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How can you tell 8" disks apart

K

kb2syd

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I have a bunch of unlabled 8" soft sector disks. Hundreds of them in fact. I know that you can tell if they are SS vs. DS by the placement of the index hole. I think 12 o'clock is DS and 2 o'clock is SS.

Is there any difference between SD and DD disks? How about the media. I've read that there is no physical difference, but I have an image of an 8" disk that won't write correctly, but I can read without a problem. Yes, I have the write enable tab in place.
 
I have a bunch of unlabled 8" soft sector disks. Hundreds of them in fact. I know that you can tell if they are SS vs. DS by the placement of the index hole. I think 12 o'clock is DS and 2 o'clock is SS.
Click to expand...

SS is about 12:30 and DS is about 1:00

Is there any difference between SD and DD disks? How about the media. I've read that there is no physical difference
Click to expand...

Lots of good info at http://retrotechnology.com/herbs_stuff/drive.html

Looking at the '8 inch' specs, I think that after the DD format diskettes were introduced, the manufacturer probably graded the disks like:
1. Manufacturer tests selected tracks on a diskette/s from each batch of diskettes.
2. If tracks can be formatted reliably at 500 Kbps (MFM), the batch becomes DD.
3. Those batches that fail at 500 Kbps are tested at 250 Kbps. Those that pass become SD. Those that fail are discarded.

Depending on demand, some batches of DD may be labled as SD.

With that in mind (assuming that it's true), substituting a SD for a DD is not recommended.

but I have an image of an 8" disk that won't write correctly, but I can read without a problem. Yes, I have the write enable tab in place.
Click to expand...

Perhaps your drive has a write problem. Or is it a case of some images being written okay, but not one particular image?
 
I found the problem with the help of Dave Dunfield, and I've discovered 2 things in the process:
1) There is apparently no difference between SD and DD media in the 8" world. I don't know if this has always been true, but it seems true for "newer" 8" media.
2) Just because your floppy controller can READ a disk doesn't mean it can write it. This particular media was SD on Track 0 and DD for the remaining 76. Track 0 was 26 sectors at 128 bytes each. Tracks 1-76 were 16 sectors at 512 bytes each. So, even though the controller supported FM on track 0, it couldn't handle 16x512 for the rest of the disk.

I left the onboard floppy controller and installed an Adaptec 1542CF with the floppy set to secondary. Worked great. ImageDisk and its associated utilities are trerrific tools. If you need to archive or copy FM and/or MFM diskettes, try this software.
 
I thought that double sided vs. single sided was a matter of 'surface finishing' on the side designed to be written. ie: The side designed for data would be highly polished and tested, whereas the unused side might not be as properly finished and definitely not tested. It is also possible that the unused side might have a defect that introduces a transient error.

The second issue is the liner. If a dolt designed the jacket, flipping the disk over and using the untested side might release particles that were trapped in the liner because the disk will be spinning opposite of it's intended directly.
 
Yes, I was just about to suggest the ol' SD Track 0, DD disk problem, but I see you've already found it. You'll run across that a lot in dealing with CP/M disks.

The 8" DS disks are different from the SS, to discourage folks from using them interchangeably, perhaps for the reasons Mike points out. Double-Sided 8" drives actually have the optical sensor thinggy in both index-hole locations, so they can use either type of disk.

--T
 
I wasn't referring to the index hole - I was referring to the spinning media itself.

A true single sided disk, besides having the index hole in a different place, might also have the unused side 'less prepared' and untested vs. the correct side. Depending on the preparation required, it might even look like a slightly different shade of rust than the correct side.
 
Also, since the side index hole is not aligned to the axis, you'd have to punch new holes in the jacket (and not the media) or add a new index sensor if you wanted to do anything meaningful when flipping over the disk.

All the disks I've looked at in the past few days appear to have the same color and finish on both sides regardless of location of the side index sensor.
 
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