Re: What Is The Difference Between 68000 Chip And 80x86 Chip?

[mjmahon@aol.com (Michael J. Mahon)]

Bryan Parkoff asked:

>What Is The Difference Between 68000 Chip And 80x86 Chip?
>
>    I have studied 6502 and 65816 microprocessor.  I am wondering about 8080
>or 8088 microprocessor.  Are both 65816 and 8088 microprocessors very
>similar, but they have different hex code for each opcodes?
>    Why do PC prefer 80x86 microprocessor such as Intel/AMD?  Also why do
>Macintosh prefer 68000 microprocessor such as Motorola?  What is the
>difference?  Which is the powerful?  I bet that Motorola microprocessor is
>much easier than Intel microprocessor.  Please advise.

Wow.  They are both microprocessors, but there is little architectural
similarity.

The x86 processors are all descendants of the 8080, and look like
the evolution of this machine on steroids.  The 68xxx processors
are more like single-chip VAXs.

The 65xx/xxx processors are another breed.  The original 6502
was a blatent ripoff of the 6800, but faster and better.  ;-)  And
the evolution of the 6502 into the 65xxx family is a pretty
straightforward "extension" of everything 8-bit to 16-bit and
everything 16-bit to 24-bit.  Not a lot of creativity, but a good
deal of "mess" from keeping all the past around, as usual.
Of course, being able to linearly address up to 16MB is a 
huge win over 64KB.

Perhaps the most significant difference between Motorola and
Intel processors is in the way that memory is addressed.  The
68xxx processor line offers linear addressing, meaning that all
addressible memory can be named by counting up an address,
without discontinuities.  On the other hand, x86 processors use
segmented addressing, in which a pointer can only directly address
a limited segment of the address space, and another "segment"
register must be changed to move to another segment.  This model
finally gave way with the 386, which offfered support for linear
addressing, as well.  But the difference created very different views
of software creation on the two different processors, some of which
persist to this day.  Needless to say, programmers are not overly
fond of segments.  ;-)

-michael

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