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Comment by userbinator | Hacker News Reader

This is important as any 32 bit design is already going to be a big project, so lets not make it impossible by going for something like the CISC of the 80386!

From a practical standpoint, going with 32-bit over 16-bit means not much more than making the datapath twice as wide --- which increases area but not actual complexity per se. And seeing a discrete i386 would actually be pretty interesting, especially if implemented on top of this one as an x86-to-RISCV uop-based decoder like the original P5.

Here's another well-known one, although it's 16-bit and uses a custom ISA (but its creator ported a whole OS to it):

http://www.homebrewcpu.com/

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> From a practical standpoint, going with 32-bit over 16-bit means not much more than making the datapath twice as wide

Actually, that is more true from a theoretical standpoint.

From a practical standpoint you have twice as many traces to fit on your board and route, you have more chips, higher power requirement, etc.

So very true. I have an ongoing 32-bit computer project using a simple MPU and RAM/ROM/peripherals attached via a standard bus, and oh my god is that ever a lot of signals. It's not as bad if you use big device packages, but at higher speeds and with now-common BGA parts, it is damn hard to route all those signals with the processes that are easily available to hobbyists (like OSH Park's four layer board service).

It's unfortunate that hobbyist PCB processes haven't increased much in layer count vs, price even after several decades; the original IBM PC (8-bit data/16-bit address, multiplexed), if my sources are accurate, used a 4-layer motherboard. 386/486-era motherboards with real 32-bit busses, already had 6-8 layers. It seems cost goes up more than the multiple of the layer count --- a 10-layer board costs more than 5x a 2-layer one.

I feel like there has been considerable improvement in the hobbyist PCB scene... Prices, process size, and turnaround time for low layer count boards have come way down. But still, like you say, >4 layer stuff gets crazy expensive fast. Maybe easy access to higher layer counts will be the next milestone.

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