Re: ROM Question

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

Quadrajet1 <quadrajet1@aol.com> wrote:

> >ROM Question
> >
> >    Are an original Apple I's ROM and Apple II's (Not II+) ROM the EXACT
> >same.  The 6502 machine language is ALWAYS same.  Is it possible that
> >assembly language like monitor routine remain unmodified for I and II, but
> >it did make some modification for II+ and later.  Please advise.
> 
>    It is extremely, and highly doubtful they are the same.  For one thing, the
> Apple I didn't have any slots to address.  And the type and amount of RAM is
> different.  I am sure parts and pieces may be the same, but overall, I doubt
> it.

They are completely different.  I haven't seen an Apple 1 or its
firmware, but I have read descriptions of them.

The Apple 1 had a very small ROM which only contained a monitor (and
probably some display support routines, possibly cassette tape support
as well?).  To get Integer BASIC running on the machine, Woz had to use
the monitor and type in the machine code, loading it into RAM.

The monitor would not have been identical to that of the Apple II, but
it is possible that the user interface and command syntax was similar.

The version of Integer BASIC that had to be typed in was probably very
similar to the Apple II version, but not identical, due to differences
in the monitor entry points, display hardware, etc.

As for the 6502: since the Apple 1 came out early in the life cycle of
the 6502 processor, it is quite possible that it _wasn't_ the same as
the version of the chip used in the Apple ][, ][+ and //e.  A few
instructions were added to the 6502 after its original release, but I'd
have to do some hunting to find the details.

-- 
David Empson
dempson@actrix.gen.nz