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IMD can't read 250kHz disk in 360K drive

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alank2

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I formatted a couple of disks on my Kaypro 4/83 and wanted to read them in using IMD on my PC/AT. The format is 10 sectors * 512 bytes per sector, 40 tracks.

I can read the disks using the 1.2M drive A: on the AT, but not the 360K drive B: on it. My Compaq can also read it with its 1.2M drive. When trying to read it in the 360K drive, it doesn't guess the first track properly and then has errors unlike the other 1.2M drives read it. I have written images to the 360K drive and used them on the Kaypro so I can write images to it, but not read them. Any ideas?
 
A couple of things come to mind. First set the BIOS for Drive A to be 360K. Then start IMD and use "S" for settings.
Set A for 40 tracks, Double Sided, Double Step=ON, and Full analysis.

Try formatting the floppy to see if it formats properly. There is also a "TESTFDC" program included in Dave Dunfield's
Utility software. Run that to see that your Floppy Disk Controller (FDC) passes the proper tests. Plus you can run
the RPM test in IMD ( ver 1.18 ) to make sure it's at 300 RPM.

Larry
 
The A: 1.2M drive does work, it is the B: drive that doesn't read, I tried changing it to B:, 40 tracks, double step off, full analysis on or off.
 
But, Don't you want a 40 track Floppy when finished? For an 80 Track drive you set Doublestep=OFF to get 80 full steps, and for a 40 track
Floppy as a written floppy you set Doublestep=ON to do two steps for every 40 tracks.

It could be the B: drive that doesn't work correctly is a bit out of alignment. Try formatting it as a 40 Track, copy some image to it, then
read that image back in, and do a binary compare of the two files.

Larry
 
I was wanting to be able to both read and write using the 360K drive. It seems to be able to write, but if I wanted to read a disk for others to use, it would seem to be the one to use. I _can_ read a 40 track disk in the 1.2M drive, but at 300kHz and not 250kHz, so would that be a properly archived disk since it was sampled at the wrong speed because of the HD drive? Everything I've written on the 360K/B: drive has been readable with the unaltered alignment 360K drive on the Kaypro and other PC drives I have. I saw a note in imagedisk about it being too fast RPM and that sometimes a bit slower can fix things, like 290 rpm or something, but I'm not sure I want to try that.
 
What precisely does ImageDisk say when it tries to analyze and read the disk?

Ideally I'd dump the problematic disk in the problematic drive with a Kryoflux/SCP, which should reveal what is really going on on the disk surface.

It is possible to write back a 250kbps IMD disk read in at 300kbps using the "translation" setting. But that does get annoying. The included IMDU tool is supposed to be able to alter this setting in an IMD file, but I seem to recall having problems with that the last time I tried it.

In practice, 10 sectors of 512 bytes per track is a little crowded on each track, so speed issues are a little more likely to affect it. I would at least check the drives both on the PC and the Kaypro to see what the RPM rate currently is.

Of course, there could be a number of other odd issues at play here. If you have not already done so, try different disks, and clean all the drive heads.

I think what you are trying to do really SHOULD work as-is.
 
>What precisely does ImageDisk say when it tries to analyze and read the disk?

I'll take a screenshot tonight.

>Ideally I'd dump the problematic disk in the problematic drive with a Kryoflux/SCP, which should reveal what is really going on on the disk surface.

>It is possible to write back a 250kbps IMD disk read in at 300kbps using the "translation" setting. But that does get annoying.
>The included IMDU tool is supposed to be able to alter this setting in an IMD file, but I seem to recall having problems with that the last time I tried it.

Interesting, I can look at that.

>In practice, 10 sectors of 512 bytes per track is a little crowded on each track, so speed issues are a little more likely to affect it.
>I would at least check the drives both on the PC and the Kaypro to see what the RPM rate currently is.

On the Kaypro it is right at 300. I can't recall if I checked the PC.

>Of course, there could be a number of other odd issues at play here. If you have not already done so, try different disks, and clean all the drive heads.

Heads were cleaned a few weeks ago.

>I think what you are trying to do really SHOULD work as-is.

I would think so too; it can write them.
 
