On Fri, 7 Oct 2005 06:56:49 +0200 "Nico de Jong" <nico at FARUMDATA.DK> wrote: Think about the density of the data on the diskettes (this is not a comment meant as a defense for the poor quality of magnetic media, just part of the discussion) A 1.44M floppy diskette puts a lot more data in a smaller area. The highest density 8" media I ever had was DSDD, or 720K on the big 8" surface. That's a LOT larger disk and hence a much lower density. Plus, the world of computers today has a lot more room for junk/commodity media. Anybody using floppy diskettes in 1976 had serious heavy-duty reasons for doing so. And those diskettes were EXPENSIVE. The disks you can get now at the Walgreens or a grocery store aren't the same. Further, there's no market for a high quality diskette, because 'high quality' customers have moved on to newer mediums. I got handed a new shrinkwrapped box of 8" diskettes recently at work. Finally everybody there is getting to know I am the person to hand stuff to. I'm soon to get a nice desktop HP pen plotter, too.

On 10/6/2005 at 10:26 PM Fred Cisin wrote: What surprised me is the way that the extra 3.5" data space was obtained. Always by boosting the data rate (mandating the need for new coating formulations). Never by increasing the number of tracks or changing the encoding method. The 2.88MB DSED diskettes were ridiculous--expensive AND unreliable. But point taken--the attractiveness of the floppy medium is that it's CHEAP. I've owned several LS-120 drives, but have never purchased a 120 MB SuperDisk. Cheers, Chuck

At 07:14 AM 10/7/2005, Scott Stevens wrote: What kind of emulator are you running that won't let you 'sys' to an image? :-) - John

It was actually closer to 1.2M. In fact the 1.2M IBM PC/AT format is almost exactly the same as a standard 8" format (it's the same data rate, same rotational speed, etc), the main difference being that the 8" drive has 77 cylinders, the 5.25" drive 80. However, I would rather have less data on a disk (and thus have to buy/carry/store more floppies) and be able to read it back later, than cram as much as possible onto a disk and find it's unreadable a few days later. I've pointed out several tinms here that the first disks I bought for my TRS-80 Model 1 cost me \pounds 5.00 _each_ (not a box of 10 or anything like that).. That mackine put 88K on each disk (single sided, 35 cylinders, FM (single desnity)). Point is, those disks are still readable 20 years later. I would like to be able to pay a reasonable amount -- say \pounds 5.00 to \pounds 10.00 for a 3.5" disk with the same quality level. Because my data is worth a lot more than that. Alas I have not. Not only because the newer drives are very poorly made and not properly documented, but also because most, if not all, of my machines can't use them. You try finding a DVD writer for a PERQ, or an HP41, or an HP9836, or.... Which model? I would love to find a 9862 with the original HP9810 interface module. But no chance of that (it would have to be local, there's no way I could afford to ship one anyway). Do far, the oddest pen plotter I've found is the 7470 Opt 003. That's an HPIL interface, it links up to the HP41, HP71, and HP75 calculators, amongst other machines. There's even an HP41 ROM module to support it. It's rather strange seeing a handheld calculator driving a full-size A4 plotter. The stranged HP plotter I own is not a pen plotter. It's the 7245A thermal printer/plotter. It's both a normal thermal printer _and_ a plotter -- in the latter mode it rolls the paper back and forth, moves the carriage across, and uses a special heater dot in the printhead to draw lines. Or so I am told. Mine doesn't work yet, which is why it's currently in a lot of bits on the bench. There are a lot of manuals (user and service) for HP plotters on http://www.hpmuseum.net , BTW. -tony

On Fri, 7 Oct 2005, Scott Stevens wrote: NO. The unformatted capacity is about 1.6M. Each track (77 tracks per side * 2 sides) can hold about 8 sectors of 1024 bytes each, or about 15 sectors of 512 bytes, or about 28 sectors of 256 bytes. The ONLY difference in format between a DSDD 8" drive and a "1.2M" 5.25 (which were originally created specifically as a drop in replacement for 8"!) is: 77 tracks per side on 8" V 80 tracks on "1.2M" 5.25" -- Grumpy Ol' Fred cisin at xenosoft.com

You can't do much about the width of a track, because head size is a physical constant of the drive. In principle current hardware could put flux transitions farther apart or some such, but I don't know whether the existing controller electronics can. It should be - but is it? I don't know floppy controller chips enough to say. However, if you pick up any good book on coding theory you can read all about adding ECC bits and then scattering data around so that (say) any arbitrary ten sectors could be lost or corrupted without rendering any data unrecoverable. ("Lost" is an easier case; it's easier to correct bits you know you don't have than bits you have but which you might have wrong.) For example, if you take (say) 13 sectors of 256 bytes each and think of them as an array of 13 by 2048 bits, you can then apply ECC along the 13-bit dimension, adding 5 error-correction bits, to get 18 sectors of 256 bytes each, with the ability to correct any N sectors that are wrong, for some value of N (which I'm not a good enough coding theorist to know, but I'd guess is around 4 to 6). Repeat for each track and you've lost 5/18 of your space but you've got the ability to lose up to N sectors per track without losing any data. More complex schemes can spread data out even more.... /~\ The ASCII der Mouse \ / Ribbon Campaign X Against HTML mouse at rodents.montreal.qc.ca / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

On Fri, 7 Oct 2005, Scott Stevens wrote: Redundant filesystems can help substantially with localized damage. Unfortunately, they won't help in cases where the entire disk craps out. FAT filesystems have two copies of the F.A.T. But,... 1) What is the worst possible place to put the second copy? (adjacent to the first) 2) For a redundant filesystem to achieve its advantages, there must be software that can recognize problems, and switch to alternate copies. There actually exist some floppy R.A.I.D. implementations! Depending on configuration, that could provide full recoverability, if only one disk fails at a time.