24 Jul
2020
24 Jul
'20
6:10 a.m.
On Jul 21, 2020, at 9:26 PM, Henry Bent <henry.r.bent(a)gmail.com> wrote:
That was always really funny to me. Your machine boots MacOS, presumably because it was
easier to let it deal with hardware initialization than to rewrite it
This is actually because the Mac OS is already in the middle of booting, because big
chunks of it were ROM-resident. The ROM didn't just exist as a bootstrap loader for
any OS; it was a subset of the OS that just loaded more of itself, replaced parts of
itself, etc.
This only ended with the adoption of Open Firmware by the "New World" PCI-based
Power Macintosh series. Even there, the second-stage bootstrap invoked by Open Firmware to
get Mac OS up and running was actually a file on disk named "Mac OS ROM."
-- Chris