3" disks Was: InfoWorld - May 11, 1992 (3" disk formats)

Fred Cisin cisin at xenosoft.com
Mon Dec 2 16:26:54 CST 2019

Thank you.
I haven't heard from Brett Glass in decades, since he moved to Idaho.  He 
ran the numbers and decided that the differential in market value between 
his housing here and similar in Idaho was enough to support him for quite 
a while.  Since he was working as a writer, he didn't have to be 
physically close to his work, and he could get decent internet access 
through the university there.

3" drives were readily available in MFM compatible forms.  The drive was 
designed to be a drop-in replacement for 5.25" SA400 style drives. (OK, 
"SA450"?).  And the 3" drives even used a 34 pin card edge and a "molex" 
power connector (like 5.25"; unlike 3.5")
Depending of format choices, MFM from 180K to 720K.

Amstrad used them, as did early Gavilan and some others.  The Gavilans 
that I had (both 8 and 16 line models) were later ones, with 3.5" drives. 
Gavilan's MS-DOS 2.11 3.5" format was not the same as IBM's PC-DOS 3.20 
720K format.  But, some development continued, even after Gavilan 
collapsed, and the Gavilan MS-DOS 2.ll version K was the same format as 
IBM.  For those not familiar, MS-DOS 2.11 and 3.31 were versions that were 
heavily modified by OEMs, particularly for drive types (including >32M in 
3.31).  Hence, 2.11 and 3.31 are DIFFERENT from one OEM to another!

But, early on, AMDISK marketed two drive external boxes for Radio Shack 
Color Computer and for Apple2.  Coco was box standard SA400 compatible 

I never had one of the Apple2 3" boxes.  So, I have questions about the 
Q: Was it a different logic board on the 3" drive for compatability with 
the Apple2 "DISK2" interface?   (GCR encoding)
Q: Or did their external 2 drive box come with its own MFM FDC for the 
Apple2?   (In which case, like the SVA FDC, it could adapt an Apple2 to 
"standard" drive types)

I assume that the 2 drive external boxes came after the original drive as 
5.25" drop-in retrofit, but I could easily be wrong, and it is POSSIBLE 
that the Apple2 version could have been the first release of the drives.

The 3" drives were available in 40 and 80 cylinder models.
The 3" drives were available in single and double sided.  The single sided 
drives would permit "flippy" operation, to use the other side of the disk 
as if it were another disk.   BUT, the double sided drives (at least 
the few that I had) would NOT let you insert a flipped disk; therefore, 
the double sided drives could not access the "B" side of a "flippy" disk!
I never got around to looking into modifying the drive for that.

Grumpy Ol' Fred     		cisin at xenosoft.com

On Sun, 1 Dec 2019, Sellam Abraham via cctalk wrote:

> I thought this was fun; stumbled upon it while looking for what words of
> wisdom Fred had to share about the format of 3" disks:
> https://books.google.com/books?id=7D0EAAAAMBAJ&pg=PA86&lpg=PA86&dq=3%22+floppy+disk+format+fred+cisin&source=bl&ots=b3iHCeqJzB&sig=ACfU3U19DoXha-0sh2fqm26M72Z1tlKLXw&hl=en&sa=X&ved=2ahUKEwjsivXd75XmAhURLX0KHYL0BBkQ6AEwAnoECAoQAQ#v=onepage&q=3%22%20floppy%20disk%20format%20fred%20cisin&f=false
> Hopefully Fred will see this and tell me whether the 3" disk format was MFM
> or GCR given that the Orwellipedia says the 3" disk format was initially
> designed to work with the Apple ][ floppy drive interface.
> https://en.wikipedia.org/wiki/History_of_the_floppy_disk?fbclid=IwAR2atb2Z_j_-DVNLTT1eqAZLw4ajB9s0LxzWgSMQoyEoi0_5Yy1KuNi7_TI#The_3-inch_compact_floppy_disk
> Sellam

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