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Comment by cogman10 | Hacker News Reader

With the current silicon manufacturing processes, I'd say the end is in sight. Every node shrink is taking longer and longer and getting more and more expensive to fabricate.

We've been reliant on node shrinks to push things further. That hard limit is 0.2nm (silicon atom size) we are at ~2nm gate features.

It remains to be seen if we can get to that 0.2nm size, I honestly don't think we can push much further past the 2nm size (I'd imagine 0.5nm will be the limit).

That, to me, is very much being "in sight".

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3d chips. Imagine current size with 1 million layers. Sure it will start with just a few layers. And many obstacles to be overcome like temp and delay. But one day our cpus will look like little cubes. Moore's law can continue for at least another 30 years

Couple of problems.

First, how do you cool such a chip? Sure, you could add a bunch of transistors but the thermal costs per transistor will stay the same. Assuming similar design but adding 20 layers, how would you account for your CPU now consuming 600W?

Second, The tech doesn't exist. The problem we have is that layering chips today is basically growing crystals in a controlled fashion. Defects in lower layers spoil upper layers. Today that's already a problem (CPUs today have ~7 or 8 layers). Can you imagine the problem of 20 or 30 layers?

Who knows, maybe we'll come up with solutions to both problems, but that's a big maybe. My bet is that instead we focus on architecture designs. We revisit old but deemed too expensive concepts like an async CPU.

This is real, shipping technology.

See 3d nand flash cells, see stacked cache and HBM memory. All the usual characters are working on it. Intel, AMD (TSMC), Samsung.

Cooling is an issue, but there are solutions.

3d cells for nand aren't the same as 3d CPU cores. Nand is incredibly simple which makes it possible to do things like 3d cells which would otherwise be more complicated.

There's a reason memory can generally beat computational cores to smaller node sizes. It's because highly uniform circuits are much easier to manufacture. A lot of problems present in CPU logic cores (such as cross talk) just aren't present to the same extent in NAND cells.

Maybe stuff like Upmem (many small CPUs embedded into memory) can take off then?

Possibly, that'd be one of the "major architectural changes" that I mentioned earlier. Things we've simply not tried yet because they are too radically different from the way hardware currently works.

Sorry to have to ask.Could you please show a Wikipedia-like intro to Upmem?

It may be a simple typing problem, but Wikipedia doesn't seem to have it.

I found a previous HN submission about them: https://news.ycombinator.com/item?id=20766283

> Today that's already a problem (CPUs today have ~7 or 8 layers).

No, I think x86 passed 14+ layers at least half a decade ago.

So I'm behind :D. What I remember is them trying to cut down the layers due to yield issues. Guess it's creeped back up again.

That's a continuation of moore's law, it's the same as having a bigger chip horizontally, or more chips. You can make giant chips but you need giants bank accounts.

It does not reduce price per transistor because each layer still has to be manufactured the same way

Sort of true, except you can use cheaper process scales for some of the layers.

The silicon is not actually the expensive part.

There are still many ways this may change. 3d transistors (which are currently used), different materials, and 3d chips (stacking layers of chips).

We are not yet close enough to the end to say where it is, so that's out of sight IMHO.

Like I said, cooling is going to be a major issue that doesn't currently have a solution (as far as I know) Even if it does, you are going to run into the real problem that even if you can cool a 600W CPU, would the average customer WANT to have such power hungry parts? Now imagine the problem in server space where the CPUs are already constrained by power consumption.

The entire reason cloud service providers are looking at and advertising ARM racks is the power savings from operating them.

I think there are almost endless gains to be had on the software side. Current software is so insanely inefficient you could probably triple the speed of the average computer without any hardware upgrade.

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