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

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...
 
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.
 
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.)
 
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.
 
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.
 
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.)
 
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.
 
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
 
"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.
 
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.
 
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
 
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.
 
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.
 
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.
 
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.
 
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