Voila pourquoi les D7 déconnent

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  Xanxi

  28 mars 2012 à 13h10 #10417

  Depuis 5 – 6 ans, je n’ai quasiment aucune disquette qui garde ses données correctement plus d’une semaine ou deux, bien que j’ai de nombreux lecteurs DD et HD, certains neufs ou révisés, ET un stock de disquettes HD de marque neuves.

  Pourtant des D7 copiées et recopiés de marque pourrie qui datent de 1990-1994 sont toujours nickel.

  Voila ici une vraie explication technique copiée d’un site Mac:

  To clear up the persistent confusion and superstition about 800K vs. 1.44MB media, here’s the correct story: There is about a ten percent difference in the magnetization thresholds (called « coercivity ») for the two media, with the 800K stuff having the lower value. If you want to get technical, 800K media have a nominal coercivity of 650 oersteds, versus 720 – 730 oersteds for 1.4MB media. So, 800K drives may find it difficult to write on 1.44MB media. However, ten percent is not a large difference, and in fact, is about the same as normal variations within a batch from a given manufacturing run. Plus, coercivity varies with temperature, too. So, the two media are not as wholly incompatible as lore has it. However, if a 1.4MB disk has ever been written on by a 1.4MB drive (and this includes formatting), an 800K drive’s weaker write fields may not be strong enough to reliably over-write the existing data, and you’ll have flaky behavior (particularly if you’re unlucky enough to have a drive with write currents at the low end of the spec, trying to write on a floppy with coercivity at the high end of spec). But if the floppy is virgin, you’ll rarely see any problems at all. You can « re-virginize » floppies if you have a good demagnetizer handy. Now, if you go the other way, by melting or punching (don’t drill!) an extra hole to trick drives into thinking an 800K floppy is really 1.4MB, there’s no problem with the drive’s ability to flip magnetizations properly. However, the higher density is achieved by packing adjacent bits more tightly together on a given track (but the number of tracks per side is the same — 80 — for 400K/720K/800K/1.4MB media), and the lower density media may not have fine enough particles to do the job well (and the lower magnetic field strength of those particles further degrades margin). That’s why many advise against doing this operation.

  100% Amiga Classic
  BOING!!!!

  

  Kris

  28 mars 2012 à 15h33 #159798

  Interesting technical article !!