Hacker News Reader

Comment by D_Guidi | Hacker News Reader

Amiga 2000 wasn't a 16bit system?

The Amiga 2000 shipped with a 7.16 (NTSC), 7.09 (PAL) Motorola 68000 CPU which was 32 bit internally with 16 external data bus.

To be a bit pedantic, the 68000 was a mostly 16-bit implementation of a 32-bit ISA. The ALU is 16-bit (though it can be ganged together with an additional 16-bit shift register for 32-bit shifts) and most of the data paths are 16-bit as well.

It's a really smart design. Combines a forward-looking architecture with a realistic implementation for the time. It's a shame it died out while x86 survived.

It took too long to go superscalar, pipelining was a bit of an afterthought, they _should_ have done more with the Apple contract. Because they didn't this meant Apple moved on to PowerPC and the bottom fell out of the 68k market.

It's sad overall really. The Amiga was a great machine with a fun and easy-to-use/manipulate operating system. Memory protection (beyond weirdnesses like Mungwall etc.) would have been nice.

For such a small team though they did very well. Commodore were desperate for a slice of that DOS/Windows PC pie though and that further drained the coffers :(

Motorola just never learned how to sit still and continue to support and extend their platform. They got early to market with the 68000 (late 70s! way ahead of its time!) but it was a totally separate ISA and platform from the (quite awesome) 6809 8-bit chip. No continuity between them. As soon as the 68k looked a bit long in the tooth they started pushing the 88k, which was a total failure. Again with no continuity. Then they jumped to PowerPC, but they never even fully committed to that either.

If they'd done what Intel did and continued to develop on the same platform, maybe they'd still exist and we've have more diversity in platforms today. The 68000 was so much nicer to develop for than x86.

I'm not an expert, but as far as I understand, what killed 68k (and many 80s CISCs, like VAX), was the difficulty with producing an OoO implementation given the very complex instruction semantics, in particular the with indirect addressing modes.

It wouldn't be a problem today as designers have transistors to spare, but it was in the early '90s, when the high performance market was taken over by the simpler OoO RISCs and x86 [1] of which, against expectations, Intel managed to build a competitive OoO implementation in the form of the PentiumPro.

[1] which compared to other CISCs is much simpler.

They ended up solving this problem eventually with ColdFire. They dropped a few instructions and addressing modes and were able to produce something pretty performant. But just 15 years too late :-)

And now that's dead too. And yeah I think the engineers at Motorola in the 90s basically just saw the RISC writing on the wall and threw up their hands and said that was the way to go, customers be damned, meanwhile Intel just had too much invested in x86 CISC and couldn't do that and so was forced to make it work.

Reply on news.ycombinator.com