Thread
Highest Version of System Software on Mac 512K & 512Ke
This is going to be differnt for each machine, but what is the highest system version you have ever gotten to run on a Mac 512K or 512Ke?
Since the 512K requires loading the HD20 INIT into RAM, that is going to reduce the amount of RAM available for the larger systems. However, theoretically, the 512K and Ke should be able to run up to the same system versions.
It seems like I have run System 6.0.7 on a 512K, but that may have been the 512Ke (or I may be imagining things). I know for a fact I have run 6.0.5 on the 512Ke and have the HD20 running 6.0.3 at them moment.
I believe no one has ever successfully gotten the 6.0.8 System up on a 512K or 512Ke.
Please limit this to STOCK configurations and give the results of your experiences.
Since the 512K requires loading the HD20 INIT into RAM, that is going to reduce the amount of RAM available for the larger systems. However, theoretically, the 512K and Ke should be able to run up to the same system versions.
It seems like I have run System 6.0.7 on a 512K, but that may have been the 512Ke (or I may be imagining things). I know for a fact I have run 6.0.5 on the 512Ke and have the HD20 running 6.0.3 at them moment.
I believe no one has ever successfully gotten the 6.0.8 System up on a 512K or 512Ke.
Please limit this to STOCK configurations and give the results of your experiences.
My original Macintosh has been upgraded to full 512ke status, with 512k of RAM, and the newer ROMs that allow use of 800k floppy drives. I can confirm that I have definitely run System 6.08 on it. System 7, however, will not boot, as it complains about a lack of RAM.
I have also run 6.0.8 on a stock 512Ke. Used MacPaint and Speedometer on it, both worked very well.
From Mackido
System 4.1, Finder 5.5 (System Software 2.01)
Released: April 1987
Size: 422k | Download
Mac users had just a month to enjoy a nice 1 digit version number of their Mac OS. System 4.1 was released the following month newly adapted for AppleShare 1.1. AppleShare 1.1 was needed to network the newly released Mac II, and an updated version of the Mac OS was needed to accommodate it. Another update due to new technology was the way the Finder handled large capacity drives (namely those larger than 32 MB). This System also excluded a model, the Mac 512k, since you needed 1 MB of RAM to run it. This was the last time Apple did that for a while though, since they would not exclude models from running a version of the Mac OS for over ten years later, with the introduction of Mac OS 7.6.
So obviously someone's information is wrong because according to this from 4.1 onwards you need 1 meg and some people here say they have run later versions on 512ke machines.
System 4.1, Finder 5.5 (System Software 2.01)
Released: April 1987
Size: 422k | Download
Mac users had just a month to enjoy a nice 1 digit version number of their Mac OS. System 4.1 was released the following month newly adapted for AppleShare 1.1. AppleShare 1.1 was needed to network the newly released Mac II, and an updated version of the Mac OS was needed to accommodate it. Another update due to new technology was the way the Finder handled large capacity drives (namely those larger than 32 MB). This System also excluded a model, the Mac 512k, since you needed 1 MB of RAM to run it. This was the last time Apple did that for a while though, since they would not exclude models from running a version of the Mac OS for over ten years later, with the introduction of Mac OS 7.6.
So obviously someone's information is wrong because according to this from 4.1 onwards you need 1 meg and some people here say they have run later versions on 512ke machines.
System 6 will NOT run on the stock 512k with 64k ROMs. I've spent several hours in the past trying and failed. So Mac128's memory is recalling the 512ke, not the original 512k.
But I can say that I can run Finder 6.0 along with System 4.1 just fine on my 512k. And actually, Finder 6 is more of a pleasure to run too, versus older Finders. But again, I've not been able to run System 6 along with Finder 6. And if memory serves me correctly, I was not able to run any Finder newer than 6.0 either.
But I can say that I can run Finder 6.0 along with System 4.1 just fine on my 512k. And actually, Finder 6 is more of a pleasure to run too, versus older Finders. But again, I've not been able to run System 6 along with Finder 6. And if memory serves me correctly, I was not able to run any Finder newer than 6.0 either.
The following was garnered from the mentioned sources a number of years ago. It reposes in a WriteNow file amongst my Classic Mode/OS 9.2.2 partition of this present iMac. The Forum's software makes a pig's ear of the tabular form of the data, but I'm sure that you can interpret it. 'Rec.' is to be read as the Mac model recommended. The column headers are Rec, System#, Finder#, 'System Software' #, File system, Released mo./year, Size (kB on Disk)
de
My 512Ke was an 'e' when I received it, but it happily boots into 6.0.8 from floppy, its HD 20, and I am sure, its 40MB Quantum SCSI HDD when I get around to providing the Mac with a fan also. It has 2MB of RAM.
de
I assume you mean you tried exhaustively by putting the HD 20 v.1.1 INIT in the System Folder as well?
I would trust your results over the Mac512K as I have rarely gotten much substantiative responses from gyounk, but these are his obervations with suggest it will run 6.0.8. http://www.mac512.com/macwebpages/qamac128.htm
I believe Charlieman has already discounted this and indeed confirms himself the 512K will not run System 6.0.x in his TCP/IP 512K article n which he also mentions the use of the HD20 INIT to overcome space limitations.
Apple's official position is that support for the HD 20 was dropped in System 6, presumably because no new Mac that required it was having the HD20 driver encoded into its ROM and therefore the corresponding system support was dropped as well. Oddly, the Macintosh Portable is listed as compatible in the Apple Guide to Hardware, which leads me to think all the SE-based 68000 Macs (including the Portable and Classic) retained the HD20 drivers in ROM. I found this link http://docs.info.apple.com/article.html?artnum=5712 which discusses an INIT I had not heard of before, required pre-System 6.0.4. It makes me wonder if the HD20 INIT is still required with System 6, whether the drivers are in ROM or not, as with the SE/30, which even with the HD20 INIT cannot reliably write to the drive. Perhaps all of these things are linked somehow?
However, if you tried it, then my memory is indeed flawed about the 512K!
Correct. My tests included the HD20 Init -- testing with and without it. I tried it with my Hard Disk 20 too, but System 6 just won't work with my 64k ROMs.
Now I don't mean to suggest your memory is bad, but I would suggest that you put the 64k ROMs back into your 512k Mac and give it another test. It is highly likely you will discover what I have -- System 6 just won't work on the 512.
Nevertheless, my tests were "in the past" as well. So to ensure my memory is absolutely correct, I will retest within the next 48 hours, ensuring my test floppy is HFS formatted and has the HD20 INIT (as suggested by the web page you mention).
