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

rmay635703

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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
 

krebizfan

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Not so much Commodore as many S100 and enhanced XT systems. 80 tracks did provide the largest capacity with a double density controller and the drive could read the earlier 40 track disks. Note there were also single sided 80 track double density disks which were most common in a number of DEC system with DEC RX-50 being an oddball design with two drives sharing one motor and one drive mounted upside down. Half the sides; half the capacity. IBM's introduction of the 1.2 MB drive with the controller capable of 300 kbps to read 360 K floppies rather killed off the 720K drives since an AT could not read the 720K diskette without special software.

They were most often seen from 82 to 85 though they were still available later. Disk Trends lists production of 5.25" drives as about 16 million in 1988 with 268,100 being 1 MB (720 K formatted) quad density models.
 

Chuck(G)

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Not at all uncommon in the early 80s. Some versions of the Sanyo MBC500 series had them as an option. The AVL Eagle computers used them. Heck, we used them on the Durango Poppy.

The interesting thing is that electrically, they're the same as the 3.5" DSDD (720K) drives. Many systems chose to format them to 800KB.

Not nearly as unusual as the 100 tpi 77-track 5.25" floppy drives.
 

GeoffB17

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Yes, it's odd that things went that way. The 360k drives ruled for quite a while, and then things seems to move to the 730k 3.5" drives, so it's not that the 5.25/730k format was bypassed , rather sidestepped? Then things went to the HD drives, which happened to be 1.2Mb and 1.44Mb respectively.

Some time after they became common, I got a util called FORMAT42, this provided a system to reuse 360k floppies in a HD drive as 730k format, in effect the same format as was used on the DSDD 3.5" disks - this making sense given that people might have lots of DSDD 5.25" disks laid about not a lot of use. I used this software quite a lot, I certainly had lots of the disks. There was the prog to to the format, and 99% of my disks formatted quite happily. And still work today. There was also a little .SYS file that tweaked the DOS system to a) allow the special format to be recognised by DOS properly, and b) to allow the HD drive to be quickly swapped between HD and the 80t/DD format. It wasn't really referred to as QD, but maybe it was?

The notes/doc for the system suggested that it might not work on all systems/drives. But it worked fine for me. It was also possible to try for 81 or 82 tracks, or I think 10 sectors per track, but I was quite happy with the 730k format.

The system is still active on one of my old PCs.

Geoff
 

Chuck(G)

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the 1.2 MB drive with the controller capable of 300 kbps to read 360 K floppies rather killed off the 720K drives since an AT could not read the 720K diskette without special software.
For the AT, all it took to read the things was to reset the "double-step" bit in BIOS RAM. You could add a 720K 5.25" drive to a PC and call it a 3.5" one as well. Or you can use a device driver.
 

Chuck(G)

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Been there, done that.

DOS720 Version 1.02

Distribution Information

April, 1995

---

DOS720 is a device driver to allow PC XT- and AT-compatibles to read and write
DOS 720K MS-DOS diskettes (720K, 80 track, double-sided).

To install, copy the DOS720.SYS file to the root directory of your C:
drive and insert the following statement into the CONFIG.SYS file:

DEVICE=DOS720.SYS

DOS720 will automatically locate the first 5.25" 1.2MB drive and assign a
new drive letter to it for 720K access.

The drive may also be explicitly specified with the /D argument. So

DEVICE=DOS720.SYS /D:1

specifies that the second diskette drive (usually B: ) should be used.

DOS720 will also work with secondary diskette controllers provided that
they are configured to use DMA 2 and IRQ 6. In that case, the /P argument
may be used to specify the I/O port address of the diskette controller. The
/D argument must also be used in this case. For example:

DEVICE=DOS720.SYS /D:0 /P:370

specifies that the first diskette drive on the diskette controller located at
I/O port 370 (hex) will be used.
 

bolex

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I never could get any of my older DOS machines to work with a 720K 5.25" drive via the BIOS by tricking it to thinking it was a 720K 3.5". However, I did get the SUNIX floppy driver to work. In the config.sys, I said it was a 720K 3.5" floppy and it worked just fine. I was just curios and playing around. I'm not sure how cross-compatible that would ever be.
 

bolex

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What was the error when you tried? Note that it must be a genuine 720KB 5.25" drive. For example, a Teac FD55F (not GF).
The 720K floppy I have is a TEAC FD-55FV-03-U. I would not get an error until I tried to format the disk. I can't recall the specific error. I'll have to throw it back into the machine to verify.
 

