Comment by xoa | Hacker News Reader

Comment by xoa | Hacker News Reader

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Just doing some napkin math to give myself some other context in my own head with something much smaller, die size for the Apple A14 isn't out yet, but the A13 (found in the iPhone 11 series and SE 2) is around 98mm^2 manufactured on TSMC's 2nd gen 7nm N7P. A14 might be something like that, because while it's a smaller process Apple boosted transistor count by 38% as well. Lazily/conservatively taking off 10mm on the edge for squares into a circle, that'd be about 630 chips per N5 wafer, a high enough count that chip loss rate shouldn't be too far from defect rate. Even assuming they can get 90% yield right out the gate (maybe generous) that's still about $30/chip, just for manufacturing without any R&D amortization, packaging etc. That actually seems not insignificant going by historical iPhone BOMs [1], so even for smartphones with their far far smaller SoCs 5nm at launch isn't nothing.

The continued ongoing progress in silicon is just mindblowing when you dig into the details in any real way. I was blown away already watching the "Indistinguishable From Magic: Manufacturing Modern Computer Chips" [2] presentation years ago, which still seems incredible and yet that's all talking about now ancient tech. The increasing costs and design challenges though are also going to have interesting effects on the industry, as who/what has the margins to afford fabbing aggressive chips on the cutting edge might start to diverge a bit more. I also wonder how longevity will be, I remember speculation that smaller processes would eventually have to deal with more risk of earlier breakdown even in more normal shielded settings. And speaking of that, in higher rad environments it's normal to use older bigger processes since they're more resistant to disruption. I wonder if small enough processes ever make that more of a consideration even at sea level.

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1: iPhone Xs Max for example: https://technology.informa.com/606680/iphone-xs-max-costs-ap...

2: https://www.youtube.com/watch?v=NGFhc8R_uO4 (highly recommended if you haven't seen it)

> And speaking of that, in higher rad environments it's normal to use older bigger processes since they're more resistant to disruption.

This was mostly debunked in https://news.ycombinator.com/item?id=24430234 with some nuance.

> Even assuming they can get 90% yield right out the gate (maybe generous)

That seems outrageously generous. Rememember that Apple doesn't (as least hasn't so far) bin their parts to sell the ones with faults via different configurations. The only way to get a chip yield like that for a single device configuration is with a ton of redundancy.

I certainly don't know what the yield rate is of Apple silicon, but I definitely don't believe 90%.

>That seems outrageously generous.

Probably, but until we actually get some A14 die shots I don't know how aggressive Apple has been with caches and the like with some redundancy that can be fused off for yield. Again though all the numbers are napkin math and trying to give some fudge factor in both directions, so conservative on the number of chips total (I didn't try to calculate exactly how many full squares fit I just took off an entire outer radius) and generous on the yield. Mainly I was trying to reason about the question of "even if everything goes great, and even if it's something smaller not a monster desktop GPU or the like, is it still a non-trivial cost?" to which it seems like the answer is yes. If it's actually a smaller yield that just makes it get even more expensive, but yield itself won't be a silver bullet.

Usual yields are quoted at 60-75%. More for smaller chips. But can you even tell how many cores are actually running in your iPad? Maybe they do fuse out a faulty one.

On modern chips, we are not only "fusing out" faulty cores. We also put more memory cuts than necessary into the silicon and we fuse out the defective ones to increase the yield. You can look at Memory BISR (built-in-self-repair).

If Apple wanted to bin the chips, they have devices crying out for low-power draw, albiet slower clock. They can sell a tonne of earphones, watches, HDMI enabled USB-C dongles. They could re-purpose chips which can clock 10x slower for 1/2 the cores, and still have too much CPU. But free.

They can use them for the Apple touchpad, the keyboard, the on-mobo controllers which currently consume non-general-purpose chips, if they want to. If they displace a 10c part by an otherwise redundant $30 part, they are still ahead, if it works.

The power draw for a full blown chip like A13 is vastly different from that of the typical ones you find in the devices you mentioned. Also the form factor could limit for many of the smaller devices

Yes, I realised this was stretching the argument after I posted. Probably, repurposing terminates in slower, lower spec devices the A13 targets anyway. Maybe in something like the Apple TV?

It would be true that compared to Intel they have far less binning opportunities

One way to bin it would be:

Macbook -> iPad -> iPhone -> Apple TV

Not sure if they still are, but for a while they were shipping Apple TV's with Apple CPUs which had half the number of working cores, but they were running it with higher thermal limits.

> If they displace a 10c part by an otherwise redundant $30 part, they are still ahead, if it works.

I am no expert, but my intuition says that even die size alone would present a problem.

Are Non-Pro iPhone and cheaper iPad not using slower clocked chip?

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