Unless you just want to repeat past tests, I would wait until Charlieman weighs in. I believe Mac512's results are widely in question. It does seem to be asking a lot of a 512K to load 6.0.8 with or without an HD20 patch. Since I was not specifically testing for this, I may well have lost track of which board I had in the thing at the time, so I defer to more experienced heads.
Well, I will wait for Charlieman to offer his report within the next 48 hours then. 
In the meantime, I would like to mention that to format a 400k floppy as HFS you must do the following:
1) Be running Finder 5.x or 6.x.
2) Format your 400k floppy but hold down the OPTION key when you click one-sided.
But the bottom of this web page makes it clear that you cannot boot off an HFS 400k floppy in the Mac 512k with 64k ROMs (because the ROMs don't support HFS). And since the computer cannot read the HFS 400k disk, putting the HD20 INIT on that disk in an attempt to make it boot won't work. It won't work because the computer needs to be able to understand the format of the disk in order to read it. If the computer cannot read the disk, then the HD20 INIT cannot be loaded. Hence, you cannot boot off HFS formatted 400k disks on the stock Mac512. If you try it and it works, then you have a 512ke (with the 128k ROMs).
Here is my detailed HFS/MFS post on this subject.
So you can see why the information posted here is clearly misleading at best. And despite what that site says, you will be hard pressed to fit System 6 and Finder 6 on a 400k floppy, even after trashing all the CPs, extensions and purging all fonts from the System file.
By the way, I just tested System 4.2 and Finder 6.0 on an 800k HFS floppy. I first booted off an MFS 400k disk that had the HD20 INIT. I then put my 800k floppy in my external 800k drive (the drive being directly connected to the Mac512). Then in the Finder, I double-clicked TeachText on the 800k floppy, which then switched the Systems from the 400k disk to the 800k disk. I could then eject the 400k disk and there was no need to reinsert it.
So if I redo my past tests on the 512, it would be in like manner. Namely, I would boot off an MFS 400k disk that had an older system/finder and the HD20 INIT. I would then need to see if I can put System/Finder 6.0.x on an HFS 800k disk and see if control will be handed over when I double-click an app on that disk. Of course, I could also try an MFS 800k disk too, but I've not found a way to format an 800k floppy as MFS on my Mac512k with 64k ROMs, without resorting to a hack. (You must verify whether or not the disk is HFS by booting with an HFS aware system or the HD20 init. Only then can you see the single pixel in the Finder window that shows if a disk is HFS formatted. If you see the pixel in the Finder window, then your disk is HFS 800k, not MFS 800k).
But booting off an HFS 400k disk with System/Finder 6.0.x is impossible on a Mac512 with 64k ROMs.
UPDATE: I just formatted an 800k MFS floppy by booting off the "magic" MFS 400k System 2.0 and Finder 4.1 disk (that also has the HD20 init). I then copied the contents of my S4.2/F6.0 800k HFS floppy to my MFS 800k disk. I then double-clicked TeachText on the MFS 800k disk which in turn switched System/Finder control of the computer to that disk. I was then able to use my MFS 800k disk just fine. I then rebooted and tried booting off the MFS 800k floppy (which also has the HD20 init installed in the System Folder). After a few seconds, I got to the Welcome to Macintosh screen but then a System Error ID=12 appeared. For whatever reason, I cannot boot off this 800k MFS disk with System 4.2. I also deleted off the HD20 INIT on the MFS 800K disk and then tried booting off it again. Nope. Same ID=12 System Bomb at boot time. So clearly, if I cannot get a known-good S4.2/F6.0 combination to boot of an MFS 800k disk, I don't see how I can get a System 6.0.x MFS 800k disk to boot!
Another Update (and possibly the "final word" on the subject):
I continued to test with various Systems and Finders in my MFS 800k floppy. I found that the "magic" S2.0 and F4.1 combination works great to boot my Mac512 off this MFS 800k floppy. I confirmed this works great with or without the HD20 INIT. Ditto for S4.1 and Finder 6.0, with or without the HD20 INIT. I then copied S4.2 over S4.1 after confirming that S4.1/F6.0 boots, leaving all other System files as is, but then the machine did not boot. So this would seem to show that S4.1 is the limit when booting off an MFS 800k floppy (at least, when in conjunction with Finder 6.0).
I then grabbed my 6.0.7 800k HFS disk and copied the System Folder to my MFS 800k floppy. After that, I double-clicked an app on my MFS 800k disk and the app launched just fine, and System level control of the computer was handed over too the 800k MFS floppy at that point. But when I quit the app and before I got back to the Finder, I got a System Bomb, ID=2.
I then proceeded to boot off my System 6.0.7 MFS 800k floppy. I got to the Welcome to Macintosh screen but then I got the error shown in this photo. Hmmm.
I then made an 800k HFS disk from a System 6.0.5 image that I had stored on my SE/30 -- "System Tools" (1 of the 4 System 6.0.5 install disks). I then put that disk into my Mac512's 800k external drive and proceeded to copy the System Folder onto my MFS 800k floppy. After the copy was completed, I launched an app on the MFS 800k disk and the app launched. But when quitting the app I got the ID=02 System Bomb. I then tried booting off the 6.0.5 MFS 800k floppy, but just as it got to the Welcome to Macintosh box, the box went blank and then started flickering like mad, at which point my Mac512 locked up. I then booted off my 400k S4.1/F6.0 floppy and then inserted the HFS 800k System Tools 6.0.5 disk. I double-clicked the installer app, but after a few seconds my Mac512 threw up another ID=02 System Bomb dialog.
Never willing to give up, I then copied my known-good copy of System 4.2 into the System Folder of my MFS 800k 6.0.5 disk (replacing System file 6.0.5). All other files in the System Folder were left untouched. I then added the HD20 INIT. This time, it booted to Welcome to Macintosh without the flickering freeze, but a second later (about when the Finder is to load), I got the ID=02 bomb dialog (with the Welcome to Macintosh box still visible in the background).
Am I beat? Heck no. I then tested S4.3/F6.0 with and without the HD20 INIT on my MFS 800k floppy. Nope. I get an ID=12 bomb at boot time. I then tried the same S4.3 and F5.5. Nope. Same ID=12 bomb. But my S4.3 didn't come from a disk image, so perhaps my copy of S4.3 is bad? No way for me to know without having a known good disk image, so if someone would be so kind as to help me out in that regard, I am happy to retest with S4.3.
