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<H3 align="left"><img src="../../gx/dennis/qbubble.gif"
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height="50" width="60" alt="(?) " border="0"
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>CRC errors on floppy disks</H3>
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<p><strong>From "David"
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</strong></p>
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<p align="right"><strong>Answered By Dan Wilder, Heather Stern, John Karns
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</strong></p>
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<P><STRONG>
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Thankyou for taking the time to read this. I am marked down as one of
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the university
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geeks, and it is coming around to the time to hand in
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essays/dissertations etc.
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Many people have put misplaced faith in the reliability of floppy disks.
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Is there any tool for linux, which will allow me to ask the floppy
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driver in the kernel to keep trying, so I can put together the
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statistically "best" hex dumps,or extract raw text from Word docs etc.
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Dan]
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'Fraid I can't offer any way to recover the data once it's
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lost to bad sectors, tho no doubt some way is possible.
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</blockQuote>
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<blockQuote>
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Instead I'd like to offer the format script I use for floppies
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before I'll trust 'em with my data. It culls out a lot of
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floppies, and I find that floppies which once passed, after sitting
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a few years on the shelf, will often no longer do so.
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</blockQuote>
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<blockQuote>
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User who runs this must have write permission to <TT>/dev/fd0h1440.</TT>
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Requires mtools. Watch out, some distributions may obsolete
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fdformat in favor of superformat.
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</blockQuote>
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<p align="center">See attached <tt><a href="../misc/tag/goodfloppy.sh.txt">goodfloppy.sh.txt</a></tt></p>
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<P><STRONG>
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<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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Today I resuced a 6 page essay 10hrs before it was due,
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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The easiest way to do this sort of thing (I used to do it too) is
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</blockQuote>
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<blockQuote>
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1. use dd to extract a raw image of floppy disks. This is sufficiently
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reliable that it's now the <EM>normal</EM> way I mount floppies on my laptop.
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</blockQuote>
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<blockQuote><CODE>
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dd if=/dev/fd0 of=/usr/local/floppy/student-name-ddmmyy.144 bs=18k
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</CODE></blockQuote>
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<blockQuote>
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In case you're curious 18k is the standard blocksize of a single track,
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so this is the "native" amount of bits the floppy read heads want to read
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anyway. It should be fastest and have the best chance of getting all the
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rescuable bits.
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</blockQuote>
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<P><STRONG>
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<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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I already take a copy, as I am not the only geek with enough time, and I
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don't want to write anything back to a damaged floppy. Thanks for the
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advice with bs=18k I will use that next time.
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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Yep, it's about 8 times faster with that set.
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</blockQuote>
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<blockQuote>
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2. the rescue
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</blockQuote>
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<blockQuote>
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<ol type="a">
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<li> See if Linux will mount the raw image - as it may be more reliable
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than a floppy whose cookie got slow (in other words a straight read
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is better than lots of little seeks)
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<li>
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if not, use 'strings' on the resulting file, noting that some of the
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ASCII bits will just be raw strings of letters from headers and things
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(e.g. "GIF89A")
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</ol>
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</blockQuote>
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<blockQuote>
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Ugly but better than nothing during Finals Week.
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</blockQuote>
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<P><STRONG>
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<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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Most disks that I have come across mount OK, but if all else fails, I
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have all night, a copy of Peter Nortons PC Programmers Bible (plenty on
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disk structure, FAT layout etc), and the promise of as much beer as I
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can drink from the hapless author.
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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I got a full case of Henry Weinhardt's Root Beer once. The gal knows I
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don't normally drink alcohol. No wait, that wasn't in college, that
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was in the corporate world. I got some cool coffeecups... uh no, that
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was in the corporate world too. Nevermind
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<IMG SRC="../../gx/dennis/smily.gif" ALT=";P"
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height="24" width="20" align="middle">
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</blockQuote>
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<P><STRONG>
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<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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...but the 200
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words held on the bad sectors were well and truly gone.
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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Sorry. Once there's scratch marks there, they lose.
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</blockQuote>
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<P><STRONG>
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<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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This is not so good, what I was really after is someway to attempt to
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make best guesses for what is in those bad-sectors. I know that it
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sounds difficult, but I am looking for something between Scandisk for
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windows, and professionals in a clean-room!
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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We have dosfsck, of completely unknown reliability, but you're welcome
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to try it too. What the heck.
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</blockQuote>
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<blockQuote>
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Short of trying the floppy again in a floppy bay with different alignment,
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basically you either got the bits, or you didn't. And indeed, you could
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try that (though it submits the poor dented floppy to N more visits by
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drive gear) and see if the md5sums of any of the dd images are different.
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If so, scour the tweaked ones for anymore bits you can rescue also. Don't
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hold your breath, but you'll have earned the extra brewskies if it works.
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</blockQuote>
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<blockQuote>
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Clean-room efforts are basically able to micro-position the heads in the
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hopes of seeing the last two to five major writes. Ontrack does such
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recovery, but I dunno if they do floppies at all. I suspect not.
