• Please review our updated Terms and Rules here

5 1/4” 720kb Floppy Drive Why? when? Where?

VERAULT

Veteran Member
Joined
Jan 30, 2012
Messages
6,207
Location
Connecticut, USA
Does anyone know what size and format the Twiggy 5.25" apple drives were? Ya know since they were the ONLY 5.25" floppy drive made by apple with 2 heads...
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
5,308
Location
Upper Triassic
Does anyone know what size and format the Twiggy 5.25" apple drives were? Ya know since they were the ONLY 5.25" floppy drive made by apple with 2 heads...
They used a bizarre format with 46 tracks (using a non-standard TPI of 62.5, vs the 48 or 96 of 40/80 track 5.25" disk drives) with between 15 and 22 sectors per track, for a total of about 870K. The media had a similar magnetic coercivity to 1.2MB high-density floppy disks, it wasn't the same formula as double density disks.
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
5,308
Location
Upper Triassic
It was okay, and it was ambitious when Apple initially sketched out the plans for "Twiggy" in the late 1970's, but when you consider how much overhead it entailed with the variable speed motor and whatnot it seems like a pretty expensive way to get only about 20% more space per side than a regular MFM controller could do on conventional 5.25" media in a 96/100 TPI drive. (Which themselves came out in the late 1970's.)

There was a reliability argument to be made for the idea of using different sector counts on the inner and outer tracks, it does make intuitive sense that a "longer" track should be able to hold more data than a "shorter" one if you implement some kind of mechanism to make the "bits" of uniform size, but changing the rotation speed of the disk is a pretty half-***ed way to do it. You can accomplish the same thing by implementing variable data rates in the controller, which is what Commodore did in their disk drives. A drive like Commodore's 8050 crams more data per side onto plain old DD media than a Twiggy or Macintosh drive using a mostly standard Micropolis disk mechanism with a fixed speed motor, with similar reliability(*), and it was available in 1980.

(* Similar reliability to the Macintosh drive, easily better than the gawdawful Twiggy.)
 

krebizfan

Veteran Member
Joined
May 23, 2009
Messages
5,528
Location
Connecticut
I thought the 8050 required a processor and a good amount of RAM in the drive; rather the opposite of Apple's minimal drive design.
 

per

Veteran Member
Joined
Jan 21, 2008
Messages
3,006
Location
Western Norway
I know for certain that the Olivetti M24 did at least use 80-track double-sided double-density drives, and could come with them in a stock configuration. Maybe the American edition, the AT&T PC 6300, used it too.
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
5,308
Location
Upper Triassic
I thought the 8050 required a processor and a good amount of RAM in the drive; rather the opposite of Apple's minimal drive design.

The 8050 requires a processor and RAM because it's a stand-alone computer that runs the DOS and everything, essentially communicating with the host computer via a network protocol, not because the hardware that writes bits to the disk mechanisms themselves is a whole lot more sophisticated than what an Apple II does. To really cut to the chase the main requirement for doing ZBR is a shift register/UART that can be set to a different clock rate depending on what track you stepped the drive to. That's... not a lot, really. It's certainly not a lot harder to do than what Apple did with the Twiggy and Macintosh drives, which required a PWM generator plus a tachometer/feedback mechanism to vary the drive motor speed. (Which comes with a bunch of mickey-mouse consequences you don't have with the variable data rate solution, like having to give time for the drive motor to settle at a new speed after you've stepped into a different speed zone.)
 

Eudimorphodon

Veteran Member
Joined
May 9, 2011
Messages
5,308
Location
Upper Triassic
I have an 8050 Drive as well. Dont they require 100 TPI or 96 TPI Quad Density Disks (Ideally)?

"Quad Density" disks had the same magnetic properties as "normal" floppy disks, they were just (supposedly) manufactured to a higher quality standard because the narrower heads on the QD drives made them a little more prone to errors due to imperfections in the disk surface. Whether there was ever really any difference in practice is certainly a valid question.

Likewise this does bring up a reliability concern that cropped up with at least the earliest 96/100 TPI drives, which is the narrower tracks also made them more sensitive to alignment errors. Supposedly this was a legit concern when they were first introduced, but certainly by the time they were turning out half-height drives with more reliable positioning systems this was probably a non-issue.
 