SomeGuy

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On a quad density drive, you may have to change the jumper, if it has one, for pin 34 READY/DSKCHG for a BIOS to recognize it as a 3.5" 720k. Otherwise it will only work with the 360k setting (it will look like a 360k drive but extra tracks can be formatted with a third party formatter).

The important thing is that IBM never supported quad density drives. Also, 5.25 disks written as 360k in a quad density drive will not be reliably readable in a genuine 360k drive. PC clones with quad density drives were considered "not IBM PC compatible" (even if everything else in the system was compatible).... and then IBM created exactly the same problem with the IBM AT and 1.2mb drives.
 

1ST1

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Some of the Olivetti M21 and M24 had 5,25 inch floppy drives from Toshiba by factory. Specially those without harddisk. Initially they have been defined as 640 kB drives, but later then 720. The difference is only the disc format, 8 versus 9 sectors per track.
 

bolex

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720K floppy I have is a TEAC FD-55FV-03-U.
So I pulled this drive out to take a look at it to try to figure out why it didn't work for me before. This drive does not have a DC jumper - just an RY (Ready), so it would not work in the AT I was using. However, I just now connected this to my Compaticard IV and set it up to be that strange 800K format that they have. To get that to work I just configured the setting in config.sys to indicate that the drive has no disk change. It worked fine there.
 

Chuck(G)

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That 800K isn't all that strange--it just squeezes 10 sectors on a track. Even some CP/M systems do this, like the Columbia 1600 running CP/M-86.

Try putting a piece of tape over pin 34 on your drive and call it a 3.5" 720K on your AT system. It'll probably work.
 

tezza

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Yes, I had one of these drives. 80 track, double sided, 5 1/2 inch. I used it on my Dick Smith System 80. My disk controller was single density so all up 400k. Year was around 1984 or so.

Tez
 

VERAULT

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It makes sense to me. Twice the capacity of 360KB low density. In Fact its strange that it jumped to 1.2MB without an inbetween capacity like 720KB.
If you ask me 720KB 3.5" makes less sense. It started out as 400KB on the first single head sony drives (used by Apple) then doubled to 800KB with the addition of a second R/W head. Why the Pc market used 720 was strange.. and kept that format to the 1.44MB
 

krebizfan

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Apple had that weird GCR with variable rotation rates format. Had Apple implemented MFM and kept the variable rotation adding more sectors to the outer tracks, the disk would have been able to store about a megabyte.

A 3.5" drive at 300 RPM with the same double density data rate yields the same capacity as the 300 RPM 5.25" drives per track. I wish IBM had waited about 6 months for TEAC to come out with its 300 RPM 5.25" high density drive which would have had a capacity of 1.44 MB. That would have made floppy drivers easier since there wouldn't be a weird 300 kbps mode. Using 1.2 MB drives gave IBM a brief advantage until new controllers became widely available. Other companies would have needed either more expensive drives with dual speed motors or the addition of a double density drive to read the standard 360K disk.

There were a few formats that used the 300 kbps mode on 3.5" drives to push the double density storage capacity over a MB but those disks can only be read with a high density controller.
 
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Chuck(G)

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Apple format is a type of GCR, not MFM. But of course, you know that.
MFM has been a standard modulation since long before the Apple or PC. But of course, Apple had to do its own thing--before it eventually went to MFM.
In fact, it's pretty easy to format a 3.5" 250Kb/sec drive to 800K (10 sectors of 512 bytes). Some older CP/M systems used 5 sectors of 1024 bytes as well.
NEC never fell for the low-density stuff on its PC98 boxes. 8" was the same as 5.25", which was the same as 3.5". 360 RPM, 500Kb/sec data rate.
 

Chuck(G)

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Apple had that weird GCR with variable rotation rates format. Had Apple implemented MFM and kept the variable rotation adding more sectors to the outer tracks, the disk would have been able to store about a megabyte.
And be the same as that well-known and universally-adopted format that the Sirius Victor used? No thanks.
 

krebizfan

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And be the same as that well-known and universally-adopted format that the Sirius Victor used? No thanks.

Sirius might have benefitted from a degree of data sharing. The Apple 400K and 800K drives could not read any non-Apple format anyway so what is the difference between having the unique Apple 3.5" formats being GCR or MFM. Apple had to switch to new integrated controller chip design for the 3.5" drives so there wasn't even much of a backwards compatibility issue.
 
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