Here's the bottom line:

A PC disk controller is blind for a certain period (usually about 500 µsec) after the trailing edge of the index pulse. (Older non-A 8272/765 controllers are blind for 1 millisecond). On standard (IBM System 3) format disks, this is the time that the index address mark (IDAM) passes under the head, so it isn't a problem. However, systems using the Western Digital WD17xx and 27xx FDCs don't demand that the IDAM be included in the format and most vendors left it out, giving a bit more leeway to improve the inter-sector gap spacing.

Since the width of the index pulse varies from drive manufacturer to manufacturer, different drives will give different results. The certain indicator of this issue is that the PC doesn't see the first sector on the track.

In the old days, one of the dodges was to simply block the index mark at the drive interface (a bit of tape over the edge connector pin works). Of course, formatting, which depends on the index pulse, won't work, but reading should work. Before cheap microcontrollers, I used my own lashup on a PC ISA card using a WD1772 FDC.

This almost always is the case with 10-sector x 512 byte formats from WD FDC systems.

I've posted on this in years past. Obviously, collective memory is short.:rolleyes:
 
This is a 5170 with the standard controller. It will read using the 1.2M drive however.
 
Read my post again--drives differ in how they report the index pulse. I'm guessing that you can format, write and read PC-format 360K disks in the 360K drive all day.

As I said, if the symptom is that the first sector of a 10/512 disk can't be read in the 360K drive, you now know why.
 
Maybe I misunderstood, I thought you were saying it was a limitation of the controller, but why then would it work with a 1.2M drive? Wouldn't the same limitation be a problem?
 
I was able to read it in the 1.2M, then use IMDU to translate it to 250kHz, then write it and have it work fine. Still won't read it though in the 360K drive, it just says 0 sectors and gives up now instead of the errors I was getting, but I didn't turn analysis on.
 
Okay, I'm barking up the wrong tree. Are you trying to read the copy that you wrote in the 1.2M drive--or the original disk? Unless you started with degaussed disks, reading a disk written in a 1.2M drive using a 48 tpi drive will be, at best, problematical. The problem is that the 360K drive head sees a track that's twice as wide as the one that the 1.2M drive writes. A degaussed disk removes any traces of data previously written.
 
I know about the head width issue so never write 40 track disks on an 80 track drive.

I'd prefer to read a DSDD disk in the 360K drive, but it won't. It will however read it in the 1.2M drive, but at 300kHz. My goal would have been to archive disks from a 360K drive with the correct setting of 250kHz, but since it can't I suppose I can just use the imdu translate command to translate it after reading it in the 1.2M drive.
 
Can the 360K drive (using DOS commands) format and write a plain old DOS 360K disk successfully? Can that disk be read successfully in the 1.2M drive?
 
Alignment is the only thing that I can think of then. Perhaps the originals are a couple of mills offset from the orientation of the drive used to write the originals. You should certainly be able to see some sectors in any case.
 
Out of curiosity, what brand/models are each of the drives?

Here is an experiment you can try to see if this is the index "blind spot" that chuck is taking about.

For this experiment, we can't use ImageDisk, as it craps itself if it can not see the index during its analysis phase. Instead, lets use Trixter's disk2img http://www.oldskool.org/pc/disk2img .

Take one of your disks that was formatted in the Kaypro. Cut a small sticky square from a post-it note and carefully pace it over the jacket's index opening. (You don't want it sticking to the cookie). Then use disk2img to read in the image. Since it is not a DOS disk, you will need to manually specify the heads/sectors/tracks. Something like "disk2img b: test.img /t40 /s10 /h2

If it succeeds, try removing the piece of post-it note and see if it now fails. If that happens, then it is the "blind spot". If both fail, then it is something else such as alignment.
 
The system is a PC/AT 5170 with its stock drives. Drive A is a 1.2M and Drive B is a 360K with the asterisk in the corner. I'll try the test tonight!
 
If IMD saw no sectors at all, it's not the index problem. Typically, if sectors are numbered 1-10 on the track, the "blind spot" would have IMD seeing sectors 2-10. You might also try Anadisk.

But the symptom of "it used to see data on the disk, but now it doesn't" usually indicates a dirty head. Can happen quite a bit if you're using old media. Same for tapes.
 
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