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HD20 Question(s)

gavo

Well-known member
Hi,

I originally posted this over at the Vintage Macs google group but didnt get a response and someone pointed out this board so I thought I'd try my luck here :)

Anyway, from what I can see on the web, the reports are that the HD20 wouldnt work on a 128k mac due to memory limitations. Does anyone know if there was any way to get the HD20 to work on a 128k mac? Also, from what I have read, the HD20 INIT basically loaded HFS support along

with boot strapping the HD20, was it possible to use the HD20 with a MFS file system? If so, would this configuration work on a 128k mac?

Also, seeing as I dont actually have a HD20 (but do have a 128k Mac) - has anyone come up with an emulated HD20 - I see there is at least 1 emulated widget drive for the Lisa, and a couple of options on the Apple II using CF or IDE drives. Failing that, does anyone know the interface/protocol details for the interaction between the mac and the HD20 - and in fact, is this the same as for an external floppy drive (i.e. does the HD20 just look like a big fat floppy disk that cant be ejected?).

Cheers,

 

Big Bird

Well-known member
The 128K and 512K both use the original 64K ROMs that are incompatible with the HD20 and HFS partitions. On the 512K, the HD20 INIT enabled the use of the HD20, 800K floppy disks, and HFS partitions. You are correct that it will not work with the Mac 128K because it simply does not have the memory capacity unless it has been upgraded to 512K of RAM. Pina does say it is also possible to transplant Plus ROMs into the Mac 128K to enable it to access the HD20 without the use of the incompatible HD20 INIT. The 128K ROMs in the 512Ke, Plus, SE, Classic, Portable, and IIci all have HD20 and HFS support in the ROM, while later Macs will NOT support it, regardless of whether or not the HD20 INIT is installed. (There was a utility that allowed the SE/30 and possibly other Macs read-only access to data on an HD20, but it was officially unsupported by Apple: see the technote here.)

The larger capacity of the HD20 made it incompatible with MFS, and the way the HD20 INIT always loads HFS support, so unless you somehow hack the init, there's no way to "force" the HD20 to use an MFS file system. Apple only supported MFS on single-sided 400K disks. In systems prior to 3.0, 400K disks were formatted as MFS by default; in the early versions of System 7 (prior to 7.5), 400K disks formatted as HFS, but it was possible to force a single-sided disk to format as MFS by holding down the option key throughout the formatting process (until the formatting is complete). Support for the creation of MFS volumes was removed entirely from System 7.5, write access was disabled in System 7.6.1, and support for MFS volumes was removed altogether in Mac OS 8.

I don't have an HD20 myself, but I know a couple of people on the boards have posted pictures of their drives. I haven't taken the time to study the pictures, but my understanding is the drive used a specialized Rodime mechanism that did essentially allow it to be seen by the Mac as a giant floppy drive. Hopefully someone with one of these drives can contribute more information about the interface.

 

equill

Well-known member
Search this Forum with JDW and HD20 (poster and suject), and you will get plenty. JDW has probably contributed most about the matter, and some excellent pics.

de

 

JDW

Well-known member
I've "read" that the HD20 cannot boot a Mac 128k, and it theoretically makes sense why, but I've yet to read an article say: "Yes, I've tested and confirmed that the HD20 will NOT boot a Mac128k with or without the HD20 init, with or without 128k ROMs." The reason I mention this is because I've seen quite a lot of mistakes reported on the web about what will and will not work on old Macs. The best thing to do is test it yourself, I say. And to do that properly, you would need to use a variety of different OS versions, because some may work while others not. I've found this to be true of getting the HD20 to work on my Mac512. I can run up to Finder version 6.0 on it (using a System 4.x or 5.x), but 6.0.5 or 6.0.8 won't boot at all.

I don't know about the protocol used between the HD20 and the Mac. But since you mention MFS, perhaps this ADC TechNote may be of interest.

Since MFS supports drives up to 20 megabytes in size and a maximum of 1,400 files, it theoretically should work on an HD20. The reason why Apple prevents you from formatting the HD20 with MFS by default is due to the fact that MFS is a flat file system. Folders are nothing more than an illusion, thus making file management a real mess even on a drive as small as the HD20. So imagine an HD20 with a thousand files on it, and imagine you have those files organized into MFS's 'fake' folders. When you pull up the Open/Save dialog in a given app, ALL your files will appear in a single list (no folders)! But with HFS, you will see folders in the Open/Save dialog.

