Comment by ggm | Hacker News Reader

Comment by ggm | Hacker News Reader

To me, The 6502 kind of represented best-of-breed but a bit of a dead end. I couldn't see a 16-32 bit story. It's like it hit the spot, and stopped growing.

The 6800 begat the 68000. It had virtual memory management. That launched ten or more models of workstation and hit the magic '3M' window: a MIP, a Megabyte of memory and a Million pixels. 68000 led to SPARC because Sun decided to go into the RISC business itself.

I used Motorola workstations alongside Sun, for a Cray-1 project I was on the periphery of: they were the ones Cray shipped to us, passing the Cray-1 on from another customer (Boeing) and they were fine, if remarkably (physically) large machines. Like they'd got the idea of "this is a workstation" in the Microvax era, and never quite shrunk down.

I had a 6502 box (the Acorn Atom, a precursor to the BBC micro) and I used others, But I kind of wished the 6800/0 series had been bigger, and we'd been in that world more than Intel. it was nicer. it felt nicer. It felt like an instruction set Gordon Bell would have liked. It made sense if you came from a pdp-11.

Maybe I'm addicted to network byte order computers.

> It's like [6502] hit the spot, and stopped growing.

Indeed. In fact, Acorn played around with a couple of successor candidates like national semiconductor 32016 (and even Intel 80186) using the BBC micro's Tube interface before they finally have up and developed the ARM chip.

In a sense, ARM (initially Acorn RISC machine) is "the true" 6502 successor. Having done assembly on both BASIC II and V (on Archimedes) the legacy in arm2 Isa was quite evident.

i really don't think the 6800 begat the 68000 - they have almost nothing in common, architecture-wise. on the other hand, the intel 8080 certainly connected to the 8086 and in fact a lot of 8086 programs were mechanically translated, at least in part, from the 8080 (and z80).

Look I get this, its not like one is backwards compatible to the other. But the 68000 exists because Motorola were invested in the 6800 and saw a path onward, albiet leapfrogging to 32 bits, and deliberately not doing backwards compat ISA.

Intel and Zilog took another path. Their path in some ways, was the wiser course because IBM jumped on the Intel model and .. here we are. Zilog couldn't make it work as well for them as Intel did.

I don't really get that. The 6800 begat the 6809, and that was the connection to the 6800. When Motorola made the 68000 they decided to begin with a clean slate, there's really nothing in connection with the 6800 except the numbering scheme and both being big endian. If you want to use the word 'begat' then it fits Intel much more. Intel made the 8086, and Mensch made the 65816, both went for backwards compatibility (source or architecture) to some extent (which gave us segments and other negative artifacts).

So yes we agree on the facts, it's just so strange that you in your previous post said that the "6800 begat the 68000" - if anything, it didn't. All the companies went ahead with 16- and / or 32-bit CPUs, the difference is that Motorola broke away from their 8-bit past while doing so.

> the difference is that Motorola broke away from their 8-bit past while doing so.

And then they did it again with the PowerPC (and the 88000 prior to that) which had very little in common with the 68k.

They actually have many details in common, including some suboptimal choices, like the handling of the flags, but those are not due to 68000 being derived from 6800, as there was no such direct connection, but due to the fact that both the 6800 and the 68000 ISAs have been strongly influenced by the DEC PDP-11, which was the most popular minicomputer during the seventies.

Due to very similar mnemonics, the assembly languages of MC6800 and of MC68000 resemble even more the PDP-11 assembly language than their actual instruction sets.

>I couldn't see a 16-32 bit story. It's like it hit the spot, and stopped growing.

And yet WDC (Bill Mensch's company post-Commodore) put out the 65816, a 16-bit expansion of the 6502 that was the core of the Super Nintendo. So it still grew even if not to 32-bit level.

And the Apple IIGS where it was allegedly underclocked so as not to horn in on the Macintosh.

I wonder what might have been if MOS had shipped a 16-bit 6502 in 1980 instead of WDC shipping one in 1985.

Oh, I bet you'd have loved the TMS 9900. Tons of registers with switchable windows, mini-computer oriented ... and big-endian.

Looks good, but from a business perspective, another dead end -What I read says TI decided to get out of the general CPU business. Probably it means they couldn't find somebody interested in buying into this ISA and chipset to sustain their investment in developing it, where they had solid business in the other specialised spaces.

Yes, heaps of registers which map into the address space means (I am guessing) simple C compiler and Unix porting, once virtual memory is there. I wonder why nobody ran with it?

The TI-99/4A was atrocious on many level, but the reason for the abysmal performance is well documented on Wikipedia -- the architecture was inherited from TI-990 which assume fast 16-bit memory and TMS9900 had neither.

Looking at the specs for the TI TMS9900, Zilog Z80, and the MOS 6502, the TI chip came in a 64-pin DIP and required +5V, -5V, and +12V power supply while the other two chips came in a 40 pin DIP package and only required a +5V power supply.

The 6502 was cheap (<$30), the Z80 was more expensive at introduction, but looking at price lists, dropped down close to the same price as the 6502 within a few years.

from https://www.cpushack.com/2015/02/05/ti-tms9900sbp9900-accide...:

" In 1978 a 9980 cost $30 while a TMS9900 cost $70."

Also, in the comments from the above link:

"Many years later, the processor architect for the TMS9995 (Karl Guttag) pointed out to me that whatever context switch benefits the WP offered were quickly outweighed by the required memory access cycles only a handful of instructions into an interrupt service routine. It was a false economy."

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