this post was submitted on 23 Jun 2024
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[–] wewbull@feddit.uk 67 points 3 months ago* (last edited 3 months ago) (13 children)

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

Some people called it a 16/32 bit processor, but really it was the 16-bit ALU that classified it as 16-bits.

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)? Do you want to multiply those numbers up by the number of ALUs in a core? ...by the number of cores on a piece of silicon?

Me, I'd say Zen4 was a 256-bit core, but you could argue any of the above numbers.

Basically, it's a measurement that lost all meaning so people stopped using it.

[–] LeFantome@programming.dev 18 points 3 months ago* (last edited 3 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 rely on 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.

[–] Blackmist@feddit.uk 14 points 3 months ago (1 children)

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.

[–] SlothMama@lemmy.world 4 points 3 months ago

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

[–] 9488fcea02a9@sh.itjust.works 5 points 3 months ago (1 children)

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

[–] wewbull@feddit.uk 5 points 3 months ago (2 children)

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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[–] ZILtoid1991@lemmy.world 5 points 3 months ago

With AMX, now we have 1024 bit processors!

[–] Buffalox@lemmy.world 5 points 3 months ago* (last edited 3 months ago) (1 children)

At less than a tenth the size, this is actually a better explanation than the article. Already correcting the fact that we do at the very beginning.
If you absolutely had to put a bit width on the Zen 4, the 2x128 bit data bus is probably the best single measure totaling 256 bit IMO.

[–] wewbull@feddit.uk 4 points 3 months ago (1 children)

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?

[–] Buffalox@lemmy.world 5 points 3 months ago

Yes you are 100% right, and I did consider level 3 cache as a better measure, because that allows communication between cores without the need to go through RAM, and cache generally has a high hit rate. But this number was surprisingly difficult to find, so I settled on the data bus.
Anyways it would be absolutely fair to call it 256bit by more than one measure. But for sure it isn't just 64 bit, because it has 512 bit instructions, so the instruction set isn't limited to 64 bit. Even if someone was stubborn enough to claim the general instruction set is 64 bit, it has the ability to decode and execute 2 simultaneous 64 bit instructions per core, making at least 128 bit by any measure.

[–] CetaceanNeeded@lemmy.world 4 points 3 months ago (1 children)

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

[–] wewbull@feddit.uk 7 points 3 months ago

Yes, because 256 memory locations is a bit limiting.

[–] deddit@lemmy.world 4 points 3 months ago

So, you're saying it already goes to '11'?

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[–] hades@lemm.ee 26 points 3 months ago (5 children)

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?

[–] TonyTonyChopper@mander.xyz 39 points 3 months ago (2 children)

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

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[–] Liz@midwest.social 16 points 3 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!

[–] kayazere@feddit.nl 10 points 3 months ago (6 children)

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

[–] Surreal@programming.dev 3 points 3 months ago (1 children)
[–] bitwaba@lemmy.world 3 points 3 months ago

More wheels!

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[–] borari@lemmy.dbzer0.com 3 points 3 months ago (1 children)

Some of us drive 18-wheeled vehicles.

[–] randombullet@programming.dev 3 points 3 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.

[–] just_another_person@lemmy.world 17 points 3 months 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.

[–] Voroxpete@sh.itjust.works 22 points 3 months ago (1 children)

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.

[–] Cocodapuf@lemmy.world 16 points 3 months ago* (last edited 3 months ago) (1 children)

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."

[–] mitrosus@discuss.tchncs.de 3 points 3 months ago

Learned from the teacher. Thanks.

[–] jwr1@kbin.earth 13 points 3 months ago (1 children)

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.

[–] fmstrat@lemmy.nowsci.com 9 points 3 months ago

Comment OP must never learn anything new. Good find.

[–] Technus@lemmy.zip 9 points 3 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.

[–] otp@sh.itjust.works 5 points 3 months ago

Is this a question?

Woah, meta.

Yes, it is.

This is not a question, though.

[–] Cethin@lemmy.zip 4 points 3 months 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.

[–] sugar_in_your_tea@sh.itjust.works 3 points 3 months ago (1 children)

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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[–] vane@lemmy.world 6 points 3 months ago

tell that to playstation2 owners

[–] irotsoma@lemmy.world 6 points 3 months ago (7 children)

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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[–] amanda@aggregatet.org 5 points 3 months ago (1 children)

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.

[–] sandalbucket@lemmy.world 5 points 3 months ago (1 children)

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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[–] AmidFuror@fedia.io 3 points 3 months ago

That would be like 6 minutes abs.

[–] djehuti@programming.dev 3 points 3 months ago (3 children)
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[–] dlundh@lemmy.world 2 points 3 months ago (3 children)
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