Disk density question

[RobertLM78]

Greetings 99ers! So, I'm wondering if any disk density can be formatted as single density, particularly HD disks? I've never actually had a problem formatting DD disks as SD, but I sure seem to be having a problem with these HD disks I came into. Thanks for reading!

[RXB]

If using a SCSI card the ONLY way to format is with the SCSI formatter. It came with the SCSI card.

I would have to pull out a copy of all the SCSI stuff I have in my storage. Maybe someone else has it.

 

I do not know what Hard Drive card you have.

[+OLD CS1]

The short is, yes, but not reliably. The longer answer is high density disks have a higher coercity and the older lower-density heads have problems setting the magnetic domain. If you do use high density disks, you want to absolutely ensure there's nothing already written on the disk otherwise you have the problem of half-track writing and magnetic bleed-through. Even then there is no guarantee of operation.

 

This is discussed ad naseum in other retro forums and there are a few good articles on the Intarwebs discussing the issue with more in-depth and technical information. Interesting reading.

[marc.hull]

Greetings 99ers! So, I'm wondering if any disk density can be formatted as single density, particularly HD disks? I've never actually had a problem formatting DD disks as SD, but I sure seem to be having a problem with these HD disks I came into. Thanks for reading!

 

You can tape over the HD detect hole. That will work for a while but is pretty risky on several fronts. The HD media is chancy as far as long term storage.

 

If you ever take the tape off the drive and try to READ/WRITE to it then you will destroy the contents. I did say -->READ<----

 

--> READING<-- a HD disk on the TI without the HD detect defeated (Tape ET AL) will ruin the contents of the disk

 

 

Go to Ebay and buy DD disks and forget all your troubles. Sorry so serious but it is a real PITA when you (or I) make this mistake and ruin our data.

[RobertLM78]

Thank you all for the informative responses. So where is the HD detect hole? I will give that shot - I'm not putting anything irreplaceable on these disks anyway . I can also try and stick just a one or two files on it, as that doesn't seem to be a problem. It's when there's bunch of files, as CS1 was alluding to, that things get dicey. Or, I guess I can try to see who here can make use of them and do a trade .

 

Edit: Let this be a lesson to all to look closely at the description before buying your disks

Edited July 7, 2013 by RobertLM78

[marc.hull]

Thank you all for the informative responses. So where is the HD detect hole? I will give that shot - I'm not putting anything irreplaceable on these disks anyway . I can also try and stick just a one or two files on it, as that doesn't seem to be a problem. It's when there's bunch of files, as CS1 was alluding to, that things get dicey. Or, I guess I can try to see who here can make use of them and do a trade .

 

Edit: Let this be a lesson to all to look closely at the description before buying your disks

 

What CS1 was alluding to was making sure it was a virgin disk. 1.44's previously written too by a PC are a mine field. The HD hole is opposite the write protect hole (the one with the sliding tab and the "lock" icon.

[RobertLM78]

Ah, for a 3.5" disk I presume? Therein lies the confusion - these disks are 5.25" HDs, so they don't have any HD detect hole . Sorry about that - I should have been more clear as to what form factor the disks were, although I'm sure a lot of the caveats still apply.

 

Well, can anyone here make use of these 5.25" HD disks (10)? They're yours if you can - just reimburse the shipping, or trade me for some DD 5.25" disks .

Edited July 7, 2013 by RobertLM78

[marc.hull]

Ah, for a 3.5" disk I presume? Therein lies the confusion - these disks are 5.25" HDs, so they don't have any HD detect hole . Sorry about that - I should have been more clear as to what form factor the disks were, although I'm sure a lot of the caveats still apply.

 

Well, can anyone here make use of these 5.25" HD disks (10)? They're yours if you can - just reimburse the shipping, or trade me for some DD 5.25" disks .

 

Slaps head....... 1.2's huh.....Nevermind .....

[RobertLM78]

Slaps head.......

You and me both

[+FarmerPotato]

Necropost. I needed answers to the question of 5.25 HD floppies in DD drives.

As @OLD CS1 said, it comes down to coercivity of the coating.

I found lots of detail on Retrotechnology.com , particularly a long interview with Chuck Guzis 

 

Elsewhere, media details, by the numbers:

5.25" double density, 40-track 360K floppy media

Mylar, 0.003 in thick (.0008mm)
iron oxide coating, 300 oersteds coercivity
same for 80-track
drives: 300 RPM

5.25" high density, 80-track 1.2MB floppy media
cobalt coating, 600 oersteds coercivity
drives: 360 RPM

 

 

 

Other takeaways from the interviews:

3.5" floppy DD 
660 Oersteds (Oe)
1.9 microns

3.5" floppy HD 
720 Oersteds (Oe)
0.9 microns

In 3.5", the coercivity is not the problem. The lesser amount of magnetic domains (particles) in the HD floppy, gives a weaker signal back to a DD drive. Also, the DD drive writes with higher current and lower rotation speed, increasing the problem. 

Anecdotally, you may get away with 3.5" DD disks that are unformatted or thoroughly degaussed.
But the higher write current makes the disk more difficult to erase or re-write, so it is not reliable (except as read-only?)