Finished, you ask? Never! I then proceeded to put S4.2 and F6.1.8 onto an MFS 400k floppy, in a System Folder. No other files were on the disk. At boot time though, I got an ID=12 System Bomb.
And so, as you can see, the best I can do is S4.2 and F6.0 when running off an MFS 400k or MFS 800k floppy. If Charlieman can do better on a stock 512, I would certainly like to hear how it's done!
Thoughts?
In the meantime, I would like to mention that to format a 400k floppy as HFS you must do the following:
1) Be running Finder 5.x or 6.x.
2) Format your 400k floppy but hold down the OPTION key when you click one-sided.
But the bottom of this web page makes it clear that you cannot boot off an HFS 400k floppy in the Mac 512k with 64k ROMs (because the ROMs don't support HFS). And since the computer cannot read the HFS 400k disk, putting the HD20 INIT on that disk in an attempt to make it boot won't work. It won't work because the computer needs to be able to understand the format of the disk in order to read it. If the computer cannot read the disk, then the HD20 INIT cannot be loaded. Hence, you cannot boot off HFS formatted 400k disks on the stock Mac512. If you try it and it works, then you have a 512ke (with the 128k ROMs).
Here is my detailed HFS/MFS post on this subject.
So you can see why the information posted here is clearly misleading at best. And despite what that site says, you will be hard pressed to fit System 6 and Finder 6 on a 400k floppy, even after trashing all the CPs, extensions and purging all fonts from the System file.
By the way, I just tested System 4.2 and Finder 6.0 on an 800k HFS floppy. I first booted off an MFS 400k disk that had the HD20 INIT. I then put my 800k floppy in my external 800k drive (the drive being directly connected to the Mac512). Then in the Finder, I double-clicked TeachText on the 800k floppy, which then switched the Systems from the 400k disk to the 800k disk. I could then eject the 400k disk and there was no need to reinsert it.
So if I redo my past tests on the 512, it would be in like manner. Namely, I would boot off an MFS 400k disk that had an older system/finder and the HD20 INIT. I would then need to see if I can put System/Finder 6.0.x on an HFS 800k disk and see if control will be handed over when I double-click an app on that disk. Of course, I could also try an MFS 800k disk too, but I've not found a way to format an 800k floppy as MFS on my Mac512k with 64k ROMs, without resorting to a hack. (You must verify whether or not the disk is HFS by booting with an HFS aware system or the HD20 init. Only then can you see the single pixel in the Finder window that shows if a disk is HFS formatted. If you see the pixel in the Finder window, then your disk is HFS 800k, not MFS 800k).
But booting off an HFS 400k disk with System/Finder 6.0.x is impossible on a Mac512 with 64k ROMs.
UPDATE: I just formatted an 800k MFS floppy by booting off the "magic" MFS 400k System 2.0 and Finder 4.1 disk (that also has the HD20 init). I then copied the contents of my S4.2/F6.0 800k HFS floppy to my MFS 800k disk. I then double-clicked TeachText on the MFS 800k disk which in turn switched System/Finder control of the computer to that disk. I was then able to use my MFS 800k disk just fine. I then rebooted and tried booting off the MFS 800k floppy (which also has the HD20 init installed in the System Folder). After a few seconds, I got to the Welcome to Macintosh screen but then a System Error ID=12 appeared. For whatever reason, I cannot boot off this 800k MFS disk with System 4.2. I also deleted off the HD20 INIT on the MFS 800K disk and then tried booting off it again. Nope. Same ID=12 System Bomb at boot time. So clearly, if I cannot get a known-good S4.2/F6.0 combination to boot of an MFS 800k disk, I don't see how I can get a System 6.0.x MFS 800k disk to boot!
Another Update (and possibly the "final word" on the subject):
I continued to test with various Systems and Finders in my MFS 800k floppy. I found that the "magic" S2.0 and F4.1 combination works great to boot my Mac512 off this MFS 800k floppy. I confirmed this works great with or without the HD20 INIT. Ditto for S4.1 and Finder 6.0, with or without the HD20 INIT. I then copied S4.2 over S4.1 after confirming that S4.1/F6.0 boots, leaving all other System files as is, but then the machine did not boot. So this would seem to show that S4.1 is the limit when booting off an MFS 800k floppy (at least, when in conjunction with Finder 6.0).
I then grabbed my 6.0.7 800k HFS disk and copied the System Folder to my MFS 800k floppy. After that, I double-clicked an app on my MFS 800k disk and the app launched just fine, and System level control of the computer was handed over too the 800k MFS floppy at that point. But when I quit the app and before I got back to the Finder, I got a System Bomb, ID=2.
I then proceeded to boot off my System 6.0.7 MFS 800k floppy. I got to the Welcome to Macintosh screen but then I got the error shown in this photo. Hmmm.
I then made an 800k HFS disk from a System 6.0.5 image that I had stored on my SE/30 -- "System Tools" (1 of the 4 System 6.0.5 install disks). I then put that disk into my Mac512's 800k external drive and proceeded to copy the System Folder onto my MFS 800k floppy. After the copy was completed, I launched an app on the MFS 800k disk and the app launched. But when quitting the app I got the ID=02 System Bomb. I then tried booting off the 6.0.5 MFS 800k floppy, but just as it got to the Welcome to Macintosh box, the box went blank and then started flickering like mad, at which point my Mac512 locked up. I then booted off my 400k S4.1/F6.0 floppy and then inserted the HFS 800k System Tools 6.0.5 disk. I double-clicked the installer app, but after a few seconds my Mac512 threw up another ID=02 System Bomb dialog.
Never willing to give up, I then copied my known-good copy of System 4.2 into the System Folder of my MFS 800k 6.0.5 disk (replacing System file 6.0.5). All other files in the System Folder were left untouched. I then added the HD20 INIT. This time, it booted to Welcome to Macintosh without the flickering freeze, but a second later (about when the Finder is to load), I got the ID=02 bomb dialog (with the Welcome to Macintosh box still visible in the background).
Am I beat? Heck no. I then tested S4.3/F6.0 with and without the HD20 INIT on my MFS 800k floppy. Nope. I get an ID=12 bomb at boot time. I then tried the same S4.3 and F5.5. Nope. Same ID=12 bomb. But my S4.3 didn't come from a disk image, so perhaps my copy of S4.3 is bad? No way for me to know without having a known good disk image, so if someone would be so kind as to help me out in that regard, I am happy to retest with S4.3.
Finished, you ask? Never! I then proceeded to put S4.2 and F6.1.8 onto an MFS 400k floppy, in a System Folder. No other files were on the disk. At boot time though, I got an ID=12 System Bomb.
