Yesterday, I picked up an Apple IIgs!

Today, I opened it up and removed the battery, and discovered it's a ROM-00 machine. Sounds like there might be advantages to upgrading it to a ROM-01 but I'm not super into this circle yet.

Anyone with more experience have any insight?

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@vkc I'm just about to start covering the IIgs on the blog. So far it's only been referred to in development as the "IIx". 🙂

@vkc You absolutely want ROM 01, a lot of software (including GS OS after some point, which is what restricts many other packages) requires at least ROM 01. ROM 03 is not possible on a ROM 01 board, and there was no ROM 02.

The 00 to 01 upgrade is just a matter of writing an appropriate ROM and sticking it in the socket. Hang on to the 00 chip, though, most IIgs owners upgraded to 01, so there aren't a lot of those around!

@vkc As far as getting the ROM chip ... I'm not seeing one, which may be why the Apple II houses seem to be selling a SMT ROM on a carrier.

Digi-Key says they have a 28 pin 128kx8 DIP UV EPROM, but the data sheet they list for it is 32 pin, and it's coming from a third-party warehouse, so who knows.

@elb This is extremely helpful. I thought I read somewhere that ROM 01 can't be upgraded to ROM 03. Still figuring it out!

And yes, I'll plan on holding on to that ROM 00- who knows what adventures might require that chip!

@vkc Yes -- ROM 03 motherboards are different (in particular, I think the ROM 03 ROM is larger and requires more address lines, so it won't even read properly). That's fine, though, ROM 01 doesn't lose you almost anything (and vice-versa is also true, ROM 03 doesn't lose you almost anything). ROM 00, on the other hand, will. ;-)

You should be able to run ProDOS 8, ProDOS 16, and GS OS through I think 4, as well as a lot of older software on your ROM 00 machine as it is, though!


@vkc You likely already know this, but the first thing you should do is open it up and snip out the battery! It's readily replaceable with a socket that you can attach in the open space under the power supply (I bought some recently have a Digi-Key part number if you want), but it's a time bomb. It's on the left under the PSU, which has a clip in the front and lifts out.

There's also a bulk cap and a couple of RIFAs in the PSU that are on borrowed time. They're easy to replace.


@elb Absolutely the first thing I did was snip out that battery! I ordered a socketed battery replacement just before going to pick up the IIgs- I wasn't messing around with that. I've got a cap kit on the way as well.

I did come across this replacement ROM adapter, which I'm imagining I might want?

@vkc Great!

For the record, my ROM 01 IIgs has a hugely bulging bulk cap, but is ... still going. I have the replacement in a baggie sitting on top of it. ;-)

Yup, that one is fine, and there are a couple of others (ReactiveMicro, Garrett's Workshop, maybe GlitchWorks?), they should all be functionally equivalent, although not all of them will let you choose ROM versions like that one. I can't recommend (or discommend) any particular product.

@elb Super helpful info- thank you so much! I came across ReactiveMicro in my searching too, but it looked to be unavailable. This one from a2heaven looked more available, lets hope it works!

I'm just digging in to retro Apple fun of this vintage, but I used a IIgs like this a bunch as a kid in school, and it's fun getting to see what was going on inside it!

@vkc Haha, I now see that your opening post said you removed the battery!

It's endemic on retrocomputing enthusiasts, we see a battery, we snip. We hear that there might be battery, we recommend snipping. ;-)

BTW, if you have an Apple SCSI card (might be a tall ask, I know), you can use a Zip drive as a cheap & readily available external storage medium! The Apple SCSI driver disk has a partitioning utility that will partition it into three 32 MB ProDOS partitions + the leftover.

@elb @vkc Ethan has great advice. I got a ROM 03 mainly because I found some of the projects required it like HDMI and video adapters but THAT WAS YEARS AGO, so please don’t assume what I say is true now. The 03s also had more standard on-board RAM. The ROM 0 is the so-called “Woz” edition. It’s a nice collector’s item but definitely worth upgrading.

If you find a Mark Twain (the ROM 4), let us know. 😂 (Never released.)

@ultramagnus_tcv @vkc (Note that mine is a Woz with a ROM 01, possibly a later upgrade (I think Woz editions came both ways?), but there seem to be gajillions of Wozes out there if one would like one.)

There are definitely things that want/require ROM 03, and I think ROM 03 machines can accept more RAM (?), but in practice for retrocomputing purposes I don't think it matters that much either way. You lose a tiny few things on the fringes either way, but the bulk of IIgs software is indifferent.

@elb @vkc I remember at the time wanting an 03 because I was still on composite video and I wanted to get one of the available video options at the time. I can’t remember if it was Tulip House or something else. Either way, it required a 3. This was… maybe 2016. So it’s been awhile. 3s have been harder to come by but the 01 is quite fine. Still wouldn’t mind a 4. I did actually see a Mark Twain but sadly the person that had it died recently.

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