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Comment by realo | Hacker News Reader

Yes, modern computers are fast. How fast?

The speed of light is about 300,000 km/s. That translates to roughly 1 ns per foot (yeah, I mix up my units... I'm Canadian...)

THUS, a computer with a clock speed of 2 GHz will be able to execute, on a single core/thread, about 4 (four !) single-clock instructions between the moment photons leave your screen, and the moment they arrive into your eye 2 feet (roughly) later.

_That_ should give you an idea of how fast modern computers really are.

And I _still_ wait quite a bit when starting up Microsoft Word.

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The obvious conclusion is that by doubling your distance to the screen, you double your computers speed! ;-)

(in truth, I really like this image, though. On a similar note, I think I recently saw a number for the length of wiring in a modern cpu (ryzen review perhaps) - and it was a rather staggering number from the fractal layout of modern chips - 200 meters perhaps? In a square little more than 2 cm to a side, if that?)

Another fun start I recently learned is that about half of the area on the die on a modern chip is taken up by wires for the clock alone, in large part to ensure the length of wire to each component is the same length.

http://m.cacm.acm.org/magazines/2017/1/211094-exponential-la...

Holy crap, you're right. 2 instructions per light-foot! That is a very cool comparison!

Makes me think maybe light is slower than I thought. And that Word must have a lot of code running. :P

Most modern CPU's can execute more than one instruction per clock cycle on a single core or hardware thread. They do a lot more than 4 instructions in the time light can travel 2 feet.

Also: While SIMD does not execute additional instructions, it executes more operations [that's the whole point; it reduces contention and bandwidth needs in the frontend / instruction decoding and scheduling]. A Haswell core peaks at 32 SP FLOP/cycle, for example.

If you want to get technical, modern CPUs can dispatch (begin the execution) of 4 to 6 instructions every clock cycle. However, many instructions take more than one cycle to complete. For instance, integer multiply takes 3-4 cycles on an Intel Sandy Bridge chip. FMUL takes 5 cycles to complete.

That being said, there are several instructions, like mov, integer additions and compare, bitwise operations, which can absolutely complete in a single cycle.

See this document for more details: http://www.agner.org/optimize/instruction_tables.pdf

This (appx 1ns / foot) was Grace Hopper's visualization many years ago. I remember being taught it in 1990 and intrigued at how it made something abstract so easily memorable.

The thing is that while CPUs are fast, RAM, never mind a HDD, are not.

This is the coolest fact, how incredibly fast they can react.

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