DosFox2d ago

After watching the wonderful @mac84tv video on the MIMMS iNSPIRE exhibit, I noticed this early Macintosh ii prototype.

I have to admit I got *very* excited, as this is only the second Macintosh ii prototype I've seen. (YACCintosh and the Big Mac technically don't count, as they're a different architecture)

(Thanks to Mac84 for sending me a few more photos of the exhibit!)

Show threadDosFox2d ago

So this is almost definitely a Macintosh II as it has a socket for a 68020, 68851 MMU, and 68881 FPU.

It also has six 96 pin slots - likely NuBus.

As far as I'm aware, only the Macintosh ii prototypes had NuBus as the expansion. The other prototypes didn't!

Show threadDosFox2d ago

I probably need to actually annotate this board, but other indicators that this is a macintosh ii are the presence of a 8530 SCSI controller (granted this was also on the big mac, but shh!), two 6522 VIAs, socket for an IWM (next to two 20 pin headers), and a socket for an SCC.

There's also some surviving ICs for Appletalk - with a pair of mini DIN 8 connectors.

There's also a pair of mini din connectors that's likely for ADB.

Show threadsleet01
@DosFox I didn't realize there was a period when MMUs were external chips!
Apr 3 at 6:06pmWeb
Show threadDosFox2d ago

@sleet01 there was a period of time that the MMU was scratch built out of individual TTL ICs, with processors that weren't designed with MMUs in mind!

Take a look at the Lisa architecture. The MMU was built out of a bunch of TTL and SRAM for registers (!) bolted onto a 68000. It's great!