Nevertheless, there are times you may want MFS on an HD20 for compatibility reasons. In this case, paritioning the drive and formatting one partition as MFS makes the most sense. This Nested Volume Manager article has some interesting details on how one may wish to go about doing that.

It is also possible to format 400k floppies as HFS and 800k disks as MFS using some interesting tricks. Here is the trick to format 400k disks as HFS:

* Boot with a disk that has Finder 5.x or 6.x.

* Format/Initialize the 400k floppy while holding down the Option key and clicking One-Sided or Initialize.

  Or if the disk is in a 400K disk drive, hold the

  Option key down while you press the Return

  key after you've named it.

* If you want to duplicate an HFS 400k disk in the Finder (version 5.2 or higher) to another 400k disk while keep it HFS, you need to hold down the Option key during the process.

I have confirmed this on my Mac512. You must select the disk, then hold down OPTION, and then choose Erase from the Special menu. If your 400k disk is in the internal 400k drive, the dialog that appears will give you an "Initialize" button -- clicking that will give you an HFS 400k disk. And if your 400k disk is in an 800k external drive, the dialog will give you a choice of one-sided or two-sided -- clicking one-sided will create a 400k HFS disk.

I have also confirmed that these HFS 400k disks will not boot any Mac with 64k ROMs, neither in the 400k internal drive nor an A9M0106 external 800k drive. But that makes logical sense seeing the 64k ROMs cannot understand HFS without the HD20 INIT having been loaded first.

I've also "read" on the net that it is just as easy to make an 800k disk MFS:

* Format/initialize your 800k disk with any System/Finder you like.

* Boot with a disk that has an older Finder, like version 4.1

* Select your formatted 800k disk and choose "Erase" from the Special menu.

* And if you want it to be a boot disk, just use Finder 4.1 and an older System.

However, in my own testing, I have never been able to create an MFS 800k disk on a Mac512 with 64k ROMs! So unless someone can show me the steps to the contrary, I must assume this information is either bogus or it only applies to machines that have 128k ROMs. And it makes logical sense why it wouldn't work on a 64k ROM Mac. Look at the steps... The first step says to format the 800k floppy with any System/Finder. In other words, it will be formatted an HFS 800k disk (clearly, you would have loaded the HD20 INIT in order to do this on your 64k ROM Mac). If you then boot with an older System, even version 4.1, without loading the HD20 INIT, the 800k disk is not recognized and you will be asked to Initialize it! And yes, I've tried the 400k HFS steps on 800k disks -- doesn't work. Even if you load the HD20 INIT and hold down the OPTION key during the 800k floppy 2-sided initialization process, it will not be MFS!

At this point, you are likely wondering how to find out if a disk is MFS or HFS! That's easy. Just open a Finder window on the disk in question. Examine the upper left corner. You will see the square Close Box in the Title Bar, and just under that is the information bar (showing the number of items in the window and amount of disk space taken up). And just beneath that you will see two horizontal lines very close to eachother. In between those two lines, at the far left of the window, you may say a single pixel inside. If you do, the disk is HFS. If no pixel, it's MFS. You can spot that single pixel in each of the 3 windows shown in this screen shot.

Here are some HD20 photos, with a little commentary on some of them. I use the HD20 with a Mac512 that has the original 64k ROMs. I also have another Mac512 with a HyperDrive 20 (which is a lot faster than the HD20, by the way). I recently connected my HD20 to the HyperDrive Mac in hopes of easily swapping files from hard drive to hard drive. But for some reason the HD20 wouldn't mount on the HyperDrive Mac. The HyperDrive Mac does have a controller snapped onto the CPU, so perhaps that is the cause of the conflict. Hmmm. Anyway, my HyperDrive is formatted MFS and HFS. The HyperDrive creates partitions (called "drawers"), which makes MFS possible, I think. It's also interesting to note that the boot partition/drawer must be MFS on the HyperDrive, as described in this article (pull up that web page and search for "MFS" to jump to the right spot).

Here is a comprehensive listing of HFS & MFS technical notes (mostly from the mid-1980's) that are sure to give you hours of enjoyment!

