muta...@gmail.com wrote:
> On Wednesday, August 31, 2022 at 6:44:56 AM UTC+8, Scott Lurndal wrote:
> > "muta...@gmail.com" writes:
> > >On Wednesday, August 31, 2022 at 2:39:56 AM UTC+8, anti...@
ath.uni.wroc.pl wrote:
> >
> > >However, what about preparation for the future
> > >by having an instruction that checks the shift value
> > >in use, and simply returning 4? Or is a
> > >processor instruction inappropriate?
> > Note to anti... he's referring to a CPUID instruction analogue.
> >
> > Note to muta... Why 4? A single bit is sufficient, and easily
> > allows future extension to describe additonal optional features.
>
> When 8 MB becomes affordable, but
> the 80386 is still not affordable, the
> shift will be 6, not 5.
>
> This continues up until you have 4 GB of
> memory. It is highly unlikely we will ever reach
> 4 GB of memory, I mean, 640 MB should be
> enough for everyone, but I believe correct
> mathematical design calls for the
> theoretical possibility of having 4 GB of
> memory.
You clearly leave in alternative universe. In alternative
universe normal logic, physics or market laws does
not work, so arguments from real world are invalid.
Still, it makes sense to say a bit about history.
> This is the conversation I expect in the Intel
> design room in 197x.
Well, if you look at electronics publications you would
find that already in early seventies it was predicted
that before 1990 it will be possible to put 360 class
processor on a single chip. So I expect Intel
engineers to look at feasiblity of providing 32-bit
processor. And they did provide one in 1981,
namely 432. AFAIK in 1982, when 286 was released
they seriously worked on 386.
Intel folks looked at many ideas, so it is possible
(evan likely) that idea of variable segment shift was
considered, but it simply lost to better ideas.
> I also expect them to conclude that they
> will make minimal effort for the 8086 itself,
> but they have a clear pathway for whatever
> the hell comes after the 8086.
>
> I expect the conversation to take an hour or two
> as they think through the implications for
> the linker etc to confirm that 4 is not
> a hard limit, and the software jackasses
> have all the required tools available if they
> bother to think it through.
>
> And even if they never make actual hardware
> that can do 5 or more bit shifts, an emulator
> may be written which can.
You still do not want to acknowlege that 286 was
superior design compared to variable segment
shift. The only drawback of 286 was limitation
to 16M of memory, but Intel understood that
with such amount of memory real world users
want 32-bit processor. So they provided one,
after failed 432 they deliverd 386. And if they
failed to deliver, there was 68000 and later
several RISC processors. Without 386 or similar
processor PC era would be history now. And 16-bit
PC era _is_ history.
BTW: Intel got really serious about binary compatibility
with 386. With 286 "well written" programs are supposed
to run unchanged in protected mode, but other had to
be fixed first. With 8086 thay provided tool to translate
8080 assembly into 8086 assembly. But instructions encodings
were quite different, so this did not help if you had only
8080 binaries (OK, you had to spend work disassembling
and then you could use the tool). And that is justified
by their market: many microprocessors run single program,
the processor was just one part of a device like printer,
monitor, disc drive etc. Since thare was single program
manufactur could spend some effort to adapt it to new
processor and what Intel provided was adequate.
--
Waldek Hebisch
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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