4 ms·

I'm curious if anytime soon we'll start seeing optical interconnections between CPUs and on-device / same-chasis memory. I'm not sure what that would add for l

I'm curious if anytime soon we'll start seeing optical interconnections between CPUs and on-device / same-chasis memory. I'm not sure what that would add for latency and cost, but I'm guessing that with optical wave guides, crosstalk isn't a concern. At least for the optical part of the data path.

kimixa 3y ago
The speed of light in an optical fiber is still only about 2*10^8 m/s - ddr5 6000's 3ghz clock means it still only travels 6.7cm/clock - so there'll still be difficulties around latency if it's not "close", and that's ignoring any issues of actually getting optical transceivers on the die itself.
- billti 3y ago
  It blew my mind when I learned that even if you could hand wire conceptually perfect switches and wires, once your board was over a few inches, the laws of physics (e.g., the speed of light) would mean you still couldn’t beat a modern CPU for clock speed. It really is insane the level at which current hardware works.
  - josephg 3y ago
    Yeah. Any time I wait for my computer to do something I think about this. In the 4 seconds discord took to open, my computer could do what, 5 billion operations per second per core? Even single threaded that’s 20 billion steps? And my internet connection could have delivered 600 million bytes of data - enough for a complete copy of windows xp. It’s wild.
    - steve1977 3y ago
      It’s wild and a sign how terribly inefficient most software is today
trealira 3y ago
> I'm curious if anytime soon we'll start seeing optical interconnections between CPUs and on-device / same-chasis memory. Isn't that kind of what those APUs sold by AMD are? And SoCs? I could be misunderstanding you, though.
ta988 3y ago
They are coming yes. They may not bring much in term of bandwidth per line, but will allow much more lines and entirely different geometries for the cpus allowing chips to be cooled on both sides etc.

kimixa 3y ago

The speed of light in an optical fiber is still only about 2*10^8 m/s - ddr5 6000's 3ghz clock means it still only travels 6.7cm/clock - so there'll still be difficulties around latency if it's not "close", and that's ignoring any issues of actually getting optical transceivers on the die itself.

billti 3y ago
It blew my mind when I learned that even if you could hand wire conceptually perfect switches and wires, once your board was over a few inches, the laws of physics (e.g., the speed of light) would mean you still couldn’t beat a modern CPU for clock speed. It really is insane the level at which current hardware works.
- josephg 3y ago
  Yeah. Any time I wait for my computer to do something I think about this. In the 4 seconds discord took to open, my computer could do what, 5 billion operations per second per core? Even single threaded that’s 20 billion steps? And my internet connection could have delivered 600 million bytes of data - enough for a complete copy of windows xp. It’s wild.
  - steve1977 3y ago
    It’s wild and a sign how terribly inefficient most software is today

trealira 3y ago

> I'm curious if anytime soon we'll start seeing optical interconnections between CPUs and on-device / same-chasis memory. Isn't that kind of what those APUs sold by AMD are? And SoCs? I could be misunderstanding you, though.

ta988 3y ago

They are coming yes. They may not bring much in term of bandwidth per line, but will allow much more lines and entirely different geometries for the cpus allowing chips to be cooled on both sides etc.