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Comment by boznz | Hacker News Reader

No Mention of moving to 3D ?

I am assuming that having RAM and CPU (and other functions such as GPU or other hardware accelerators) on same die on different levels (physically close ie nano or micrometers apart) would cut latency by orders of magnitude.

3D is already done with NAND flash so I am assuming it is heat that is the problem.

Just my 10c

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Average distance from points in a unit circle to center is 2/3; average distance from points in a unit sphere to center is 3/4. Or if you prefer squares and cubes, you are essentially replacing a sqrt(2) diagonal with a sqrt(3) triagonal.

Even worse, surface area available for heat dissipation grows quadratically, while volume and therefore heat generated grows cubically. That's why 3D memory is a thing (most memory cells are not active at any given time), but seriously 3D processors (trigate notwithstanding) are not.

Yes, but your diameter can shrink significantly if you have more than a single plane of thickness. Currently the thickness of the die is less than 1% of the typical diameter, so that 2/3 -> 3/4 increase is negligible compared to the >100x decrease in diameter for the same number of transistors.

The biggest issue (IMO) will be heat dissipation and manufacturing time.

Well, biological brains are 3D processors, and have been a thing for billions of years..

You might be surprised how little 3D they are. Look at the top line model: the human cortex is only about 3 mm thick, and comprised of only six layers of neurons. It may look like a big lump of meat, but that's because it's folded to fit more area into the limited volume available in the skull. If you unfold it, you get this very thin sheet with a whopping area of 2500 cm^2.

It could be that CPUs are very complex and each layer adds a significant threat of errors. They are currently at around 13 layers.

It could be that the physical complexities of adding more layers is just too expensive.

That helps with wire delay but not with transistor delay. For workloads that are bound by cache latency (a lot of them) it should be a really big deal but not for more execution bound workloads. And in the end it might give a few more factors of two improvement but it will only get us so far.

> I am assuming that having RAM and CPU (and other functions such as GPU or other hardware accelerators)

We already have RAM(cache) and GPU(integrated graphics) on the same die. But that doesn't work as a replacement for professional/gaming graphical workloads.

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