 
Last edited by a moderator:

macdownunder

Well-known member
but I've yet to read an article say: "Yes, I've tested and confirmed that the HD20 will NOT boot a Mac128k with or without the HD20 init, with or without 128k ROMs."
I've not posted my test data, as I did this a long time before I found this forum, however I did an extensive amount of work trying to get the HD20 to work with a Mac128k and basically never found a combination that works.

From memory, the early small MacOS kernels (ie small enough to fit both kernel and HD INIT in memory) do not load the HD INIT. The smallest kernel I found that would load it on a Mac512 would not fit on a 128k.

I would have to get my machines out and retrace my steps to confirm which version did what, but I'm confident of my memory of the outcome - ie Mac128 won't work with HD20.

I certainly have a Mac512 with the 64k ROMs working with a HD20 and the Mac512KE booting from an HD20.

Regards,

Macdownunder

 

gavo

Well-known member
Thanks everyone,

Some really good info in there (and some good bedtime reading). Now if only I could find a HD20 to experiment with :)

Cheers,

 

JDW

Well-known member
I did an extensive amount of work trying to get the HD20 to work with a Mac128k and basically never found a combination that works. ...the early small MacOS kernels (ie small enough to fit both kernel and HD INIT in memory) do not load the HD INIT. The smallest kernel I found that would load it on a Mac512 would not fit on a 128k.
Even so, it is still likely that if you bought an old Mac Plus and put its 128k ROMs into a Mac 128k motherboard, it just might work. The reason is because you would no longer need to load the INIT in that case due to the code of the INIT already being inside the 128k ROMs.

 

Mac128

Well-known member
I too have confirmed that a stock 128K will not work with the HD20 INIT. Pina says that the 128Ke (128K with 128K ROMs) works just fine. JDW is correct that it may in fact work since the 128K does not have to load the HFS & HD20 drivers into RAM. However, I posed this question to Phil Beesley over at http://www.VintageMacWorld.com (arguably the current expert on the HD20) and he suggested I think rightly so: "In theory, you could use a HD20 with a Mac 128; in practice, the experience will be horrible because the Finder will try to cache all of the directory information and use up all of the RAM. Even when using floppy disks with a small number of folders/files, I'd expect nasty crashes when the Finder or an application runs out of RAM."

As for formatting an 800K MFS disk on a 64K ROM Mac, it is definitely possible. JDW, I saw those instructions somewhere too, but it was after I discovered it on my own ... where was that link? In any event it was second nature to my 128K and 512K so I never thought to document the process. I thought it was just a matter of attaching a proper drive as Larry Pina first posits and it just worked. In fact that's how it works for me. I simply attached an A9M0106 external 800K drive to my stock 512K Mac. Then I started up with a 400K MFS disk. Then I inserted a blank 800K disk and was asked to initialize it. Once It had been initialized, I had an 800K MFS disk, confirmed by the lack of an extra pixel under an HFS system formated startup disk. I NEVER went through the extra steps of first formatting the disk with a system and finder. So I've done it and used it ... actually it was invaluable in using my MacTerminal file transfer tutorial. However, I will be the first to admit that I did not note the exact steps I took to accomplish it since I assumed there were no special steps other than I've stated. Rather than speculate and add to the confusion, as soon as I have time to set up my Macs, I will make this a priority to determine since you were unable to reproduce it with your 64K ROM.

 

JDW

Well-known member
I'd expect nasty crashes when the Finder or an application runs out of RAM."
Hmmm. While Beesley's comments are founded in logic and likely right, I am inclined to test his "expectations" myself, once I get my hands on both a 128k logic board and some Mac Plus 128k ROMs. Such testing would prove not only IF it crashes due to lack of memory, but also show exactly which conditions cause such crashing. Curiosity killed the cat!

As for formatting an 800K MFS disk on a 64K ROM Mac, it is definitely possible... as soon as I have time to set up my Macs, I will make this a priority to determine since you were unable to reproduce it with your 64K ROM.
Such will be an outstanding contribution to this thread. I look forward to reading your findings!

Thanks.

BTW, for those reading this post, I got too eager to post 400k/800k information in this thread, which is somewhat off topic. So I would like to now refer to you this thread, where I shall post any further updates.

 
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