My Second Mac - test-drb@ccmp.vtda.org

7 Jan 2007

...
  On Sun, 7 Jan 2007, Scott Quinn wrote:
  My guess has to do with processors: i80486
binaries can run just fine
 on Pentium+ systems. 
 so can 8088 binaries.  (With occasional exceptions that don't typically
 show up in common usage (such as PUSH SP))
 But not all Pentium+ binaries will run on 8088, or even i80486.

 There seemed to have been a cultural difference between Motorola and
 intel.

 Motorola would design each major generation from scratch, thus 
 producing a
 much better processor, but without legacy software.

 intel, OTOH, would bend over backwards to try to maintain 4004
 compatibility. 
We're talking about two slightly different things here, though- 68000 
(while it did not have provisions for easily running 6800 code) had a 
common-mode so that programs built on the 68040 could run on the 68000, 
but you can also have code that requires instructions (or other things) 
added on later 68000-series processors, similar to Intel (variable 
286-style segments, the copy-on-write provision of the 80486, etc.). 
The transition between 68000 and PPC was more like the Intel gap 
between the x86 and the 960 - they are completely different processors 
with no common heritage (the common heritage piece was provided by 
Apple in firmware). I haven't worked with them, but AFAIK the new 
embedded versions of the 68000 (ColdFire?) maintain the tradition of 
working with earlier 68ks (except in a few cases).