Mac II ROM Interchangeability?

[Mac128]

I believe the SE/30, and IIx ROMs are identical.

Since the Mac II can be upgraded to FDHD, does that also upgrade it to the IIx ROM?

I know the SE/30 can use a IIfx and IIsi ROM. And I understand the SE FDHD and IIcx are otherwise identical at least in function.

So what ROMs are actually physically compatible with each other?

Could the original Mac II be upgraded with IIfx & IIsi ROMs?

Were IIcx & IIci ROMs physically compatible with the rest of the II series? How about the IIvi & IIvx?

If the SE/30 could use the IIfx & IIsi ROMs, could those Mac IIs use the SE/30 & IIx ROM (or are they only backward compatible)?

 

[LCGuy]

Yeah, as a part of the Mac II FDHD upgrade you do need IIx ROMs. I don't think the SWIM controller will fully function without it, as the Mac II ROMs most likely don't have the right drivers, same with the SE FDHD upgrade.

 

[equill]

As LCGuy relates, in addition to insertion of the replacememt ROM chips:

HI (342-0639) at C13

MED HI (342-0640) at C12

MED LO (342-0641) at E13

LO (342-0642) at E12

the IWM chip must be replaced with a SWIM, but you also need System 6.0.2 or higher lest the Macintosh II still mistake the high-density drive as an 800kB mechanism.

de

 

[Mac128]

you also need System 6.0.2 or higher lest the Macintosh II still mistake the high-density drive as an 800kB mechanism.

Yes I read that and was surprised considering the IIx debuted with 6.0.1. Interesting ... I wonder what the physical difference on the logicboard was that caused that incompatibility since the IIx is often called simply a II with a 68030.

Anyway, I do see there is a physical incompatibility ... while the ROMs of the II, IIx, SE/30, II FDHD, SE FDHD, IIcx, IIci, IIfx & IIsi are all software interchangeable, they are not the same same physical size. The SE FDHD and II FDHD are in essence IIx ROMs in a different physical configuration. I assume the IIx, SE/30, IIcx, IIci, IIfx & IIsi all use the exact same ROM SIMMs, whereas all the others use custom chips. Perhaps this is the reason the II FDHD requires 6.0.2, due to the different pin configuration from the SIMM to the chip? That or there are more differences between the II FDHD ROM software and that in the IIx ROM.

So I also see, no one was able to ever use a IIfx ROM on a stock Mac II. I have to therefore use the transitive property of equality to assume if a Mac II can use a IIx ROM, and a IIx can use a IIfx ROM, then the Mac II can use a IIfx ROM. This is further supported by the fact that the II has a 68020 CPU, but can use the ROM of that for a 68030 processor with no ill effects. Unless of course, there is more to the Mac II FDHD ROM than meets the eye.

 

[Charlieman]

I think that there is some confusion here.

The early Mac models have ROMs that are in a DIP package. Examples: 128K/512K, 512Ke/Plus, SE and SE FD/HD. Later Macs (SE/30 and IIfx) had ROMs on SIMM, whilst others (IIci) had ROMs soldered to the board with an unused ROM SIMM socket. The IIsi was available with soldered ROM and, more rarely, with ROM SIMM. IIcx ROM type, anyone?

From this photo, it looks like the Mac II uses DIPs (sorry, I don't have the motivation to crawl around my collection tonight):

http://upload.wikimedia.org/wikipedia/commons/8/8e/Macintosh_II_motherboard.jpg

Note the four socketed DIPs next to the SIMM sockets. We can assume that the IIx layout is similar, because the ROMs were sold as an official upgrade to Mac II owners. The upgrade was useful because it allowed the use of the FDHD floppy AND improved RAM SIMM compatibility in Bank A (you still need PAL SIMMs and a 68851 PMMU or 68030 accelerator).

Repackaging the SIMM ROM types in DIPs is no doubt achievable but you need a lot of motivation to try it. Trag knows about repackaging soldered ROMs as SIMMs from his work on the IIci SIMM for an SE/30.

 

[Mac128]

I think that there is some confusion here....Note the four socketed DIPs next to the SIMM sockets. We can assume that the IIx layout is similar, because the ROMs were sold as an official upgrade to Mac II owners. ...Repackaging the SIMM ROM types in DIPs is no doubt achievable but you need a lot of motivation to try it.

Not really ... I am more interested in the encoded software compatibility than the physical compatibility. Having said that, the IIx ROM was a SIMM. While it makes sense to us that the IIx should have used the same layout as the II, especially considering their plans to allow for an upgrade, they essentially did the same thing with the SE/30 & SE. For whatever reason they got a wild hair that the ROM's would work better as SIMMs than DIPs. Why on Earth they would have soldered the ROMs in place on any machine is beyond me – lord knows by that time they had gotten enough ROMs wrong the first time around ... perhaps that was a way to limit the Mac from being upgraded. The Portable had the configuration as well.

 

[porter]

Why on Earth they would have soldered the ROMs in place on any machine is beyond me

It's cheaper

lord knows by that time they had gotten enough ROMs wrong the first time around

Did they? The architecture was designed to support software patching.

 

[Unknown_K]

The IIx has been called a SE/30 stuck in a mac II case.

 

[porter]

The IIx has been called a SE/30 stuck in a mac II case.

Hm, where did the screen go?

Have you noticed how a Mac II case is exactly like the bottom half of the original LaserWriter?

 

[Mac128]

lord knows by that time they had gotten enough ROMs wrong the first time around

Did they? The architecture was designed to support software patching.

I guess they just revised the Mac Plus ROM twice because they had nothing better to spend their money on. The Mac II also had a ROM replacement for owners of some NuBus cards ... software patching cannot handle everything. If it could, the 512K could boot directly from an HD20.

 

[macgeek417]

software patching cannot handle everything. If it could, the 512K could boot directly from an HD20.

No it couldn't... it would have to boot from a floppy to patch the rom, then boot from the HD20

 

[trag]

Repackaging the SIMM ROM types in DIPs is no doubt achievable but you need a lot of motivation to try it. Trag knows about repackaging soldered ROMs as SIMMs from his work on the IIci SIMM for an SE/30.

The above is true for values of repackaging which are equal to desoldering the ROMs from a IIci, reading the code out to disk, and writing the code into different Flash chips which were then soldered onto Gamba's board.

I mention this because it was not a case of removing the ROM chips from the IIci board and then soldering the same chips to a SIMM. One might interpret repackaging that way.

As it turns out, the ROM downloading utility which one uses to get a ROM file for the various emulators delivers a ROM file which is identical to what I got from reading the actual ROM chips after removing them from the IIci.

So I could have saved some trouble, but we didn't know that for certain ahead of time.

 

[yuhong]

Perhaps this is the reason the II FDHD requires 6.0.2, due to the different pin configuration from the SIMM to the chip?

Nope, did you know that the original release of System 6 released back in April 1988 was buggy? 6.0.1 fixed a lot of bugs and was originally what was supposed to ship with the IIx (and of course the II FDHD) which required it, but then another bug was discovered at the last-minute that led to 6.0.2.