

  Dreamcast disagrees. www.consoledatabase.com/…/segadreamcast/ /s

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  • DAMunzy@lemmy.dbzer0.com ⁨4⁩ ⁨months⁩ ago

    Was that a marketing thing? Because the SH-4 was only 32-bit AFAIK.

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    • magic_lobster_party@kbin.run ⁨4⁩ ⁨months⁩ ago

      Only thing I can find is that it has 128-bit graphics-oriented floating-point unit delivering 1.4 GFLOPS.

      Probably only for marketing reasons. Everyone was desperate not to be worse than N64.

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    • dlundh@lemmy.world ⁨4⁩ ⁨months⁩ ago

      Yes.

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  • stembolts@programming.dev ⁨4⁩ ⁨months⁩ ago

    So cool.

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• djehuti@programming.dev ⁨4⁩ ⁨months⁩ ago

  We do. Next question.

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  • kilgore_trout@feddit.it ⁨4⁩ ⁨months⁩ ago

    Why are we not using them in end-user devices

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    • ms_lane@lemmy.world ⁨4⁩ ⁨months⁩ ago

      We are.

      Addressing-wise, no we don’t have consumer level 128bit CPUs and probably won’t ever need them.

      Instructions though, SSE had some 128bit ops (OR/XOR, MOVE) and AVX is 128bit vector math. AVX2 is 256bit vector math, AVX512 is- you guessed it 512bit vector math. AltiVec on PPC had 128bit vectors 20 years ago.

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    • db2@lemmy.world ⁨4⁩ ⁨months⁩ ago

      There’s no benefit.

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• mox@lemmy.sdf.org ⁨4⁩ ⁨months⁩ ago

  John Mashey wrote about this nearly 30 years ago. This Usenet thread is worth a read.

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• AmidFuror@fedia.io ⁨4⁩ ⁨months⁩ ago

  That would be like 6 minutes abs.

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  • AnarchoSnowPlow@midwest.social ⁨4⁩ ⁨months⁩ ago

    That’s crazy. You can’t do six. It’s seven! SEVEN MINUTE ABS!

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  • elbarto777@lemmy.world ⁨4⁩ ⁨months⁩ ago

    What’s this in reference to?

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    • AmidFuror@fedia.io ⁨4⁩ ⁨months⁩ ago

      There's Something about Mary (1998)

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• Etterra@lemmy.world ⁨4⁩ ⁨months⁩ ago

  Okay, so why can’t we just not use exponentially growing values? Like 96 bit (64 + 36). I’d the something intrinsic about the size increases that they HAVE to be exponential? Why not linear scaling? 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, etc.

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• unreachable@lemmy.world ⁨4⁩ ⁨months⁩ ago

  so i guess the next bit after 64 cpu is qu-bit, quantum bit

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• kerrigan778@lemmy.world ⁨4⁩ ⁨months⁩ ago

  Uh, the PlayStation 2 would like a word?

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• hades@lemm.ee ⁨4⁩ ⁨months⁩ ago

  pixelfed.social/p/sedah/710395721014627367

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• Mio@feddit.nu ⁨4⁩ ⁨months⁩ ago

  Would it be a downside? Slower? Very costly?

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• JATtho@lemmy.world ⁨4⁩ ⁨months⁩ ago

  Even the newest “64-bit” cpus are really just 48-bit (or 36-bit on low end) or if bleeding edge 56-bit physical adressing processors. This is the maximum amount of virtual memory a process can have access to. You could memory map all your hard disks an still have room to map more physical memory to VMA.

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