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Wanted : 720kB 3.5" Floppy Drive

1

1200XL M.U.L.E.

Experienced Member
Joined
May 9, 2021
Messages
84
Now that I have a 360kB floppy drive :) :) I am looking for a 3.5" 720kB floppy drive.

Does anyone have a unit in good working condition they can offer me?

I am located in the US.

Thanks!
 
Note that most internal 1.44 MB drives will work as 720K drives when attached to a double density controller. Just something to consider if the offered 720K drives are expensive or seem badly worn.
 
krebizfan said:
Note that most internal 1.44 MB drives will work as 720K drives when attached to a double density controller. Just something to consider if the offered 720K drives are expensive or seem badly worn.
Click to expand...

Hi krebizfan !

That kind of blew me away. So you're saying I can broaden my search to include 1.44MB and there's a good chance it will work as a reliable 720kB drive? That's awesome! :) I noticed you said "most internal 1.44 MB drives will work as 720K drive" which means some won't. Is there any one drive I should seek out or avoid?

Chuck(G) said:
Also, check the Amiga community. One of the more commonly-used drives is the Teac FD235F--a respectable 720K DD drive
Click to expand...

Hi Chuck(G) !

Thanks for the tip! A quick search on Google and eBay shows the drive with suffixes of HF and HG ... but not simply F. The H seems to signify high density. Would it still work in DSDD application like suggested by krebizfan ?
 
Sure it will, but it will be sensitive to the density indication hole on an HD floppy. So if all you have are HD floppies and want to write a 720K format, cover that hole over with a bit of (opaque) tape. The 235F obviously has no such sensor. One consideration to observe is that if you're using the drive on a non-PC system (say, an old Amstrad Joyce), pin 34 being DRIVE READY may be required. Most 235HF drives have that pin assigned as DISK CHANGED.
 
1200XL M.U.L.E. said:
Hi krebizfan !

That kind of blew me away. So you're saying I can broaden my search to include 1.44MB and there's a good chance it will work as a reliable 720kB drive? That's awesome! :) I noticed you said "most internal 1.44 MB drives will work as 720K drive" which means some won't. Is there any one drive I should seek out or avoid?
Click to expand...

That is correct. I have had good success with the Teac FD-235 line mentioned by Chuck(G). The FD-235F is the 720K model; the FD-235HF is the 1.44/720K model. I think those were actually the same drive mechanism just with different jumper settings.

PS/2 floppy drives probably will not work. Some of the last 1.44 MB drives manufactured didn't have support for 720K disks, doing the same cost reduction efforts as happened for USB floppy drives.

http://minuszerodegrees.net/5160/flo...ve_support.htm explains how it works with the IBM XT. The Equity 1+ should be similar except that the Epson should also format.
 
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1200XL M.U.L.E. said:
I noticed you said "most internal 1.44 MB drives will work as 720K drive" which means some won't. Is there any one drive I should seek out or avoid?
Click to expand...
A few of the last 3.5" drives produced cut corners, saving perhaps 3 cents per drive by dropping 720k support. Also drives from non-IBM PC style systems or laptops may not work in a desktop PC. For example 3.5" drives from a Macintosh can not work in a PC, they don't even have the same connector.

When in doubt, get the model number and look up technical information. You usually want to look up jumper information anyway just in case someone has messed with the jumpers.
 
FWIW I'm currently using a 1.44 3.5 floppy on my 1000SX and it see it as a 720 without any software support, just "plug 'n play". Also, some earlier 3.5 floppy drives may have a jumper on the PCB which will let you select 1.44/720.
 
I have a couple of those drives and 5.25" adapters. It doesn't change drive operation--the drive is still sensitive to the "media sense" hole. The 720K/1.44M mod that the document talks about has nothing to do with media density, but rather whether pin 34 is READY or DISK CHANGED. Try it yourself. I can include a photo of the adapter PCB if desired.

