strangest systems I've sent email from

Chris Hanson cmhanson at
Fri Apr 29 12:14:13 CDT 2016

On Apr 29, 2016, at 7:16 AM, Fred Cisin <cisin at> wrote:

>>> And you do know what Apple MacOS was originally written in, don't you?
>> On Thu, 28 Apr 2016, Chris Hanson wrote:
>> The original Macintosh System Software was almost entirely M68000 assembly language.
>> There were a couple parts of the original System Software that were written in Pascal, but by and large the space constraints of the 64KB ROMs and the 400KB floppy and the desire to eke every last cycle of performance out of the 8MHz CPU led to pervasive use of assembly.
>> The APIs were defined in terms of both Pascal and assembly, which is what leads people to think that it was written in Pascal.
> How much was based on Lisa?  What was THAT written in?

Not much. I think the Memory Manager was originally written in Pascal for Lisa but got rewritten in 68K assembly for the Mac.

Lisa was designed to have 512KB to 1MB on a stock system, expandable to several MB, and also included an MMU & virtual memory. The original Lisa had two 860KB Twiggy drives and typically came with a ProFile, while the Lisa 2 included a 5MB or 10MB ProFile, so a Lisa system typically even had swap.

Most of the lower-level portions of the OS were written in Pascal. The Lisa Office System applications and the Desktop were written in Clascal, a Smalltalk-style OO enhancement to Pascal that Apple hired Wirth to help design, which later turned into Object Pascal. All of the applications were based on the Application Toolkit, a Clascal framework implemented as a system shared library, whose design was a direct predecessor to MacApp.

None of that would really fly on the Mac, with 64KB of ROM, 128KB of RAM, and a single Twiggy (later Sony 3.5in) floppy.

  -- Chris

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