Re: Floppy rescue: media separation from hub
On Fri, Sep 08, 2017 at 12:46:02PM -0700, Chuck Guzis via cctalk wrote: [...] > This is particularly true if you use a whole-track reader than can read > tracks without regard to index. > I don't know about Amiga, however. The Amiga's native disk format assumes whole-track reads and writes anyway: the sectors are bunched together with just a single gap between the first and last sector, and the tracks are not aligned to the index pulse.
Re: Floppy rescue: media separation from hub
An uninteresting answer but is this proprietary data or something another collector may have and could provide? null
Re: Floppy rescue: media separation from hub
On 09/08/2017 01:42 PM, Fred Cisin wrote: > "Normal" "simple" PC-type read, such as > COPY source destinat > CAN have a big problem. If you put the bub back on, so that index is > right in the middle of a sector, then that sector can't be read (with > NEC-type FDC, unless you "mask-off" the index signal). Likewise, if > index is too close before the beginning of the sector. NEC-type FDC > does not want to read/write immediately after index. So mask off the index line and you'll be fine. --Chuck
Re: DIY crude digital alignment disk (Was: Floppy rescue: media separation from hub
One more concern: Be very careful centering it! If the cookie is off-center, relative to the hub, then tracks won't be in the right positions. 3.5" disks are 135 tracks per inch, so an imperfection of 1/5 mm is more than an entire track space! Actually, that could be VERY useful! On a "normal" disk, if the hub is off-center, then two positions of each track will have correct radial alignment, and the rest will be off. If, for example, sector 2 reads correctly, then it should be close to correct between sectors 6 and 7 of a 720K, or 11 on a 1.4M. Actually, only PART of sector 2 will be correctly aligned, but the rest of it should be close enough. If another drive reads sector 3 correctly, instead, then it is out of alignment. If a third drive reads sector 6 or 7 (between 2 and 3 on 1.4M) then it is halfway between the other two drives. You would not know which direction drive #2 or #3 are off, but by trial and error, you could go each way, until it works, and then save the information about which way it had been off. So, it would be a VERY crude version of the Dysan Digital Diagnostic diskette, at least in terms of radial alignment. 1.4M would be preferable, due to the larger number and physically shorter sectors, although an odd number of sectors adds "half-spacing" on the opposite side of the track. You would need to try a known good (radial aligned) drive to determine which sector (or range of sectors) is correctly positioned. Then need to take another drive for which you are willing to change or corrupt the alignment, and by trial and error find which direction it is off, to record whether sectors before or after the "correct" sector(s) are too far in or out. If you MEASURE how far you need to move it, then you could calibrate it. Then, to get a crude alignment of a drive, just list which sector(s) will read (median for ranges), and look up direction and distance. OB_ridiculous-extensions: Make numerous off-center disks. Create a consistent format for the calibration data. For mass production, modify a drive to be able to move the hub clamp known distances off center of the spindle. (could be set different for different tracks, and calibration data could be written to the sectors themselves!) Create software that checks which sectors are readable on a track, accesses the appropriate calibration data, and displays color graphic images for common drive types, showing how to adjust radial alignment, and interactively guide semi-skilled users through making the adjustments. How many things are wrong with this dumb idea? -- Grumpy Ol' Fred ci...@xenosoft.com
Re: Floppy rescue: media separation from hub
On Fri, 8 Sep 2017, Chuck Guzis via cctalk wrote: Yes, they were glued. Sometimes you can look carefully at the hub and the cookie and match up remaining glue deposits. In the case of a simple PC-type read, the position of the index doesn't really matter for reading--as long as the sector headers are correct, you're fine. "Normal" "simple" PC-type read, such as COPY source destinat CAN have a big problem. If you put the bub back on, so that index is right in the middle of a sector, then that sector can't be read (with NEC-type FDC, unless you "mask-off" the index signal). Likewise, if index is too close before the beginning of the sector. NEC-type FDC does not want to read/write immediately after index. This is particularly true if you use a whole-track reader than can read tracks without regard to index. A whole track read, that ignores index would do just great. WD 179x has a usable TRACK READ It should be easy to read Amiga using WD 179x. Unfortunately, NEC didn't implement THAT. They provide a "READ MULTIPLE SECTORS", instead of "READ TRACK". DISK2FDI, ADFREAD play some strange games (such as switching drives in the middle of a read!) to trick the NEC into reading track. I don't know about Amiga, however. Amiga seems to be MFM, without IBM/WD style sector headers. Amiga appears to read track and then parse sectors in memory. -- Grumpy Ol' Fred ci...@xenosoft.com