And so, as you can see, the best I can do is S4.2 and F6.0 when running off an MFS 400k or MFS 800k floppy. If Charlieman can do better on a stock 512, I would certainly like to hear how it's done!
Thoughts?
Thanks for waiting, guys. And thanks for all of the testing, JDW.
I don't have my notes from my past experiments, but I do have the 400KB disks that I used for testing System 6 on a stock 512K. With judicious editing, I was able to cut down System 6 so that it would fit on a 400KB MFS disk with the HD20 INIT. I used System 6.0.2 because it was the smallest stable version. Like JDW, I found that the Mac booted initially and then fell over.
For an explanation, this oldish thread gives some possible clues Mac Startup Sequence. My thoughts are that the Mac just boots without any checking of the disk format. In the case of a Mac with 64KB ROMs, the Mac bombs when booting System 6 because System 6 code assumes an HFS disk.
Perhaps there might be further clues in Inside Mac or contemporary TechNotes.
I don't have my notes from my past experiments, but I do have the 400KB disks that I used for testing System 6 on a stock 512K. With judicious editing, I was able to cut down System 6 so that it would fit on a 400KB MFS disk with the HD20 INIT. I used System 6.0.2 because it was the smallest stable version. Like JDW, I found that the Mac booted initially and then fell over.
For an explanation, this oldish thread gives some possible clues Mac Startup Sequence. My thoughts are that the Mac just boots without any checking of the disk format. In the case of a Mac with 64KB ROMs, the Mac bombs when booting System 6 because System 6 code assumes an HFS disk.
Perhaps there might be further clues in Inside Mac or contemporary TechNotes.
Here's another clue, relating to the use of HD20: http://docs.info.apple.com/article.html?artnum=4437
Now this refers to the 512Ke, which I know for a fact works with 6.0.3 off a HD20. There also appear to be other errors in the tech note (i.e. calling the 512Ke a Plus which can most certainly run 6.0.3 and the HD20), so perhaps they meant a 512K. However, if os it confirms 6.0.1 on it. If they did mean a 512Ke, then the Plus would suffer from the exact same issues as I believe they are architecturally identical with the exception of the SCSI bus and extra RAM mux.
Also, this may indicate differences which might have been dropped in System 6 as the 64K ROMs were no longer relevant: http://docs.info.apple.com/article.html?artnum=1778
If these are real limitations for the 512K, 512Ke & Plus, then there may be something to what Mac512 says and what JDW's test demonstrated ...
Given that the 512K is already saddled with the HD20 INIT and a 400K startup-handoff to the external System, perhaps System 6 must be treated the same way as an accepted limitation of its use, i.e as Charlieman suggests System 6 requires an HFS boot disk, looking into real directories not present on an MFS volume.
Of course there are practical considerations here as well ... even with the stock 512K running System 6.0.8, with extra RAM consigned to the RAM based HFS & drivers, how much useful software can actually be run on it?
Now this refers to the 512Ke, which I know for a fact works with 6.0.3 off a HD20. There also appear to be other errors in the tech note (i.e. calling the 512Ke a Plus which can most certainly run 6.0.3 and the HD20), so perhaps they meant a 512K. However, if os it confirms 6.0.1 on it. If they did mean a 512Ke, then the Plus would suffer from the exact same issues as I believe they are architecturally identical with the exception of the SCSI bus and extra RAM mux.
Also, this may indicate differences which might have been dropped in System 6 as the 64K ROMs were no longer relevant: http://docs.info.apple.com/article.html?artnum=1778
If these are real limitations for the 512K, 512Ke & Plus, then there may be something to what Mac512 says and what JDW's test demonstrated ...
...that the installer must configure a minimal system for the Mac Plus, from which any system reductions must be made. I have certainly run into situations where a particular system would not work if copied onto a Plus, but would if it were installed specifically for the Plus. This is the same reason the "Magic Disk" works – certain resources are copied into the system file which are not necessarily present in minimal startup copies not customized for specific hardware, like startup disks and tools.
Given that the 512K is already saddled with the HD20 INIT and a 400K startup-handoff to the external System, perhaps System 6 must be treated the same way as an accepted limitation of its use, i.e as Charlieman suggests System 6 requires an HFS boot disk, looking into real directories not present on an MFS volume.
Of course there are practical considerations here as well ... even with the stock 512K running System 6.0.8, with extra RAM consigned to the RAM based HFS & drivers, how much useful software can actually be run on it?
Well, I think that official Apple article says it all: System 6 is not supposed to be compatible even with the 512ke! It just so happens, per Mac128, that some flavors of System 6 do work on the 512ke.
Nevertheless, that same article also admits that 6.0.1 might work on the 512ke. So if someone wants to PM me with a working disk image of 6.0.1, I will give it a test. And even if you don't "want" to give me a copy, do it anyway for the sake of science! :beige: (Ditto for a System File 4.3 disk image that I request in my post above.)
Nevertheless, that same article also admits that 6.0.1 might work on the 512ke. So if someone wants to PM me with a working disk image of 6.0.1, I will give it a test. And even if you don't "want" to give me a copy, do it anyway for the sake of science! :beige: (Ditto for a System File 4.3 disk image that I request in my post above.)
Apple's database has a history of occasionally being wrong. They list the SE/30 as being discontinued in 1990, for example (it was made through October 1991, their own sales literature can confirm that).
I think what they mean to say is that they don't recommend running 6.0.x on a 512Ke. You can do it, just don't expect to run some high-end program with it. Something like MacPaint runs fine. I've tried both 6.0.5 and 6.0.8 on the 512Ke and both work. (So did 4.1).
Most books will back up this claim. I remember the Jim Heid/Peter Norton book from the late 1980s mentioning that a 512Ke can run System 6. I think Que's book on upgrading and repairing Macs also does. (My copy actually is completely duct-taped together since I've used it so much over the 13 years I've had it).
Don't believe everything you read on other sites either. So many have gotten the SE/30 date wrong it's not even funny.
I think what they mean to say is that they don't recommend running 6.0.x on a 512Ke. You can do it, just don't expect to run some high-end program with it. Something like MacPaint runs fine. I've tried both 6.0.5 and 6.0.8 on the 512Ke and both work. (So did 4.1).
Most books will back up this claim. I remember the Jim Heid/Peter Norton book from the late 1980s mentioning that a 512Ke can run System 6. I think Que's book on upgrading and repairing Macs also does. (My copy actually is completely duct-taped together since I've used it so much over the 13 years I've had it).
