Re: Apple Drops Backward Compatibility for Next MacOS

[dempson@actrix.gen.nz (David Empson)]

Ralph Wade Phillips <ralphp@gcstation.net> wrote:

> Hi, Hans!
> 
> In article <3275d8f5.865949@news.wantree.com.au>, hansie@wantree.com.au
> (Hans Klarenbeek) wrote:
> 
> > On 26 Oct 1996 21:53:03 GMT, pubpc1@library.ucla.edu wrote:
> > 
> > >Randy, the Pentiums are based on 8-bit processors too, if you think about
> > >it that way!  Have you ever studied the architecture of the 8088/8086?
> > 
> > The instruction are based on the 8088.....
> 
>         .... whose instructions are based on the 8080, whose instructions
> are based on the 8008, whose instructions are based on the 4004, a 4-bit
> processor!

But only loosely.  The 80386 instruction set is object compatible with
that of the 8086, or existing instructions are redefined to work in new
ways in protected mode (e.g. 16-bit register accesses are changed to
32-bit register accesses unless an override is used).

The 8086/8088 instruction set and architecture is nothing like that of
the 8080.  Some concepts remain (e.g. the parity flag) but they are more
different than they are similar.

(I've never worked with an 8008 or 4004 so I don't know how much they
have in common with an 8080.)

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand