Yes, I did early development on both. At least the interface to the OS was 
Pascal.   I still have the early documentation buried in a box somewhere.

Sent from my iPhone

> On Jun 20, 2026, at 2:02 PM, Fred Cisin via cctalk <[email protected]> 
> wrote:
> 
> On Sat, 20 Jun 2026, ben via cctalk wrote:
>> PL/1 and C are the only two high level languages a operating system is 
>> written in, that I can think of that are well documented, and easily found 
>> on the WEB.
> 
> I heard that all of the Lisa OS, and much of Macintosh, were written in 
> Pascal. (obviously other than some low-level drivers and performance critical 
> routines?)
> Is that correct?
> 
> http://pascal.hansotten.com/apple-lisa-pascal/
> 
> When did Macintosh development switch to C?
> 
> --
> Grumpy Ol' Fred             [email protected]

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