Don't believe everything you read on other sites either. So many have gotten the SE/30 date wrong it's not even funny.
Scott, I'd love to hear your tests on a stock 512k with 64k ROMs! I am not surprised to hear that 6 will run on a 512ke. My interest is in the 64k ROM Mac512.
Also, Scott, if you have System 6.0.1, would you might PMing me. I want to test that.
Also, Scott, if you have System 6.0.1, would you might PMing me. I want to test that.
If I had a 64K ROM 512K I'd test it.
I don't have 6.0.1...I have disks that are labeled as 6.0.1 but unfortunately it appears Apple stuck 6.0.2 on there instead. They came with a Plus.
I don't have 6.0.1...I have disks that are labeled as 6.0.1 but unfortunately it appears Apple stuck 6.0.2 on there instead. They came with a Plus.
A kind member of this site emailed me a disk image of System 6.0.1 today. Many thanks for your kindness in furthering science! 
Another great thing about the System 6.0.1 disk image sent to me is that the entire System Folder is under 400k. It was a snap to copy it to a freshly formatted MFS 400k floppy. I then tried to boot my Mac512 with it. However, I got the same error I reported in my post above, shown in this photo. It gets to the Welcome to Macintosh screen and then 3 seconds later it throws up the "Minimum" Installer Script error.
Does this mean it's simply missing a System Enabler? Or is it a meaningless error dialog that basically means "System 6 won't run on your 64k ROM Mac512"? If it is simply in need of an enabler, then how does one go about hacking that in via ResEdit?
NOTE: Technically speaking, System Enablers originated with System 7 and therefore do not apply to old compact Macs up through and including the plus. See Apple Tech articles: here & here.
Thanks.
Another great thing about the System 6.0.1 disk image sent to me is that the entire System Folder is under 400k. It was a snap to copy it to a freshly formatted MFS 400k floppy. I then tried to boot my Mac512 with it. However, I got the same error I reported in my post above, shown in this photo. It gets to the Welcome to Macintosh screen and then 3 seconds later it throws up the "Minimum" Installer Script error.
Does this mean it's simply missing a System Enabler? Or is it a meaningless error dialog that basically means "System 6 won't run on your 64k ROM Mac512"? If it is simply in need of an enabler, then how does one go about hacking that in via ResEdit?
NOTE: Technically speaking, System Enablers originated with System 7 and therefore do not apply to old compact Macs up through and including the plus. See Apple Tech articles: here & here.
Thanks.
JDW this goes back to what I was saying earlier. When I look at my 6.0.8 installer and select minimum system for Mac Plus it indicates that the system won't be able to run on any other Mac. Whether that means it adds something or doesn't include something is unknown. Sadly I don't have 6.0.1 install disks to check. But I can certainly check the differences In 6.0.8. If the minimal install for all Macs (which the version from disk tools you are almost certainly using, is) includes aspects of System 6 which are looking for hardware the 512K doesn't have or are incompatible with the HD20 INIT, then that might also account for the error you are getting.
Very true, Mac128. However, when I spoke of a "system enabler" in my previous post above, I was hinting at a hack similar to what we have for the SE/30 (i.e., changing a 003 to a 005 in ResEdit) that allows running of 7.6.1 and 8.1 on SE/30 hardware. True, you also need a IIsi or IIfx ROM in conjunction with the System file hack, but perhaps such a hardware mod would NOT be needed on a Mac512 in order to run 6.0.x? This is a question I therefore put forth to the community, especially you 68k programmers out there. Surely you would know what it would take, if even possible at all, to make System 6.0.x run on a stock 512 with 64k ROMs. But in the end, if there's no hope to get System 6 to run on the original 512, so be it. At least we tried! [] ]'>
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In order to boot at all, the HD20 INIT has to load into RAM at the appropriate moment during startup. If System 6 does not have any provision for this ROM patch, then I don't see how it could work and without it a 64K ROM Mac simply can't boot System 6 if it requires HFS to boot. Obviously System 6 can read and write MFS, but could the System really need HFS formatting to load the boot code?
I just did an interesting formatting on my Mac Plus by installing a minimum System 6.0.5 for Mac Plus onto a 400K HFS disk. Then I dragged the 400K HFS disk onto a freshly formatted 400K MFS disk. THe result was slightly different than I expected, it copied only the files onto the MFS disk and did not reformat to HFS. I then further dragged the system contents out of the folder so they clearly resided on the root directory (even though technically they were already there). It's interesting that the Mac knew to convert a real folder/directory into a fake folder grouping. Next I copied the HD20 INIT v.1.1 file onto the 400K MFS disk.
The 400K MFS disk will boot the Mac Plus, so to the extent System 6 needs HFS to boot, it's not in the formatting of the disk. Now to the 512K – no dice. It does pretty much what JDW reported: Happy Mac, to Welcome screen, but just about where I would normally see the HD20 loaded message, the screen freezes and the box begins to cycle. When I boot up with a regular pre-system 6 MFS HD20 boot disk and try to switch to the System 6 MFS disk, by launching an application from it, the application loads fine. Upon quitting, I too get an Error 2. The Application SystemVersion reports 6.0.5, but upon exiting reports error 2 as well. When I used an MFS 400K disk without the HD20 INIT, the exact same startup sequence occurred. That indicates to me that the HD20 is not a factor. In fact, as I suspect, the HD20 patch code is likely not even present in System 6, so despite the fact it is included on the disk, the System doesn't even know what to do with it – that, or it is hanging up at some point before it attempts to load the HD20 INIT. But what loads before the disk driver and HFS code? I suppose it is possible that System 6 attempts to load something from a 128K (and up) ROM before accessing any ROM patches for an unsupported 64K ROM.
Another interesting feature of this System 6.0.5 System ... the minimal system installed for the Mac Plus by default contains AppleTalk. It is possible that System 6 AppleTalk is somehow incompatible with the 64K ROMs, or loading before the HFS ROM patch can be loaded into RAM?
Either way, any effort to get System 6 to run on a 512K Mac would require a system hack which defeats the practicality of running System 6. Unlike the "Magic Disk" solution for formatting 800K MFS disks on a 512K Mac, getting System 6 to run does not seem to be a simple matter of installing the correct sequence of files. Both JDW's tests and mine suggest a much more serious hack is in order to get the System booting, or even running after booting off another disk and switching over to it. If one were limited to a stock 512K, it would seem that one could boot over to System 6 on an application by application basis in order to use a program that only runs on System 6. However, if upon exiting such applications the system must be restarted, it is not a very practical remedy.
