Why we don't have 128-bit CPUs
Why we don't have 128-bit CPUs
We went from 8-bit, to 16-bit, to 32-bit, and ended things at 64-bit. Here's why 128-bit CPUs don't exist.
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.
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.
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.
tell that to playstation2 owners
Dreamcast disagrees. https://www.consoledatabase.com/consoleinfo/segadreamcast/ /s
John Mashey wrote about this nearly 30 years ago. This Usenet thread is worth a read.