MacSCSI by John Bass AT LAST!

[H3NRY]

The SCSI board is simple, and if you happen across a Micah internal SCSI hard drive kit which existed for both the Mac Plus and the Mac 128 / 512, you'll have essentially the Bass SCSI port. Micah's SCSI adapter added 2 ROM sockets so the DRVR could be present at boot, and a 64K ROM Mac could boot from its hard disk. Find a Fat Mac with a Micah Drive and you've got your ROM driver.

That said, if the criterion is non-destructive, build a Bass style SCSI card, plug it into the ROM sockets, and plug in a pair of Plus ROMs. That'll give you the code you need to access the SCSI port, and nothing needs to be soldered or otherwise messed with on your pristine 128K motherboard. The biggest hassle is feeding a SCSI ribbon cable out thru the battery compartment door, the floppy opening, or the security slot. If you're gonna do an internal drive, you're going to have to do some real hacking & drilling, add a power supply and a fan, so figure an external SCSI drive.

You can unplug everything and go back to bone stock. If the criterion is keeping the Mac 100% "original", then the whole idea of an internal SCSI / flash / HD / whatever is out, right? If your criterion of "original" is 64K ROMs, then you've got to persuade someone who knows 68K assembler and the 64K ROMs inside out to spend 3 man-months to write a driver for you, and that ain't gonna happen. It seems to me some are arguing that they want to turn an original 128K Mac into a Mac Plus but keep it original without turning it into a Plus. :?:

A 128K is so very limited by the tiny bit of RAM, it doesn't work very well with a hard disk. If you have an "Original 128K", then leave it alone. Admire it. Think how it's appreciating in value. Show it off to your friends. Just don't expect to do much more than draw pictures with MacPaint and write short documents with MacWrite.

 

[JDW]

It seems to me some are arguing that they want to turn an original 128K Mac into a Mac Plus but keep it original without turning it into a Plus. :?: =

I do have a stock 128k logic board myself with the original 64k ROMs, but I prefer to use a 512k logic board instead, since it too has the 64k ROMs plus enough RAM to be quite usable. I simply would like to have the best of both worlds. If there existed a driver for the 64k ROMs, then I perhaps I could track down a SCSI SSD which would eliminate the need for an internal fan and perhaps would be low power enough to not even warrant a secondary PSU.

If a 64k ROM compatible SCSI driver really is impractical to create, then it would be nice to have the means to switch between the 128k and 64k ROMs (via mechanical flip switch on the back). Yes, I know I could accomplish the same tasks I desire simply by having a Mac Plus sitting next to my Mac 512k, and I could just use the Plus when I needed SCSI access. But having a single machine that could do both would be better. It would take up less desk space. But most of all it simply would be impressive a single machine that could do that. It would still be "original" in a major way, plus it would have features that only a 512ke, Plus or higher have -- SCSI access.

As to that 3 months of hard coding work, I wouldn't necessarily rule that out. For truly, if I had experience with 68k assembler programming and if I were retired, I can tell you for a fact that would be on my list of fun projects to tackle. Not sure if I am alone in thinking that way, but I do know there are some on this list far older than myself who might be willing to give it a try, perhaps some day. Some may consider such a "waste of time." But then again, some people may consider our posting on a vintage computing site to also be a waste of time. Let's face it, we're sort of geeky. And this is one of those geeky, but not completely impossible, projects to dream about. It keeps the vintage computing enthusiasm alive and kicking.

 

[H3NRY]

If a 64k ROM compatible SCSI driver really is impractical to create, then it would be nice to have the means to switch between the 128k and 64k ROMs (via mechanical flip switch on the back).

That's do-able, too. Put two sets of ROM sockets on your SCSI adapter with a switch. A SCSI ROM isn't impossible, it's just a lot of work for a problem that's already been solved. Micah's ROMs were written by Steve Brecher, a real Mac Guru, and he spent six months refining and debugging them. I suppose I am missing something, but I don't see the allure of the 64K ROM. The 128K ROMs contain the same code and toolbox as the original with bug fixes, and also support HFS, SCSI, and the rudiments of AppleTalk, among other things, *and* they were written by the genuine Mac team. If you enjoy writing drivers, a SCSI driver for the original Mac is a fine way to spend your summer. I promise you'll learn a lot!

Has anyone else seen a Micah drive? It appears they are much more rare than HyperDrives. IMHO, they were a more elegant solution, since they didn't require a CPU clip, drilling holes in the chassis, pop rivets, etc.

 

[Mac128]

Put two sets of ROM sockets on your SCSI adapter with a switch.

Ah, it sounds so simple, but what exactly do you switch? I brought this up in another thread and it was suggested the ROMs could be stacked and the switch would toggle between a single pin that enabled the ROMs.

As that article suggests, I'd also like to switch between 128K & 512K as well. So one Mac would basically be a 128K, 512K, 512Ke and 512K-Plus in one box.

Has anyone else seen a Micah drive?

No but now that you've clued me onto it, I will keep my eyes peeled. But isn't the driver only for the Micah drive? It wouldn't work on any other SCSI drive, right?

 

[H3NRY]

The switch goes to the chip enable pins. I don't remember the pin number off hand, but if you're building a Bass adapter, it should be noted on the diagram. Micah's ROM should work with most early SCSI drives and a Bass-style adapter. The Micah HD used a SMS 3100 SCSI-to-MFM controller card and any of the 20 MB MFM drives of the day, NEC being the most reliable of the lot.

 

[trag]

Apparently there's some kind of hook in the original Mac's/Mac Plus ROMs
I ran into a guy at the Goodwill Computer Store years ago who programmed some of those old Mac products and we talked about it at length.

BTW, the guy I ran into at Goodwill all those years ago was H3NRY. I'm glad he's here now.

 

[demik]

After a long journey, I've finally located the fabled Dr. Dobb's articles written by John Bass detailing his SCSI solution for the original Macintosh 128K & 512K utilizing the original 64K ROM. I have published the PDF file at this link (Beware it is a 6MB file).

Anyone got the file above ? The link is just a frameset with the PDF on one frame, and the PDF itself is not found (Error 404)

 

[JDW]

Anyone got the file above ? The link is just a frameset with the PDF on one frame, and the PDF itself is not found (Error 404)

I don't know if there ever was a file.  If there was, I was stupid for not having downloaded it back in 2009 when this thread was started.  I spent a lot of time Googling for it recently but came up with nothing.  Hopefully someone can provide it.  I hate it when useful information resources like this are lost forever.

 

[Crutch]

@Dog Cow implies he has the info. https://macgui.com/news/article.php?t=471

He says it was in the Sep 85 Dr. Dobb’s and subsequent issues. Maybe try here?

https://archive.org/details/dr_dobbs_journal

 

[sfiera]

https://archive.org/details/dr_dobbs_journal_vol_10/page/n721/mode/2up ?

 

[JDW]

https://archive.org/details/dr_dobbs_journal_vol_10/page/n721/mode/2up ?

Nice find!

After reviewing that article, I took note that John Bass says his software really only handles drives up to 5MB, suggesting additional software to partition the drive if you go beyond 5MB to keep the sheer number of files from bogging down the system.