• Please review our updated Terms and Rules here

DSDD vs DSHD vs DSQD

L

Lorne

Veteran Member
Joined
Jul 26, 2008
Messages
1,164
Location
Chandler, AZ, USA
I've seen (DSDD) double sided double density 5 1/4" disks, and (DSHD) double sided high density 5 1/4" disks.
What is the difference?
Is DSHD equivalent to (DSQD) double sided quad density?

I'm trying to find some DSQD but I've never seen them, noted as such, on Ebay.


Thanks,

Lorne.
 
Not sure.

DSDD are 360K, DSHD are 1.2MB.

3.5" disks did end up ar 2.88MB (DSQD?) the 5.25" was dead by then.

I have a new box of Imation disks that are odd. The disk sleeves state DS, DD 500K and do not have the center hub ring like every other 360K floppy I have ever seen (they look like a normal 1.2MB floppy.
 
I just checked with Athena.
Their model number 47-8801 is a QD disk (although their website lists it as DD). $ 35/box of 10 disks is a little steep (minimum 2 box order).
This retro stuff isn't cheap!
 
Lorne said:
I just checked with Athena.
Their model number 47-8801 is a QD disk (although their website lists it as DD). $ 35/box of 10 disks is a little steep (minimum 2 box order).
This retro stuff isn't cheap!
Click to expand...

Yeah, $70 for a 20 floppy's is a bit hard to fit into a tight budget for certain. I think I'll stick with the DD's right now and see how things go. Thanks for the information though. I was wondering why they didn't have and QD's listed.
 
The only difference between QD and DD 5.25" diskettes is the verification performed as part of the production process. This came from a very reliable source at Dysan. In most cases, you can do the selection from DD media yourself and save a pile of money.

There was a time when single-sided-labeled media was available also. These were primarily the result of selecting the "good" side from the cookie used for DS media.

Here's one for the specialists. What was the media formulation used for the Drivetec 6.4 MB 5.25" diskettes? I suspect it was the same as HD media, but that's only a guess.
 
In any case, all "QD" floppy disks I've seen have been labeled DSDD 96 tpi, nothing else. To add to what Chuck writes, I've heard that some manufacturers producing 96 tpi quality disks sold them as 48 tpi once the QD drive systems had gone extinct, to not confuse buyers.
 
I got hold of a new box of DSQD disks. They're Athana disks, and the label even says "double sided / quad density / soft sectored / 96 TPI".

Now here's the weird bit:
I put these in my Altos 5/15 (with the A drive on the right and the B drive on the left !) that is supposed to be using DSQD drives, and I can format them, but then can't copy to them.
When I use a 3M DSDD soft sectored 48 TPI disk, I can format them, and copy to them with no problems.

I did an MP/M diskstat on the Altos and I got the following info back:
Floppy & drive B: 80 cyls, 2 heads, 9 sectors per track
Two heads tells me it's a DS drive. Does the rest of the info tell me I've got DD or QD, or do I need more info?

What gives?

Edited for additional info:

I just checked the manual that was very recently posted at Bitsavers.org.

From the manual:

Drives: Control Data 9409T 5 1/4"

Performance Specifications:

Capacity - unformatted double density
Per disk: 1 megabyte
per track: 6.25 kilobytes

Altos format (CP/m, MP/M)
Per disk: 737 kilobytes
# of cylinders: 80
# of heads/cyl: 2
# of sectors per track: 9
Sector size: 512 bytes
Block size: 4 kilobytes
# of files: 180

Functional Specifiations:

Disk diameter: 5 1/4"
Rotational speed: 300 rpm
Track density: 96 tpi
Total tracks: 160 (80 per side)
Encoding method: MFM
Index holes: 1

So is it double density or quad density, and if it's quad, why can't I write to the DSQD disks?
 
Last edited by a moderator:
Terry Yager said:
It's (nominally) QD all right, but I'll tell ya, I've always had better luck using DD media in a QD drive too...

--T
Click to expand...

You are right.
I had no problem using the DSDD disks.
The one DSQD I was using turned out to be a bad disk - I kept getting BDOS errors. I tried another, and while it took alot longer it worked.

Look at this crap:
View attachment 864
It's tough to see but the disk on the left is one of the DSQD disks by Athana. Notice the sticker indicating quad density & 96 TPI. Now look at the one on the right - I peeled the sticker off (taped onto the right side), and what's underneath but the same model number with a double density & 96 TPI designation. Those bastards !

That's exactly what Carlsson said in a previous reply - DSDD with 96 TPI.
 