Here's another one which, at first blush, would seem to do what you're asking, the Samsung SFD-321B. The document says that it honors pin 2 "density select", but that's only partially true. That pin, if jumpered, only selects between 1.6M and 2.0M operation if high-density media is inserted (1.6M = 360 RPM high density; 2.0M = 300 RPM high density). You can't force 720K mode with a high-density floppy inserted. FWIW, the SFD-321B is my "go to" drive when I get requests for oddly-configured drives, such as some of those used in Mitsubishi PLCs where pin 34 is "ready" and pin 2 is "disk changed" and high-density operation is 1.6M.
 
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Chuck(G) said:
I have a couple of those drives and 5.25" adapters. It doesn't change drive operation--the drive is still sensitive to the "media sense" hole. The 720K/1.44M mod that the document talks about has nothing to do with media density, but rather whether pin 34 is READY or DISK CHANGED. Try it yourself. I can include a photo of the adapter PCB if desired.

Here's another one which, at first blush, would seem to do what you're asking, the Samsung SFD-321B. The document says that it honors pin 2 "density select", but that's only partially true. That pin, if jumpered, only selects between 1.6M and 2.0M operation if high-density media is inserted (1.6M = 360 RPM high density; 2.0M = 300 RPM high density). You can't force 720K mode with a high-density floppy inserted. FWIW, the SFD-321B is my "go to" drive when I get requests for oddly-configured drives, such as some of those used in Mitsubishi PLCs where pin 34 is "ready" and pin 2 is "disk changed" and high-density operation is 1.6M.
Click to expand...

That's all good to know, but at least the 1000SX doesn't care and will treat any 1.44 as 720 without and mods. I'm assuming it would work on other PC's of that ilk about the same.
 
Agent Orange said:
That's all good to know, but at least the 1000SX doesn't care and will treat any 1.44 as 720 without and mods. I'm assuming it would work on other PC's of that ilk about the same.
Click to expand...

You're missing the point, I think. Stick an HD floppy in a 1.44M drive installed in a 1000SX and see how well that works--try to format and write it as 720K without blocking the media-sense hole.
 
Chuck(G) said:
You're missing the point, I think. Stick an HD floppy in a 1.44M drive installed in a 1000SX and see how well that works--try to format and write it as 720K without blocking the media-sense hole.
Click to expand...

I'm willing to concede that point, but I bought a large quantity of those 720's from you a few years back, so no need to block anything. :rolleyes:
 
Chuck(G) said:
You're missing the point, I think. Stick an HD floppy in a 1.44M drive installed in a 1000SX and see how well that works--try to format and write it as 720K without blocking the media-sense hole.
Click to expand...

But that is a good thing, avoiding all the issues of wrong formats. I seem to remember that some of the 720K drives sold in the early 90s had media sense detectors and would only work with disks lacking the hole. Thirty year old memories can be be unreliable.
 
Again, can you cite an example? I can't. All the 3.5" DD drives that I have don't have the media sensor.

I occasionally get batches of 3.5" WP disks that are formatted in DD but are HD media. As I mentioned, there are cases where HD media recorded as DD actually outperform the older DD disks.
 
Chuck(G) said:
Again, can you cite an example? I can't. All the 3.5" DD drives that I have don't have the media sensor.

I occasionally get batches of 3.5" WP disks that are formatted in DD but are HD media. As I mentioned, there are cases where HD media recorded as DD actually outperform the older DD disks.
Click to expand...

Chuck, I never mentioned anything about a 'media sensor' I was referring to a simple soldered-in wire like jumper on the drive's PCB that could be configured for either as a 720 or 1.44 drive. What kind of an example can I offer up for that? They exist but not on recent 3.5 drives I have found.
 
I was responding to this post:


krebizfan said:
But that is a good thing, avoiding all the issues of wrong formats. I seem to remember that some of the 720K drives sold in the early 90s had media sense detectors and would only work with disks lacking the hole. Thirty year old memories can be be unreliable.
Click to expand...

I've never seen a native 720K 3.5" drive with a media-type sensor. I have a strong suspicion that they never existed.
 
Chuck(G) said:
I was responding to this post:




I've never seen a native 720K 3.5" drive with a media-type sensor. I have a strong suspicion that they never existed.
Click to expand...

I remember someone having this issue with a replacement 720K floppy about 1993. I failed to take notes.
 
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