Re: Floppy rescue: media separation from hub
On 09/08/2017 11:51 AM, John Foust via cctalk wrote: > > When attemping to read an old Amiga floppy, the magnetic media > separated from the metal hub. Were these originally glued? > > Assuming I can find a way to re-affix the media to the hub, how many > guesses as to the proper alignment might I need to make? After all, > the metal hub has an index slot and the media was formatted in > relation to that. > > Is the answer different for a PC floppy? Yes, they were glued. Sometimes you can look carefully at the hub and the cookie and match up remaining glue deposits. In the case of a simple PC-type read, the position of the index doesn't really matter for reading--as long as the sector headers are correct, you're fine. This is particularly true if you use a whole-track reader than can read tracks without regard to index. I don't know about Amiga, however. --Chuck
Re: Floppy rescue: media separation from hub
On Fri, 8 Sep 2017, John Foust via cctalk wrote:
When attemping to read an old Amiga floppy, the magnetic media
separated from the metal hub. Were these originally glued?
Assuming I can find a way to re-affix the media to the hub, how many
guesses as to the proper alignment might I need to make? After all,
the metal hub has an index slot and the media was formatted in
relation to that.
Is the answer different for a PC floppy?
Partially.
The PC has a gap after index, and then a smaller gap between each
sector.
With the PC, the index is only needed during formatting, BUT, even during
reading, the NEC-style FDC goes "blind" momentarily right after index.
Thus, any sectors too soon after index are "not found". However, if you
encounter that problem with disks that are otherwise PC readable, you can
"mask"/interrupt the index line of the floppy cable. On many old 5.25"
drives (NOT including Teac 55), you can even just put a write-protect tab
over the index access hole of the floppy jacket (on Teac and a few others,
the drive is dependent on seeing index to be "ready"). Interrupting the
cable is not without a few minor complications. For example, if you ask
for a specific sector, the PC (INT13h) normally waits through a few
revolutions, then reports error code 4 ("Sector Not Found"); but, if
you've interfered with the index, then it will come up with error code 128
("Drive Not Ready") instead.
Reading PC sectors without masking will work fine, except for any that
straddle, or are too soon after, index. Some disk formats, such as
Cromemco have very tight inter-sector gaps, and reading with PC can be
less unreliable.
On the Amiga, there are little or no gaps between sectors. It essentially
does a track read/write and then parses in memory, instead of searching
for individual sectors to read. It probably relies on index to decide
when to start reading. It may be possible to write some code on the Amiga
to read a track, and then splice from end to beginning to patch it.
What are you imaging it with?
If you could read the entire track (such as with a WD 179x), ignoring
index, and then splice material from the end to the beginning as
necessary, then you would be OK.
At least SOME flux-transition boards (I KNOW CP Option Board does) require
the index pulse to operate. (THAT made it trivial to create a disk that
would choke Copy-II-PC-OptionBoard software, but could be copied [losing
the protection] with DISKCOPY)
If you can read "more than a track", then you can manually find and mark
where the start of track is.
The weird hacks to fool the NEC into reading track (in order to read Amiga
on PC) might or might not work with index masked. Without it masked, your
placement of index will have to be accurate.
--
Grumpy Ol' Fred ci...@xenosoft.com
Floppy rescue: media separation from hub
When attemping to read an old Amiga floppy, the magnetic media separated from the metal hub. Were these originally glued? Assuming I can find a way to re-affix the media to the hub, how many guesses as to the proper alignment might I need to make? After all, the metal hub has an index slot and the media was formatted in relation to that. Is the answer different for a PC floppy? - John
