The Apple IIGS Megahertz Myth – Userlandia

I just love this kind of thorough, well-researched digital archeology delving into the whys and hows of 70s and 80s computers. Having lived through that era as a fledgling teenage computer hobbyist when clock speeds were sub-megahertz and 4K of RAM seemed like an impossible amount of space to fill, we had no idea we were living in the Cambrian explosion of personal computing.

Every platform represented a unique branch in an evolutionary tree undergoing incredibly rapid evolutionary permutations. Each with their own clubs, offset-printed zines and software libraries, none compatible with the others. Few people outside some universities and corporations had ever touched a self-contained computer and no one in my family's extended social circles even had a computer at home! I remember it striking most people as simply being weird, prompting questions with a tone akin to "I heard you have a personal dirigible at your house. Um... what would you even do with that?"

No one knew what the future of computing would look like and we certainly never imagined that by the late 90s, the wild explosion of early diversity would have encountered an asteroid-scale die-off, shrinking to a single major survivor with a distant second place in household computers - leaving behind a landscape which felt shockingly empty compared to the wildly diverse frontier only a decade earlier.

Parts of this reminds me about an issue I had around the same time, I worked on porting A/UX the Unix port for the Mac II, we reportedly got half of the early production run, they came without plastics in cardboard boxes, with schematics and PAL equations (PALs were relatively new then) I found and they fixed a bug in the PAL equations (didn't handle 24-bit writes some new 68020 instructions could make) so I had some cred with them when we ran into a weird bug, very occasionally you worked with the IWM chip (used floppies) the keyboard would freeze up - but only on some machines.

Managed to figure out that the machines that worked had an ADB (keyboard) chip with markings on it, the ones that didn't had no markings - Apple swore they were the same, eventually told us the ones that didn't work were the ones the were doing the manufacturing run with ..... bug from hell ..... turns out there was some circuitry in there they were quite proud of, when you accessed the parallel IO (VIA) chip it tweaked the clock phase a little to give you faster access, part of working with the IWM chip involved setting up the timer in the VIA chip to time when the next sector would go by, we'd poll the timer fast enough to tweak the clock on every clock cycle resulting in the ADB chip which was connected to the VIA being clocked too fast .... we replaced that code with a simple delay loop

> Acorn did ship a computer with the 65816—the Acorn Communicator—but when Sophie Wilson visited WDC in 1983 and saw Mensch and crew laying out the 65816 by hand, it struck her: if this motley crew on a card table could design a CPU, so could Acorn. Thus Wilson and Steve Furber forged their own CPU: the Acorn RISC Machine.

I watched his YouTube video on this a few days ago. It goes WAAAAAY more in-depth than you'd expect and is a great hour of second-monitor viewing.

I still have my childhood IIGS. It sat in my folks’ poorly insulated attic for two decades before I rescued it, and it booted up on the first try! They don’t make ‘em like they used to.

Man, I wanted a IIGS so bad back in the day.

I remember our school computer lab had a whole bunch of Apple IIe's, a single Mac, and a single IIGS. The GS was by far the most coveted because (unlike most Macs of that era) it had a COLOUR screen and could play relatively advanced games. Eventually they upgraded to mostly Macs.

Dad ended up buying a 386 PC, which was probably for the best. Those SVGA graphics!

To me the most fascinating nugget of history was how close a young Tony Fadell (later General Magic, iPod, Nest) came to supplying high-speed 65816 chips!

This was a fascinating and ... detailed ... story. I appreciate that it went a little further into the history of Apple's involvement ARM than the recent spate of blog posts that didn't go back past Newton.

Intreresting point from one of the linked usenet posts

"Way back in '85, a 4MHz '816 cost noticably more than an 8MHz 68000."

( From Dave Haynie, https://groups.google.com/g/comp.sys.apple/c/RH1-BNz8x-c/m/3... )

I'll never forgive Apple for breaking their promise of "Apple ][ Forever." (https://www.youtube.com/watch?v=RHCp0nuA4xA)

I remember how a 1MHz 6502 easily smoked a 4MHz Z-80 back in the day. Apple could have followed on the II with at least a 2 MHz model.

I wonder at what other clocks did the WDC 65C02 support?

For reference, the Amiga 3000 with a Motorola 68030 @ 25 MHz arrived in 1990. The Atari TT @ 25 Mhz also arrived in 1990.

I love the mention of Mobius - I remember seeing a few caseless ones on folks’ desks when I was there in ‘88-‘90, and worked a bit with the OS designed for it, but there’s little concrete info about it on the web.

Love the story and MGS2 reference.