I think Mac512.com MUST have been using a 512Ke and not realized it. The HD20 file makes no difference to a 512Ke and it seems to run System 6.0.8 without issue. Given that Apple does not recommend System 6 for a 512Ke, it is unlikely an installer would produce a custom install for anything below a Mac Plus. Therefore, if a standard install of Mac Plus software onto a 400K disk will not yield a bootable or even switchable System 6 disk, then there's not really much point. That said, I am certainly curious as to what is causing the actual limitations and will probably keep looking for a "hack" that demonstrates the removal of those limitations, but that is what it will be, not an easy workaround of standard software.
--
In looking at these Apple docs, it would appear that despite the fact the SE/30 does not have a driver in its ROM, the HD20 INIT does not allow access. Apple further refers to a special INIT which allows the HD20 to be mounted by the SE/30 and files copied from, but not written to. http://docs.info.apple.com/article.html?artnum=6182
Since the SE/30 ONLY runs System 6, it would seem that System 6 is not able to implement the HD20 INIT ROM patch. If it could, then the fact the SE/30 does not have the driver in ROM should not be a factor in its ability to access it. As the driver is in the Portable/100's and Classic's ROM, System 6's limitations are irrelevant. Interestingly Apple created an NEW INIT for the SE/30, but ONLY to access the HD20, not utilize it, their recommendation is to copy the info to a new SCSI drive (yeah I'll bet!) ... but seriously, what would be the real technical limitation to running an HD20 on an SE/30? The IIcx & IIsi seems to suffer from the exact same problem as the SE/30, yet it is not mentioned on Apple's site. Nevertheless, the IIci does have the HD20 driver in ROM and is otherwise identical to the SE/30 & IIcx/si. So the SE/30 INIT should work on the IIcx & IIsi as well and if the Classic II doesn't have the driver in it's ROM as well, then it would likely work on it too. But would it work on the 512K?
MORE IMPORTANTLY, Where is this INIT today? Is it included on an SE/30 disk set? I have looked all over the internet and found no other references to it.
I just did an interesting formatting on my Mac Plus by installing a minimum System 6.0.5 for Mac Plus onto a 400K HFS disk. Then I dragged the 400K HFS disk onto a freshly formatted 400K MFS disk. THe result was slightly different than I expected, it copied only the files onto the MFS disk and did not reformat to HFS. I then further dragged the system contents out of the folder so they clearly resided on the root directory (even though technically they were already there). It's interesting that the Mac knew to convert a real folder/directory into a fake folder grouping. Next I copied the HD20 INIT v.1.1 file onto the 400K MFS disk.
The 400K MFS disk will boot the Mac Plus, so to the extent System 6 needs HFS to boot, it's not in the formatting of the disk. Now to the 512K – no dice. It does pretty much what JDW reported: Happy Mac, to Welcome screen, but just about where I would normally see the HD20 loaded message, the screen freezes and the box begins to cycle. When I boot up with a regular pre-system 6 MFS HD20 boot disk and try to switch to the System 6 MFS disk, by launching an application from it, the application loads fine. Upon quitting, I too get an Error 2. The Application SystemVersion reports 6.0.5, but upon exiting reports error 2 as well. When I used an MFS 400K disk without the HD20 INIT, the exact same startup sequence occurred. That indicates to me that the HD20 is not a factor. In fact, as I suspect, the HD20 patch code is likely not even present in System 6, so despite the fact it is included on the disk, the System doesn't even know what to do with it – that, or it is hanging up at some point before it attempts to load the HD20 INIT. But what loads before the disk driver and HFS code? I suppose it is possible that System 6 attempts to load something from a 128K (and up) ROM before accessing any ROM patches for an unsupported 64K ROM.
Another interesting feature of this System 6.0.5 System ... the minimal system installed for the Mac Plus by default contains AppleTalk. It is possible that System 6 AppleTalk is somehow incompatible with the 64K ROMs, or loading before the HFS ROM patch can be loaded into RAM?
Either way, any effort to get System 6 to run on a 512K Mac would require a system hack which defeats the practicality of running System 6. Unlike the "Magic Disk" solution for formatting 800K MFS disks on a 512K Mac, getting System 6 to run does not seem to be a simple matter of installing the correct sequence of files. Both JDW's tests and mine suggest a much more serious hack is in order to get the System booting, or even running after booting off another disk and switching over to it. If one were limited to a stock 512K, it would seem that one could boot over to System 6 on an application by application basis in order to use a program that only runs on System 6. However, if upon exiting such applications the system must be restarted, it is not a very practical remedy.
I think Mac512.com MUST have been using a 512Ke and not realized it. The HD20 file makes no difference to a 512Ke and it seems to run System 6.0.8 without issue. Given that Apple does not recommend System 6 for a 512Ke, it is unlikely an installer would produce a custom install for anything below a Mac Plus. Therefore, if a standard install of Mac Plus software onto a 400K disk will not yield a bootable or even switchable System 6 disk, then there's not really much point. That said, I am certainly curious as to what is causing the actual limitations and will probably keep looking for a "hack" that demonstrates the removal of those limitations, but that is what it will be, not an easy workaround of standard software.
--
In looking at these Apple docs, it would appear that despite the fact the SE/30 does not have a driver in its ROM, the HD20 INIT does not allow access. Apple further refers to a special INIT which allows the HD20 to be mounted by the SE/30 and files copied from, but not written to. http://docs.info.apple.com/article.html?artnum=6182
Since the SE/30 ONLY runs System 6, it would seem that System 6 is not able to implement the HD20 INIT ROM patch. If it could, then the fact the SE/30 does not have the driver in ROM should not be a factor in its ability to access it. As the driver is in the Portable/100's and Classic's ROM, System 6's limitations are irrelevant. Interestingly Apple created an NEW INIT for the SE/30, but ONLY to access the HD20, not utilize it, their recommendation is to copy the info to a new SCSI drive (yeah I'll bet!) ... but seriously, what would be the real technical limitation to running an HD20 on an SE/30? The IIcx & IIsi seems to suffer from the exact same problem as the SE/30, yet it is not mentioned on Apple's site. Nevertheless, the IIci does have the HD20 driver in ROM and is otherwise identical to the SE/30 & IIcx/si. So the SE/30 INIT should work on the IIcx & IIsi as well and if the Classic II doesn't have the driver in it's ROM as well, then it would likely work on it too. But would it work on the 512K?
MORE IMPORTANTLY, Where is this INIT today? Is it included on an SE/30 disk set? I have looked all over the internet and found no other references to it.
