This reminds me of my own attempts to read Acorn Atom programs from cassette tapes. I wrote a program to process wave files. Took me quite long to find a reliable method for recognizing the zero's and one's. But even that was not perfect and required some manual editing. For more details, see: http://www.iwriteiam.nl/D0301.html#20
Recovering “lost” treasure-filled floppy discs with an oscilloscope
41–50 of 55 posts
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#42It could be that the disc read head is more sensitive, or able to hover closer to the disc surface Unlike HDDs, floppy drive heads do actually rub on the surface of the media in normal operation. This is notable because repeated "scrubbing" in an attempt to statistically recover data[1] can make things much worse, especially if the media surface (or worse, the head) is already damaged. The attempt that bore some frui…
> I once wrote some code to recover degraded CD/DVD(+/-R) sectors by disabling the ECC of the drive How did you do this? Is there some SCSI/ATAPI command for this?
I'd also like to know. I tried to send those commands (SCSI I think?) to the drive, but it seemed to just ignore them. Heck, it seemed to ignore a huge portion of the different commands I tried to send it.
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#43Earlier quoted context omitted.
> I once wrote some code to recover degraded CD/DVD(+/-R) sectors by disabling the ECC of the drive How did you do this? Is there some SCSI/ATAPI command for this?
I'd also like to know. I tried to send those commands (SCSI I think?) to the drive, but it seemed to just ignore them. Heck, it seemed to ignore a huge portion of the different commands I tried to send it.
Sounds like "READ RAW". From memory it only works on certain drives - I want to say LiteOn but my memory is hazy.
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#44Earlier quoted context omitted.
I (American) agree with chungy; there is a strong convention that specifies floppy disks and compact discs. We could say that "disk" is the American spelling of "floppy disk" , but not that it is the American spelling of disc. I suspect that "disk" is used because it is shortened from "diskette", which wouldn't work at all if spelled "discette".
From https://en.wikipedia.org/wiki/Spelling_of_disc : By the 20th century, the "k" spelling was more popular in the United States, while the "c" variant was preferred in the UK. Consequently, in computer terminology today it is common for the "k" word to refer mainly to magnetic storage devices (particularly in British English, where the term disk is sometimes regarded as a contraction of diskette, a much later word…
And talking of interesting spelling, it's "Philips", not "Phillips".
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#45Earlier quoted context omitted.
I'd also like to know. I tried to send those commands (SCSI I think?) to the drive, but it seemed to just ignore them. Heck, it seemed to ignore a huge portion of the different commands I tried to send it.
Sounds like "READ RAW". From memory it only works on certain drives - I want to say LiteOn but my memory is hazy.
That matches with my recollection too. I remember getting a specific model of a LiteOn drive specifically to ensure that I had the ability to do this, both for data recovery and because some forms of copy protection abused disc read errors and made reading your own CDs a (kernel blocking) pain under linux. I think the source of `cdparanoia` [1] has some good examples.
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#46How does one go about studying and working in data archeology because this is really cool and seems like something that will be in greater demand as old media gets obsoleted and need to be retrieved to be preserved somehow.
Honestly I think myself and Chris (@scarybeast) would like to know too...! We've been learning as we go along.
Certainly I'd like to make contact with other people who are working in this area and compare notes... if anyone doing so is reading this, please do make contact. I'm on Twitter under the same username, Chris is @scarybeasts.
If you prefer email you can stick "@gmail.com" at the end of my HN username to get that :)
At the moment I'm working on cleaning up the remains of the DiscFerret project, and turning the project website into a general retrocomputing data recovery wiki.
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#47It could be that the disc read head is more sensitive, or able to hover closer to the disc surface Unlike HDDs, floppy drive heads do actually rub on the surface of the media in normal operation. This is notable because repeated "scrubbing" in an attempt to statistically recover data[1] can make things much worse, especially if the media surface (or worse, the head) is already damaged. The attempt that bore some frui…
> I once wrote some code to recover degraded CD/DVD(+/-R) sectors by disabling the ECC of the drive How did you do this? Is there some SCSI/ATAPI command for this?
What data you can get depends on the disc drive. DiscImageCreator [0] or the redump.org wiki [1] are good starting points.
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#48Earlier quoted context omitted.
It's just FM, on floppies known as "single density" mode: https://en.wikipedia.org/wiki/Frequency_modulation The common IBM PC and related formats use "double density" MFM: https://en.wikipedia.org/wiki/Modified_frequency_modulation
Interesting - I should really try to find the specifics on how AmigaOS stored its data. I'm guessing it's not MFM as the optional driver slash virtual device for reading IBM floppies required an MFM driver (thus implying MFM is not in use for standard AOS floppies). [edit] it actually IS mfm after all https://wiki.amigaos.net/wiki/Amiga_Floppy_Boot_Process_and_...
FYI, the MFM/Modified Frequency Modulation is also described in the original Shugart SA800/SA801 8-inch floppy diskette drives manuals.
The OEM Manual describes the basic MFM information and the Maintenance Manual contains the PCB layouts, logic information and the schematic diagrams. The first two links are to the OEM/Theory of Operation Manual and the third link is to the Maintenance Manual.
https://hxc2001.com/download/datasheet/floppy/thirdparty/Shu...
http://avitech.com.au/mm-files/dilog-dq419/SA800-801_Diskett...
http://bitsavers.informatik.uni-stuttgart.de/www.computer.mu...
BTW, I still have two SA800 drives from my old CompuPro 8/16 S-100 system that I thought would be nice to play with again when I had a moment but I've no 8" floppies either single or double density. Does anyone know where one can get some?
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#49It could be that the disc read head is more sensitive, or able to hover closer to the disc surface Unlike HDDs, floppy drive heads do actually rub on the surface of the media in normal operation. This is notable because repeated "scrubbing" in an attempt to statistically recover data[1] can make things much worse, especially if the media surface (or worse, the head) is already damaged. The attempt that bore some frui…
> I once wrote some code to recover degraded CD/DVD(+/-R) sectors by disabling the ECC of the drive How did you do this? Is there some SCSI/ATAPI command for this?
I found out how to use a vendor-specific command to read the raw data from the buffer of the drive before descrambling and ECC. Look up the "FriiDump" project for some more background information. I then patched the firmware in memory (that took a lot of work...) to cause regular read commands to return the raw data.
(Contrary to some of the other comments in this thread, the drive was actually an LG.)
Re: Recovering “lost” treasure-filled floppy discs with an oscilloscope
#50Oh wow, I did not realize that floppy discs used the same exact encoding that was used on tape drives of the era, e.g. the TI-99/4A [1]. The wave file in the article is the exact same sound I'd listen to as a child, loading programs from cassettes. Total coincidence -- I recently have been recovering games from my old TI-99/4A cassettes, also using an oscilloscope (the same model in fact; for no particularly good rea…
> the same model in fact
It could only be Rigol or Siglent. Fascinating though. I know how slow floppies are, but I wouldn't have imagined an oscilloscope to have the necessary resolution.