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Comment by kens | Hacker News Reader

Author here. I hope you're not tired of the 386... Let me know if you have any questions.

I'll never tire of any analysis you do. But if you are taking requests, I'd love two chips.

The AMD 29000 series, a RISC chip with many architectural advances that eventually morphed into the K5.

And the Inmos Transputer, a Forth like chip with built in scheduling and networking, designed to be networked together into large systems.

https://en.wikipedia.org/wiki/AMD_Am29000

https://en.wikipedia.org/wiki/Transputer

Those would be interesting chips to examine, if I ever get through my current projects :-)

If you are doing requests, I'd love to see the M68k series analyzed.

Another vote for the 68000 series :)

I have some Transputer die and die plots if you ever need those.

Have you thought about doing these yourself?

Great question. I have and I should.

This would make concrete and bring coherence to the grab bag of skills and experience I have. Though I think it would be 10x as much in a small group setting. It is like trying to recover the source code a binary where you don't even know the source language.

https://www.youtube.com/watch?v=M3nFcTpAwoM&list=PLUg3wIOWD8...

That would be awesome!

At what number of layers is it difficult to reverse engineer a processor from die photos? I would think at some point, functionality would be too obscured to able to understand the internal operation.

Do they ever put a solid metal top layer?

I've been able to handle the Pentium with 3 metal layers. The trick is that I can remove metal layers to see what is underneath, either chemically or with sanding. Shrinking feature size is a bigger problem since an optical microscope only goes down to about 800 nm.

I haven't seen any chips with a solid metal top layer, since that wouldn't be very useful. Some chips have thick power and ground distribution on the top layer, so the top is essentially solid. Secure chips often cover the top layer with a wire that goes back and forth, so the wire will break if you try to get underneath for probing.

Interesting! What is the reason of 800nm limit? I have successfully photographed my own designs down to 130nm with optical microscobes, though not with metal layer removal. The resolution isn't perfect but fearures were clearly visible.

The first thing I thought he was referring to is the wavelength of optical light, which is generally between 800-400nm IIRC. I take it your 130nm optical microscopes are imaging using ultraviolet? Regardless, let's just get this man a scanning tunneling microscope already. :D

I'd love to see an analysis of byte ordering impact on CPU implementation. Does little vs big endian make any difference to the complexity of the algorithms and circuits?

Never, the 386 is way too important.

So Epictronics recently looked at the 386SX, the version with the 16bit external bus, which was slower than the 286 at the same clock. What changed between that and this? Was the major difference the double clock hit on fetch? Or did it have a shorter prefetch queue as well like the 8088?

386SX was slower than a 286 at the same clock only for the legacy 16-bit programs and only for the 16-bit programs that did not use a floating-point coprocessor, as the 80387 coprocessors available for 386SX were much faster at the same clock frequency than the 80287 available for 286.

Moreover there was only a small time interval when 286 and 386SX overlapped in clock frequency. In later years 286 could be found only at 12 MHz or 16 MHz, while 386SX was available at 25 MHz or 33 MHz, so 386SX was noticeably faster at running any program.

Rewriting or recompiling a program as a 32-bit executable could gain a lot of performance, but it is true that in the early years of 386DX and 386SX most users were still using 16-bit MS-DOS applications.

Ok, now do 486.

I'm not as interested in the 486; I went stright to the Pentium: https://www.righto.com/2025/03/pentium-multiplier-adder-reve...

Fair enough. But why?

Because I saw a Navajo weaving of a Pentium and wanted to compare the weaving to the real chip: https://www.righto.com/2024/08/pentium-navajo-fairchild-ship...

I was only joking but I'm glad you have decided to take it seriously.

That was great. Thank you.

Too bad (for the Navajo Nation) about the armed standoff and its aftermath.

I totally agree with your methodology. Stick to the classic leaps.

Never!

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