I've been begging for someone to post that for ages. If any of you out there have access to that magical INIT, please PM me! I wish to test and offer the classic Mac community a complete report.
Thanks!
By the way, the minimum OS for the SE/30 is 6.0.5. The maximum compatible OS is System 7.5.5. (And with a IIsi or IIfx ROM and a System File hack, you can run 7.6.1 and 8.1.)
UPDATE: This Apple article makes it clear that 6.0.3 can boot an SE/30.
Here's a curious entry:
Since the Mac II was released with System 4.x, if this INIT was compatible with it, then it has less to do with a System 6 workaround than patching into ROM at a different location than the HD20 INIT, possibly patching drivers only and NOT HFS since the II series did not need HFS. Therefore, this driver will likely NOT work on a 512K assuming System 6 needs HFS awareness to function (and that is why SYstem 6 is not loading on a 512K). Is this the same driver as used in the SE/30? Probably. Since the SE/30 was based on the IIx, it would make sense. Clearly as long as the System software knows about and where to patch the INIT into ROM, then it will. This brings up a question about just how these INITs worked. Since the HD20 will not work with System 2.0, but will work with System 2.1, I assumed that System 2.1 provided a hole to load the HD20 INIT, by name or TYPE. Since the 512K will run System 5, clearly all versions of System 4.x have a hole for both the HD20 INIT and the MacIIHD20 INIT. Why the new driver then – did the new 68020/30 ROMs require different patch points? I would be curious to see if the old HD20 INIT would work on a Mac II running 4.x connected to a HD20 as described above. System 6, most certainly creates the proper hole. At the same time, it likely closed the original HD20 hole. Apple made the decision to officially drop support for the HD20 with System 6 and perhaps this is why, as there would have been little accommodation for it to support a 512K, even though many have indicated no problems with a 512Ke. I suspect RAM based HFS support would have had to be re-written with System 6, which doesn't make much sense for an obsolete product. As enticing as this INIT is, I seriously doubt whether it will solve this problem on a stock 512K if it's an HFS support issue. But it's always worth a try ...
If this analysis is correct, the real question is was the original patch hole for the HD20 INT closed System 6 arbitrarily, or was it due to an incompatibility? If the former, then the hack would be to make System 6 aware of the original HD20 patch point again. Since the 512Ke loads System 6 just fine and the only differences are an additional 64K in ROM, which is mostly HFS and SCSI drivers, what else could System 6 failure to boot be but the lack of HFS code? I know System 7 requires a SCSI disk and will not use an HD20, but could System 6 require the SCSI code to be present as a condition of startup (i.e. it expects the ROM to scan the SCSI bus and report back so System 6 hangs when the 64K ROM doesn't do this)?
And this from the Apple Developer's IIsi guide is just maddening:
Finally, the smoking gun. I found a read me text but alas no INIT off a developer CD:
Now that I've had a chance to sleep on this and reflect on what this means ... obviously somebody at Apple realized there was a need to get data off of an HD-20 by consumers who no longer had access to an older Mac or external SCSI drive. In an effort to keep them happy they offered this "temporary" driver (and ensured they didn't keep using that HD-20). However, the fact that it was first made available for the Mac II, may raise more questions than it answers:
Since the Mac II was released with System 4.x, if this INIT was compatible with it, then it has less to do with a System 6 workaround than patching into ROM at a different location than the HD20 INIT, possibly patching drivers only and NOT HFS since the II series did not need HFS. Therefore, this driver will likely NOT work on a 512K assuming System 6 needs HFS awareness to function (and that is why SYstem 6 is not loading on a 512K). Is this the same driver as used in the SE/30? Probably. Since the SE/30 was based on the IIx, it would make sense. Clearly as long as the System software knows about and where to patch the INIT into ROM, then it will. This brings up a question about just how these INITs worked. Since the HD20 will not work with System 2.0, but will work with System 2.1, I assumed that System 2.1 provided a hole to load the HD20 INIT, by name or TYPE. Since the 512K will run System 5, clearly all versions of System 4.x have a hole for both the HD20 INIT and the MacIIHD20 INIT. Why the new driver then – did the new 68020/30 ROMs require different patch points? I would be curious to see if the old HD20 INIT would work on a Mac II running 4.x connected to a HD20 as described above. System 6, most certainly creates the proper hole. At the same time, it likely closed the original HD20 hole. Apple made the decision to officially drop support for the HD20 with System 6 and perhaps this is why, as there would have been little accommodation for it to support a 512K, even though many have indicated no problems with a 512Ke. I suspect RAM based HFS support would have had to be re-written with System 6, which doesn't make much sense for an obsolete product. As enticing as this INIT is, I seriously doubt whether it will solve this problem on a stock 512K if it's an HFS support issue. But it's always worth a try ...
If this analysis is correct, the real question is was the original patch hole for the HD20 INT closed System 6 arbitrarily, or was it due to an incompatibility? If the former, then the hack would be to make System 6 aware of the original HD20 patch point again. Since the 512Ke loads System 6 just fine and the only differences are an additional 64K in ROM, which is mostly HFS and SCSI drivers, what else could System 6 failure to boot be but the lack of HFS code? I know System 7 requires a SCSI disk and will not use an HD20, but could System 6 require the SCSI code to be present as a condition of startup (i.e. it expects the ROM to scan the SCSI bus and report back so System 6 hangs when the 64K ROM doesn't do this)?
Anyone know what the exact file name is for that init? Is it named the same as the standard HD20 init, but a different version, or does it have its own special file name.
Hmmmm. Would it have been included on old developer disks? I have a pile of those I bought on Ebay.
Oooops. Never mind. I posted before I read the next post after that one.
I'd read the TIL article to which Mac128 refers too. All the documentation suggests that the HD20 transfer INIT is a temporary hack that you would not wish to be permanently installed.
My speculation is that the transfer INIT disables polling on the signal lines that are explicit to the SuperDrive IWM. So it provides enough functionality for a data transfer (ie a Finder copy) but other disk activity may require signals that are being disabled. Formatting a floppy disk is a case that the transfer INIT may not be able to handle.
BTW, Mac128, thanks for the test of a 400K MFS disk in a Plus. It destroyed my theory completely but it is good to know the facts.
My speculation is that the transfer INIT disables polling on the signal lines that are explicit to the SuperDrive IWM. So it provides enough functionality for a data transfer (ie a Finder copy) but other disk activity may require signals that are being disabled. Formatting a floppy disk is a case that the transfer INIT may not be able to handle.
BTW, Mac128, thanks for the test of a 400K MFS disk in a Plus. It destroyed my theory completely but it is good to know the facts.
