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How To Tell 64k ROMs from 128k (Plus) ROMs via IC Markings

Posted by: CC_333 on 2022-06-23 21:25:41

Here's what I've got for my 512k board:

Spoiler content hidden.

And, for comparison, here's the markings from what are definitely Plus ROMs (installed in a Plus board):

Spoiler content hidden.

They're obviously different, and I'm like 98% sure these are genuine 64k ROMs in this 512k board, but I want to see if I can remove that 2% of uncertainty so I know 100% what I have here.

c

Posted by: Crutch on 2022-06-24 04:43:13

I think just the copyright date is your answer. I am also only 99.9% certain of this, but I don’t see how there could ever have been a 128K ROM chip with an ’84 date on it (the Mac Plus was released in January 1986).

Posted by: cheesestraws on 2022-06-24 05:15:04

Agreed with @Crutch - but honestly, doing this from IC markings is really the hard way to do it. If I remember correctly, the easy way is to turn on the Mac and look at the border around the Welcome to Macintosh box: if it's a shadow box it's a 64k ROM and if it's a double-outline it's 128k ROM or higher

Posted by: CC_333 on 2022-06-24 11:26:44

@cheesestraws Agreed, but it's inconvenient for me at present to assemble it and boot it up, so I thought I'd try identifying it visually.

@Crutch Yes, it would seem that the copyright of '84 is an obvious clue. I just wanted to be sure.

Thanks!

c

Posted by: Crutch on 2022-06-25 04:46:41

Side note, the immediate decline in usage of the shadow-boxed WDEF variant (altDBoxProc, I think it was called?) after 1984 always struck me as a little sad. They looked quite nice!

Posted by: demik on 2022-06-25 04:50:31

342-0220-B and 342-0221-B are second revision of the 64k Mac ROM

Posted by: cheesestraws on 2022-06-25 06:14:47

Agreed, but it's inconvenient for me at present to assemble it and boot it up, so I thought I'd try identifying it visually.

Oh, sorry, for some reason I thought you'd taken it apart to look at the ROMs. I think I got your situation crossed in my head with someone else's. Ignore me, then!

Side note, the immediate decline in usage of the shadow-boxed WDEF variant (altDBoxProc, I think it was called?) after 1984 always struck me as a little sad. They looked quite nice!

I agree!

Posted by: CC_333 on 2022-06-25 11:35:35

Oh, sorry, for some reason I thought you'd taken it apart to look at the ROMs. I think I got your situation crossed in my head with someone else's. Ignore me, then!

No worries! I was kind of vague, so your confusion is understandable and mostly unavoidable on account of that!

342-0220-B and 342-0221-B are second revision of the 64k Mac ROM

OK, then. Looks like I've got my definitive answer!

Side note, the immediate decline in usage of the shadow-boxed WDEF variant (altDBoxProc, I think it was called?) after 1984 always struck me as a little sad. They looked quite nice!

I think so too!

I wonder if it would be possible to somehow modify the Plus ROM to draw that older variant of WDEF? That's assuming the routines to do it are sill there, of course, because re-adding them would be much harder than simply flipping a few bits around, I would think.

c

Posted by: Crutch on 2022-06-25 11:56:31

I wonder if it would be possible to somehow modify the Plus ROM to draw that older variant of WDEF? That's assuming the routines to do it are sill there, of course, because re-adding them would be much harder than simply flipping a few bits around, I would think.

It would! “Welcome to Macintosh” is drawn by the _SysError trap. My recollection is that _SysError doesn’t actually use the Window Manager (it draws a thing that looks exactly like a window, but is just drawn with QuickDraw) so it would probably be a fairly wonky _SysError patch to make this work. (If it used the Window Manager, we could just patch _NewWindow to replace whatever variant code it’s getting with the shadow box variant when it sees that it’s getting called from SysError, which would just be like a dozen lines of code.)

Posted by: cheesestraws on 2022-06-25 15:00:17

so it would probably be a fairly wonky _SysError patch to make this work

I may have fallen down a slight rabbit hole here but I draw the line at writing any code. At least in the version of the ROM that's around, it looks like one can specify a custom "deep shit draw proc", which is checked for here:

mac-rom/OS/StartMgr/StartAlert.a at 72f4af952310df94362d70d1e0259aef65ab814f · elliotnunn/mac-rom

Use https://github.com/elliotnunn/tbxi instead! Contribute to elliotnunn/mac-rom development by creating an account on GitHub.

github.com

And which is a low memory global:

mac-rom/ProcessMgr/Lomem.h at 72f4af952310df94362d70d1e0259aef65ab814f · elliotnunn/mac-rom

Use https://github.com/elliotnunn/tbxi instead! Contribute to elliotnunn/mac-rom development by creating an account on GitHub.

github.com

So if you could inject a value into here early enough (from the primary init code in a declrom perhaps?) ...

Posted by: Crutch on 2022-06-26 04:31:23

Nice! That global var isn’t documented that I know of. (Which is interesting because Inside Mac Volume II documents ridiculous detail about the System Error handler, including that DSAlertRect is a global variable one can change.)