[geeks] The best things in the world

[Geoffrey S. Mendelson]

On Thu, Sep 11, 2008 at 05:07:44PM -0400, der Mouse wrote:
>Indeed, I suspect that the causal relationships are pretty tangled.
>Part of it is probably UCB releasing a non-encumbered BSD; part of it
>is probably general uptake of computers, and in particular the
>availability of cheap and relatively powerful mass-market hardware;
>there are doubtless plenty of other parts too.

The singular thing that caused the growth of *NIX systems to the point where
they are today was the release of the 80386 chip. 

Before that Intel processor chips had two problems which made them unsuitable
for these type systems, but there were several attempts to live within
their limitations.

The first was the "address space". The 8086 and it's children all were
limited to 64k of address space. You had to address memory by referring to
a segment register and a displacement of up to 64k. There were two segment
registers, one for program instructions and one for data.

The 80386 included a "flat" address space. This mean that you could refer
to a byte in memory by it's complete address, without using a segment
register. The registers still existed and were used, but the you could now
use direct pointers and have arrays larger than 64k without a lot of effort.

The other is protected mode. The 80286 introduced it, which included
access to memory beyond 1 megabyte, but it had some limitations in what
would work. It was easy to get into protected mode, but impossible to
get out. To get out you had to reset the processor.

The inclusion of a memory management chip which allowed for paged virtual
memory helped too. :-)

If any of you remember Coherent or Xenix from those days, they were limited
to 64k segments. In order to get a usable screen based newsreader for
Coherent (286), I had to write one.

Geoff.

-- 
Geoffrey S. Mendelson, Jerusalem, Israel gsm at mendelson.com  N3OWJ/4X1GM