It's also important to keep in mind that the highest System file version I could use to boot off an 800k MFS floppy is System 4.1. However, I can use version 4.2 on a 400k MFS floppy. Go figure!
Yes, in fact that would handily explain why they recommend you do not write to the drive. Perhaps what they've disabled affects not just formatting a floppy in the SuperDrive but writing to and attached floppy bus disk, including the HD20. Either way, I doubt this INIT would do much toward helping the 512K boot System 6. I fear the answer lies more in what's missing from the 64K ROM and the HD20 INIT, or the fact System 6 ignores the INIT altogether.
So what does the 128K ROM add that the 64K ROM doesn't have, that System 6 needs?
800K Driver – I booted the Plus off a 400K drive withe both the HFS & MFS version of System 6, so it doesn't need an 800K drive.
HFS – I booted the Plus off of an MFS disk. Are there resources in the System folder that are stored hierarchically so that HFS is actually needed to read them? Otherwise everything is at the root level and HFS shouldn't matter.
SCSI – Does System 6 require confirmation of the presence of SCSI or not ... a prelude to System 7's requirement of SCSI?
That's all I can think of? What else is missing that System 6 could possibly require?
To answer my own question I just took a look at Inside Macintosh IV and it turns out there could be any number of issues hanging System 6. The Sound, disk and serial drivers are stored in 64K ROM but not as resources. Also, the Apple Talk drivers were not in the 64K ROM. Since System 6 makes much more out of AppleTalk, that could be check it fails. It also makes reference to a number of QuickDraw bugs in the 64K ROM.
The reality of these facts is that System 6 may be expecting any number of things in the 128K ROM, no longer compensated for by dropping support for the 64K ROM, which the HD20 INIT never compensated for anyway and therefore System 6 will never be possible on a 512K without a custom INIT to load all of the 128K ROM code substitutions into RAM, the net effect being that there would be little usable RAM left for applications and therefore somewhat pointless.
Will that 800K MFS disk boot on a 128K+ ROM? Since Apple really shouldn't have expected anyone to be running 800K MFS partitions, there shouldn't be anything in the system folder to exclude it. Could you ResEdit compare the System files to see if there are any obvious differences? I can't imagine why 4.2 wouldn't boot off of an 800K MFS disk but boots fine on a 400K disk. Especially if 4.1 boots off an 800K MFS disk and I trust they are roughly the same size?
I will compare 4.2 and 4.1 with ResEdit when I have time after work, but I must admit I don't know what I am looking for, and there will be numerous differences.
As to the SE/30 INIT that allows the HD20 to be connected, I personally would still have use for it. I would use it to make easy backups of my HD20 via my SE/30. In this day and age, it doesn't make sense to use floppies for such backups, saving a 20MB hard disk to a modern drive is nothing! But alas, until I get a copy of that INIT, I cannot have this wonderful convenience!
Lastly, as I requested in one of my previous posts in this thread, if someone could be so kind as to send me a copy of System 4.3 on an original disk image, I would be grateful! The version I have didn't come from a disk image -- I found it on the web and it was simply compressed in a folder. I think it may have been corrupted, which is why that System file won't boot any disk on my Mac (400k or 800k) or any format (HFS or MFS).
As to the SE/30 INIT that allows the HD20 to be connected, I personally would still have use for it. I would use it to make easy backups of my HD20 via my SE/30. In this day and age, it doesn't make sense to use floppies for such backups, saving a 20MB hard disk to a modern drive is nothing! But alas, until I get a copy of that INIT, I cannot have this wonderful convenience!
Lastly, as I requested in one of my previous posts in this thread, if someone could be so kind as to send me a copy of System 4.3 on an original disk image, I would be grateful! The version I have didn't come from a disk image -- I found it on the web and it was simply compressed in a folder. I think it may have been corrupted, which is why that System file won't boot any disk on my Mac (400k or 800k) or any format (HFS or MFS).
Well spotted. It is more likely that the transfer INIT brain damages the 64KB ROM floppy interface rather than the 128KB+ ROM interface. The document talks about transferring data from an HD20 to other media. Given the era, this would imply that you could transfer data from the HD20 to a 1.4MB floppy disk.
This second theory is supported by the warning that external floppy drives should not be connected.
Me too, as they used to say in the AOL era.
A possible explanantion is the way that programmers work. When you are asked to modify existing code, you go back to the version that looks "cleanest". By cleanest, I mean the version that the programmer considers can support recently introduced features whilst being easy to update. You may review several versions of the code before making a choice. After making that choice, you might need to copy, paste and edit some code for existing features into your new version.
And it is during the copy and paste exercise that changes get missed. Perhaps the original programmer for System 4.1 was told to drop support for a feature that relied on a 64KB ROM. But when System 4.2 was being written, the programmer reverted to earlier code and incidentally included a discontinued feature.
This is pure speculation, but it is based on real life experience.
Actually that article was written contemporarily to the Mac II and specifically discusses the IWM. Another issue with that Mac is this hack has you basically connecting the HD-20 to an internal floppy disk. Meaning the Mac II had 2 internal enablers and no external ones. Since the HD-20 is being connected as an internal drive it is likely the Mac II ROM cannot support an additional floppy drive, particularly an external one, which is what the HD-20's internal IWM supports. Only the SE & Portable support two internal drives as well as an external drive. So at best, you could back up the HD-20 to the 1st 800K floppy disk. It specifically says what would happen of you try to write to the HD-20, which is: it will take a long time. It doesn't say not to do it, so I would think the internal floppy drive would be fair game as well. I must have gotten this article mixed up with the SE/30 one.
The SE/30 article specifically discusses transferring to the internal SCSI drive. The SWIM chip should support the HD-20, but it is being enabled via a hack and the SE/30 article also warns of writing to the HD-20, though it doesn't prohibit connecting an external floppy drive. Nevertheless who knows what affect this driver has on the floppy bus in general.
What is odd between the two articles is that the SE/30 uses the IIx ROM, derived from the II. This suggests the IIx ROM added support for an internal and one internal OR external floppy Superdrive if my theory is correct and would therefore have no problems supporting an external drive. However, there was no restriction towards writing to the HD-20 on the II, whereas on the SE/30 it's taboo. Is this because the HD-20 has it's own IWM chip onboard? Are SWIM & IWM chips incompatible at least with respect to this ROM patch? The HD-20 is endorsed for use by Apple on the Portable which also has a SWIM, but also supports the HD-20 natively in ROM.
Charlieman, you've raised more questions than you've answered!