Last edited:
I routinely use DSDD disks in place of the DSQD disks. I never have problems. This includes the Altos 5-5AD (similar to yours) and the Commodore 8050/8250/sfd-1001, etc.
Bill
 
Smae here - and for the last 15 years on the Tandy CoCo3. I have used for years, the Mitsubishi M4853 DS/QD drives on the CoCo, and DS/DD media.

DS/DD and DS/QD media is basically the same. AS others have mentioned, they might have done testing at 96tpi DS/QD to certify it, but the media and coating is the same.
Only difference, is that the the DS/DD is 48 tracks-per-inch using 40 tracks, and DS/QD is 96 tracks-per-inch using 80 tracks. Basically, the DS/QD drive put 80 tracks, or cylinders, in the same space that a DS/DD 48tpi drive puts 40. Density is the same: 512 bytes-per sector, 9 sectors per track IBM standard (others may differ a little, obviously) but it is still double-density. a high-density 5.25" is 15 sectors-per-track, and uses different media on the actual disk, and a high-density 3.5" 1.44MB disk is 18 sectors-per-track, and again, uses different magnetic coating than what is on a 3.5" DS/DD 720KB diskette.

Long story short: DS/DD and DS/QD 5.25" media are virtually the same, and I have DS/DD disks that have been in use as DS/QD for over 15 years, and are still readable.

T
 
Lorne said:
You are right.
I had no problem using the DSDD disks.
The one DSQD I was using turned out to be a bad disk - I kept getting BDOS errors. I tried another, and while it took alot longer it worked.

Look at this crap:
View attachment 864
It's tough to see but the disk on the left is one of the DSQD disks by Athana. Notice the sticker indicating quad density & 96 TPI. Now look at the one on the right - I peeled the sticker off (taped onto the right side), and what's underneath but the same model number with a double density & 96 TPI designation. Those bastards !

That's exactly what Carlsson said in a previous reply - DSDD with 96 TPI.
Click to expand...
--------
Sigh - here we go again...

As discussed in several other threads, Quad Density is an ambiguous term for Double Density disks used at either 96 or 100 tracks per inch instead of the usual 48 (or 35 on some really old stuff). So, why are Athana bastards? QD disks *ARE* DD disks 'certified' for use at 96TPI, although the manufacturing techniques and QC of 5 1/4 disks soon improved and normal DD disks are now as good as or better than the old 'certified' QD disks. Of course Athana's disk may well be ordinary DD disks with a QD label for those who insist; nothing wrong with that, especially if they're actually certified - you pay for the label.

The circumferential density is the same; at 512 bytes/sector and 9 sectors per track on a 40 track DSDD disk you get 512 x 9 x 40 x 2 = 368640 bytes. A 96TPI "QD" drive puts the tracks closer together and doubles the RADIAL density (double x double = quad) and gives you twice as many tracks (80) and twice the capacity (this format is also usually used on 'low' density 3.5" disks, BTW)

Just to round out the discussion, 5 1/4 HD disks use a different magnetic material which makes it possible to increase the circumferential density (the one that counts) so that they can have 15 sectors of 512 bytes/sector in a track, and 80 tracks (also at 96 tracks per inch) give you 15 x 512 x 80 x 2 = 1,228,800 bytes.

m
 
Ahh, so that explains a lot. The (vintage) QD labeled disks are made with older, less reliable technology, so more recently made DD disks are likely to be better than the older ones...especially after they're 20 years old. I get it (never thought of it that way before).

--T
 
And I still don't understand the difference between 96 tpi and 100 tpi floppy disks, if the systems using those only format 77-80 tracks anyway. To me, the tpi number should indicate the maximum number of tracks possible to format, and as the disks are soft sectored it should work either way.

How big area of the floppy disk surface does a floppy drive generally format, less than one inch? For example if the R/W head can access 0.85" from innermost to outermost position, it should be good enough for 81 tracks on a 96 tpi floppy, or 85 tracks on a disk certified for 100 tpi. Am I making some mistake in my thinking?
 
carlsson said:
And I still don't understand the difference between 96 tpi and 100 tpi floppy disks, if the systems using those only format 77-80 tracks anyway. To me, the tpi number should indicate the maximum number of tracks possible to format, and as the disks are soft sectored it should work either way.
Click to expand...

There's no practical difference in the media, but the 100 tpi drives, in addition to a different track width, place cylinder 0 where the 96 tpi track 6 is located. But that's not enough to render some media suitable for 100 tpi and not for 96 tpi. Most likely, the rating relates to the certification process used during manufacturing.

But this is just noise in the picture. Compared to the various modulation techniques used on floppies (FM, MFM, MMFM, GCR (of various flavors)) and variations in drive electronics and mechanicals, the 100/96 tpi designation is immaterial as regards reliability.
 
You must log in or register to reply here.
Back
Top