On Wednesday 30 July 2008 07:38:07 pm Chuck Cole wrote: > > -----Original Message----- > > From: tclug-list-bounces at mn-linux.org > > [mailto:tclug-list-bounces at mn-linux.org]On Behalf Of Josh Paetzel > > Sent: Wednesday, July 30, 2008 7:41 AM > > > > Unfortunately digital recordings don't tolerate degradation at all. A > > single bit error is enough to make a binary file unusable....whereas you > > can lose a vast amount of analog information and still make out what song > > you're listening to. > > My engineeering knowledge and experience differs somewhat from your > summaries here. > > Even floppies used sector-wise CRC, so errors are usually detectable even > if one has not used an error detecting and correcting shell like zip, etc. > > Single bit errors per sector are usually detectable and often correctable. > Storing without an integrity check layer is/was truly unwise. Modern > drives automate much of that and hide the details from us most of the time. > We had to do such things manually in the days of CP/M before MSDOS and PCs > emerged. Similar precautions were observed in the minicomputer world then. > > Degradation of a digital signal begins as a signal-to-noise-ratio (SNR) > reduction, and that may have a big margin before becoming actual bit > errors. > I cleaned the heads in my floppy drives reasonably often to assure a decent > SNR, and I used top brands of media as well: perhaps these factors have > much to do with my general success in longevity of floppies. > > > Case in point, 20 years ago cassette tape sucked ass as a medium for > > music, but it was livable. Using cassettes for digital storage however > > was so incredibly painful you only tolerated it if you had no other > > choice. > > There was no other personal computer choice before 8 inch floppies. Media > choice was important, as was proper signal waveform. When set (and checked) > to have good waveforms, the recording and playbacks were quite reliable, > but SLOW. I found that it was important to verify that a recorder could > and did meet NAB standards. I may still have the NAB calibration tapes I > bought, and do have a very good Sony 3-head mono recorder that easily met > the specs. Cheap recorders produced waveforms that never had decent "eye > patterns", so it's no wonder some recordings were "not archival quality". > I had short-term problems with crummy recorders. > What personal computer predated the 8" floppy? > > There are tape mediums that have shelf lives in the 30 year range, > > unfortunately floppies were not designed to have a long shelf life. > > I'm curious: is that just a supposition, or do you have any documention of > that? I think data of the day I had would indicate that the medium was > designed for best archival capability, but I didn't save any of that stuff. > > > believe I was testing 5.25" floppies in 1998 when I was preparing to move > > from Michigan to Minnesota. They had been stored in a cool dry dark > > place and were for the most part all junk. I think they were about 6 > > years old at that point. Maybe a tad less. > > Not clear that you took any precaution at all to assure longevity. I have > only "spot checked" a few of my many floppies from c1984 and maybe older, > but have had little difficulty with reading data, doing surface scan > checks, and even an occasional re-recording in place to assure good SNR. I > ran a club library and still have several hunderd pounds of 5.25 floppies > in a good steel case "file cabinet". Some very dull rainy day, I'll move > the "good stuff" over to CDs and get rid of the floppies. > > My experience differs greatly from yours. I think the old error-handling > routines for floppies were/are available in source code form in Z/CPR, the > open-source version of CP/M... haven't looked in many years, tho. > > > Chuck > The documentation varies depending on it's age. Documentation from 20 years ago suggests a properly stored floppy may have a shelf life of 30 years. Documentation from today suggests floppies have a shelf life of a couple years. Perhaps the disparagy in documentation is rooted in either the widespread discovery that the shelf life isn't as long as it was once thought? Or perhaps proper storage is difficult? It's been a long time since I've had to deal with floppies on any sort of consistant basis, but I don't ever recall considering them a reliable storage medium on any platform. I'm not sure I took any precautions to ensure the longevity of the floppies I put out to pasture either, other than being careful where I stored them. It's possible they were exposed to large magnetic fields, it's equally possible my floppy drives controllers or cables were junk. It's also possible that floppies don't last as long as one might think. -- Thanks, Josh Paetzel PGP: 8A48 EF36 5E9F 4EDA 5A8C 11B4 26F9 01F1 27AF AECB -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 195 bytes Desc: This is a digitally signed message part. Url : http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20080730/add1666c/attachment.pgp