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</blockQuote>
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<P><STRONG>
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<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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Is there
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anything better than dd conv=noerror, that will allow me to access these
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dodgey disks from linux. I am kind
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of looking for something like Spinrite by Steve Gibson, but I would like
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to have it
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for linux, and for free.
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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spinrite worked on IDE drives, not floppies.
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</blockQuote>
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<blockQuote>
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If you want a hex editor in the spirit of Norton Disk Editor, try lde, but
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frankly, I'd use 'hexedit' (a curses-terminal program) on a dd image of the
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floppy before I'd consider that ... to reduce the amount of usage tried on
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an already poor-condition floppy.
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</blockQuote>
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<blockQuote>
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Oh yeah, and much as ZIP and LS-120 bays are less popular, their cartridges
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are <EM>much</EM> more reliable than standard floppies, and CD-RW even more so
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(but sadly CD-RW cannot be written to directly, just burned as a complete
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image -- and DVD-RAM drives are still not in the normal-consumer price range,
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plus they're rare even in the Silicon Valley).
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</blockQuote>
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<P><STRONG>
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<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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Forget DVD-RAM <TT>/</TT> CD-RW. Most people use floppies to move work between
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computer labs with internet, and our rooms without. Nobody in college
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has administritave access to the networked PC's, and the amount of
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people who simply use a floppy to avoid copying files around is scary.
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We have just got new ZIP-250's, so things should look up for next term!
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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Well, definitely looking up there!
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</blockQuote>
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<blockQuote>
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Oh yeah, remind people not to leave their floppies (or cartridges) lying
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around in the noonday sun on the car shelf, or other places where they
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would get toasty and you wouldn't put VHS tapes. It's basically the same
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type of media with the same type of susceptibility to heat damage.
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</blockQuote>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [John]
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I usually keep floppies in the box they came in or in a small plastic bag.
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If you examine one, you'll see that they have an open slot at the top edge
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where the sliding metal access door is. When left out in the open air,
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floating particles enter and adhere to the surface of the plastic disk
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inside.
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</blockQuote>
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<blockQuote>
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Zip disks don't seem to have such a comparatively large opening in the
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housing as floppies, which may a reason they fare better. But one is very
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well advised to keep all magnetic media, including tapes, in a protective
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case or other dust barrier. I've noticed that plastic materials seem to
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act like magnets for carbon dust, which when smudged leaves a grease spot
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on the plastic material.
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</blockQuote>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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I am reminded of a time that we posted somebody's ruined floppy to the
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student-center wall... pried loose of its plastic envelope so the round
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disc was revealed, dent and all. Caption: "Don't do this to
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your floppy". I forget exactly what did it. The crease wasn't much -
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maybe someone sat on it, I dunno. But it was definitely dead.
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</blockQuote>
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<blockQuote>
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I don't know if your policies are about guest-level access only or you
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create actual accounts for people there. If the latter then some sort of
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share server (samba or perhaps one of those file-appliance boxes that have
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gotten so popular) which looks like the same drive letter on all networked
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boxes, would get people to use that instead. I like H: for "home" but
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your tastes may vary. Combined with the permissions-by-login behavior
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samba can provide it's not too bad. You might not want to make it automatic
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or perhaps people will abandon logged in machines and mess up each other's
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space. And not everyone would use it, perhaps they want to take some work
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back to the dorm with them. They might even get them out of sync. (I think
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the MSwin buzzword for doing it the right way is "My Briefcase" but don't
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quote me, I could be wrong these days. Here in linux we use rsync, and have
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to be careful about the commands we give it, too.) In other words it has
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its own headaches... but it's not as unreliable at the bits level as floppies
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are.
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</blockQuote>
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<blockQuote>
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I think that's about as much as Linux can really do for throwing software
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against what is basically a hardware and a clue-ware problem, but there
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ya go. Best of luck in the efforts!
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</blockQuote>
|
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<P><STRONG>
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|
<IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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>
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|
Thanks in advance
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</STRONG></P>
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<P><STRONG>
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|
David
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</STRONG></P>
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<P><STRONG>
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P.S. If you publish my e-mail can you obscure it somehow. My uni acct is
|
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so far spam-free and I would like to keep it that way.
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</STRONG></P>
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<blockQuote>
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<IMG SRC="../../gx/dennis/bbub.gif" ALT="(!)"
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HEIGHT="28" WIDTH="50" BORDER="0"
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> [Heather]
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Yes, we can anonymize you. If this stays short enough for Tips we'll put
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"anonymous" instead of your email, and if enough of the Gang chime in it
|
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may be a TAG thread, where emails are not published at all unless directly
|
|
related to the solution (e.g. project maintainers).
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</blockQuote>
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<!-- *** BEGIN copyright *** -->
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<H5 align="center">This page edited and maintained by the Editors
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of <I>Linux Gazette</I>
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<a href=""
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>Copyright ©</a> 2002
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<BR>Published in issue 77 of <I>Linux Gazette</I> April 2002</H5>
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<H6 ALIGN="center">HTML script maintained by
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<A HREF="mailto:star@starshine.org">Heather Stern</a> of
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Starshine Technical Services,
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<A HREF="http://www.starshine.org/">http://www.starshine.org/</A>
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</H6>
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