C integral types [was Re: Semi-OT: Why Kids Can't use Computers] (fwd)

[Lennart Sorensen]

On Sun, Aug 18, 2013 at 09:46:05AM -0400, D. Hugh Redelmeier wrote:
> To give it credit, the 8086 came out LONG before the 68000.
> Apparently it was good enough.
> 
> (Don't believe published "dates of introduction".  
> <https://en.wikipedia.org/wiki/Transistor_count> says that the 68000 was 
> introduced in 1979 but I got an XC68000 (engineering sample, before normal 
> production) in 1981.)
> 
> As a compiler writer, I didn't think generating code for any 8-bit 
> processor made sense -- hand-coded assembly code would be too much better.  
> The 6809 was getting there.
> 
> The 8086 was good enough to compile code for.  At least in the small
> model, all that was needed initially.
> 
> The 68k was much more expensive.  In fact the package was astonishing
> when it came out: I'd never had a 64-pin DIP before.

Yes that chip is quite big.

> The next generation was interesting too.  The 80286 had a decent on-board 
> MMU (no paging); almost no sytem ended up using that during the chip's 
> useful lifetime.  The 68020 (later) had a not-so-great optional separate 
> MMU chip so Sun built their own.

I thought OS/2 made use of it.

> When I bought my Atari ST (very new at the time) with a 68000 CPU, I 
> almost bought a cheap Taiwanese clone PC/AT instead (also new at the time) 
> with a i80286.  The MMU on the AT's 286 meant Unix could run reasonably on 
> it whereas the ST had no MMU.  The PC came with a hard drive for about the 
> same price as the ST with only floppies.
> 
> (The ST did have circuitry called an MMU.  It did nothing like what we 
> think of as an MMU, but it did one great thing: it prevented user 
> programs storing into 0, thus catching most writes through NULL pointers.)
> 
> So: dirt cheap mass-market 286 systems came out about the same time as
> cheap 68000 systems.  Comparing 8086 with 68000 isn't completely fair
> due to the different introduction dates.

But they were being considered for a new design at the same time.
So I think the comparison is fair.

> | Yeah, this is where "Beta" won (vs. VHS). :-)
> 
> ?
> 
> Intel's instruction set architecture was inferior to Motorola's.  Not
> so clear about everything else, which does tend to matter.  The 386
> instruction set was as clean as the 68k.

I have written MMU code for the 386.  What a mess.

I must admit I have never looked at the MMU code for the 68k series
(after all they didn't have it until the 68020 with the optional MMU).

They are both very much CISC.  I think these days ARM and PowerPC are
much nicer to work with.

> Beta was supposed to be better than VHS.  As an early adopter of VHS, I
> don't actually agree.  My first VCR (~$1400!) could record 6 hours,
> had extra heads with a different gap to record that in reasonable
> quality, and recorded HiFi audio in the helically scanned signal.
> Beta couldn't touch that at the time.  Of course each format
> leap-frogged, until Beta stopped bothering.

Well they did keep trying to make VHS better.  The multiple heads
did help.

-- 
Len Sorensen
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