VERAULT

Veteran Member
Joined
Jan 30, 2012
Messages
6,207
Location
Connecticut, USA
I know for certain that the Olivetti M24 did at least use 80-track double-sided double-density drives, and could come with them in a stock configuration. Maybe the American edition, the AT&T PC 6300, used it too.
Id let you know but my at&t 6300 has psu issues
 

Chuck(G)

25k Member
Joined
Jan 11, 2007
Messages
40,218
Location
Pacific Northwest, USA
"Quad Density" disks had the same magnetic properties as "normal" floppy disks, they were just (supposedly) manufactured to a higher quality standard because the narrower heads on the QD drives made them a little more prone to errors due to imperfections in the disk surface. Whether there was ever really any difference in practice is certainly a valid question.
I have floppies labeled with "96 tpi" and "100 tpi" manufacturer's labels. This always got the better of me, so I asked a customer engineer at Verbatim (when they were still operating out of Santa Clara). His response? Identical media--if preformatted, formatted at the stated track density, but otherwise, nada. Mostly a sales gimmick.

He did send me some neat samples of the Drivetec/Kodak preformatted stuff, however.
 

nullvalue

Veteran Member
Joined
Oct 8, 2019
Messages
555
Location
Indiana
Just curious if anyone actually used these and in what. I can’t say I ever saw commercial software on this format.

The Tandy 2000 was one of the few computers that came from the factory with DSQD (80-track/720kb) drives that I know of. Pretty cool machine. Also one of the few machines to feature the 80186 CPU.
 

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,056
Location
Minnesota
You're correct as usual, Chuck. I just purchased a Teac FD-55FV-52U since I have several uses for 720K 5.25" in my S-100 equipment. All jumpers were set to defaults as shipped according to the manual except I set DS1 for PC twisty cable.
I put it in a 486 PC set to 5.25" 360K and could format ok but got error trying to format it set to 720K 3.5". But when I put tape over pin 34 I can now format it 720K just fine.

Larry G
 

JohnElliott

Veteran Member
Joined
Sep 1, 2006
Messages
588
Location
Sussex, UK
I had (maybe still have) a 720k 5.25" drive that used to be in a BBC micro external drive case. It had a 40/80 track switch wired to a couple of pads on the PCB. I had it in a 5150 for a while but don't think I got it working.
 

retrogear

Veteran Member
Joined
Jan 29, 2014
Messages
1,056
Location
Minnesota
I also have 4 of the Mitsubishi M4853 96 TPI 720K 5.25". Two go with my CompuPro DISK1A card and two are in my rare Sperry UTS-30 CPM Z80.
 

Patrick.B (TTR)

Experienced Member
Joined
May 11, 2011
Messages
395
Location
Houston, Texas, USA
Tandy 2000 came with 2x Mitsubishi M4852 (720K) drives. used standard DSDD drives, on 80 Tracks.
I have used and still use 5.25" 720K drives on my TRS-80 Model 4's.
 

rpiguy2

Experienced Member
Joined
Dec 15, 2016
Messages
308
Location
New Jersey
All I could find on this subject is below


But I am curious what were 5 1/4” 720k DSQD disk drives used in and what years ?

We’re these just a Commodore thing?

When I was very young one of my friends had a 5 1/4” 720kb internal disk drive which was apparently worth mentioning in the 80’s though I remember nothing else about the machine

I do vaguely remember 720kb 5 1/4” disks at a local computer store but never thought much about it.

Was this a thing you bought if you had an old floppy controller that only supported 720kb to max out your 5150?

Just curious if anyone actually used these and in what. I can’t say I ever saw commercial software on this format.

Thanks
Commodore did produce several Quad Density drives (what you are describing) and they held 1MB. SFD-1001 is one example, and I believe the 8250 is another.


They were not terribly wide spread because they only worked out of the box with the PET and CBM line of machines. To use them with the popular C64 required an IEE488 adaptor - and these drives were much more expensive than the 1541 so they probably wouldn't have sold well.

It isn't easy finding replacement drive mechanisms either these days.
 
Top