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Should a 400k drive work in a Mac II or other non-compact Mac?

mg.man

Well-known member
I recently acquired a 512k Mac with an additional external drive.  Both drives were totally jammed, but thanks to the advice here and elsewhere, I have them freed up and accepting / ejecting disks.  I don't have the 512k recommissioned yet, so have tried them in my Mac II.  It sees the drives, but won't read or format.  I've tried System 6.0.8 and 7.x...  Is it possible to at least test these drives in a non-compact Mac?

 
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Dog Cow

Well-known member
The 400K drive won't work with a SWIM controller. There's an Apple Tech Note out there somewhere saying so, and I've verified it myself on an SE/30.

 

Crutch

Well-known member
That’s interesting - but an original Mac II doesn’t have a SWIM, though. So I don’t think that explains OP’s issue. 

 
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mg.man

Well-known member
Just to add, I also have a IIx, and the 400k drive behaves the same in both.  Both II(s) seem to communicate with the drive, they pop up the unrecognised disk dialogue, and you can step through to attempting to initialise/erase the disk... but that only results in some head movement and the disk being ejected.  :-(

 

Dog Cow

Well-known member
That’s interesting - but an original Mac II doesn’t have a SWIM, though. So I don’t think that explains OP’s issue. 
Sure, but there was an FDHD upgrade for the Mac II, and maybe mg.man's Mac II has been upgraded to a SuperDrive with SWIM.

 

Crutch

Well-known member
I didn’t really know about that Mac II FDHD upgrade. How did it work? They swapped out the IWM for a SWIM?

 
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mg.man

Well-known member
They swapped out the IWM for a SWIM?
I found the following elsewhere online...

"The official name for the upgrade was the M6051/C Macintosh II SuperDrive Upgrade Kit that included an internal SuperDrive (M0247) and the ROM/SWIM Kit (M0244)."

Also... here's the "IWM" (which is actually a SWIM) in my IIx...

20200628_180121.jpg

...and I also found the following in an Apple Service Guide...

20200628_182748.jpg

So it looks like my II has the original "IWM" and the IIx the "SWIM"... I guess I'll have to get the 512k going to figure out if there's any life in either drive... 

 

Franklinstein

Well-known member
As mentioned it was an official upgrade, replacing the ROMs and the IWM for a SWIM, usually replacing one of the floppy drives with an FDHD unit (complete with a sticker to go on the case) and leaving the other as an 800k.

They rearranged the acronym with the FDHD system: originally an Integrated Woz Machine, it became the Super Woz Integrated Machine. I guess it flowed better than SIWM would have.

 
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techknight

Well-known member
the 400K drive requires a PWM signal or other special signal from the IWM thats only generated in the 128/512/Plus. 

Newer machines are missing that signal. 

 

Crutch

Well-known member
Excellent, there’s the answer.  If indeed all it needs is a PWM on one of the pins, a fun and entirely useless project would be to build a little Arduino hack to enable use of a 400k drive with an SE or Mac II ...   :)  

 

Crutch

Well-known member
Yep here it is, Technical Introduction to the Macintosh Family p. 227:

”Note: On the older 400K disk drives, a buffer in RAM (actually the low-order bytes of words in the sound buffer) is read by the Analog Signal Generator (ASG) to generate a pulse-width modulated signal, like the sound signal, that controls the speed of the disk motor. This speed variation is responsible for the characteristic humming of the disk drive. The Macintosh Operating System uses this speed control to store more sectors of information in the tracks closer to the edge of the disk by running the disk motor at slower speeds. On the BOOK drives, the variable disk speed is automatically controlled by the disk drive hardware.”

https://vintageapple.org/macprogramming/pdf/Technical_Instroduction_To_The_Macintosh_Family_1987.pdf

 

cheesestraws

Well-known member
Note: On the older 400K disk drives, a buffer in RAM (actually the low-order bytes of words in the sound buffer) is read by the Analog Signal Generator (ASG) to generate a pulse-width modulated signal, like the sound signal, that controls the speed of the disk motor
every time I feel both guilty and proud at the same time of a hack, I think about the relationship between the sound system and the floppy drive for 400k discs, and I feel not-alone.

 

mg.man

Well-known member
Thanks all! ... I'm working on bringing the 512k (as well as my Plus, which recently expired!) back to life.  Once I have one working, I'll revisit these drives to see if I can get them working.  Appreciate all the valuable info!

...it became the Super Woz Integrated Machine
FYI... there seems to be some debate here... according to the wiki [https://en.wikipedia.org/wiki/Integrated_Woz_Machine], SWIM stood for the Sander-Wozniak Integrated Machine ... Personally, I like 'Super-' better...  ;-)

 

Franklinstein

Well-known member
I was told that SCSI stood for Small Computer Serial Interface at one point (its actually System, not Serial, not the least because it is an 8- or 16-bit parallel interface) so it wouldn't be the first time there was some confusion with an acronym.

I did read the 'Super' part in a book somewhere though, and it was also specifically the 'Woz' abbreviation, not Wozniak, so maybe the author was just making up something that sounded good. But then that Wiki page also says that Sander built the original single-chip IWM so I don't know why it wasn't always a SWIM in that case.

Anyway, if your pressure pads are missing, they're probably stuck in the drive mechanism somewhere and can likely be glued back in place (though I think they're mounted on a removable peg for easy replacement but I don't have one on hand to be sure). Failing that, a paper punch and a sheet of felt from your local crafts store will make a replacement in a pinch.

 

mg.man

Well-known member
Just to close the loop...  Thanks to @Damian Ward for letting me test out one of my 400k drives on his (working) 512k, I can confirm that the drive is recognised and reads a MFS diskette just fine.  I also tried the drive on a Classic II (which I'd re-capped for him), but it behaved just like it did on my II and IIx.  This seems to point to that requirement for a... 

...PWM signal or other special signal from the IWM that's only generated in the 128/512/Plus
A big thanks to everyone for sharing your experience!  Now that I know I have a working drive, I can work on getting my 512k up and running!  

 
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