{"id":286,"date":"2020-08-18T19:23:47","date_gmt":"2020-08-18T20:23:47","guid":{"rendered":"http:\/\/www.linux-tutorial.info\/?page_id=77"},"modified":"2020-08-22T19:26:01","modified_gmt":"2020-08-22T20:26:01","slug":"this-is-the-page-title-toplevel-121","status":"publish","type":"page","link":"http:\/\/www.linux-tutorial.info\/?page_id=286","title":{"rendered":"Floppy Drives"},"content":{"rendered":"\nFloppy Drives<\/title>\n<p>\nA customer once called in to tech support about a system that would not\n<glossary>boot<\/glossary>. For some unknown reason, the system crashed and\nwould no longer boot from the hard disk. It got to a particular point in the\nboot process and hung. Even an old copy of the <glossary>kernel<\/glossary> hung\nin the same way.\n<\/p>\n<p>\nFortunately, the customer had an emergency <glossary>boot<\/glossary>\nfloppy that enabled him to boot and gain access to the hard disk. The customer\nstuck the floppy in the drive and pressed the reset button. After a few\nseconds, there were the normal messages the system presented at boot up. For the\nmoment, things looked fine. Suddenly the messages stopped and I could hear over\nthe phone how the floppy drive was straining. It finally came up with the\ndreaded “floppy read error.” Rather than giving up, I decided to try it again.\nSame thing.\n<\/p>\n<p>\nAt that point I started to get concerned. The hard disk booted, but the\n<glossary>kernel<\/glossary> hung. The floppy booted, but somewhere in the middle\nof loading the kernel, there was a bad spot on the floppy. This was not a good\nthing.\n<\/p>\n<p>\nThe floppy disk was brand new and the customer had tested it out immediately\nafter he had made it. The most logical thing that caused this problem was\nputting the floppy too close to a magnetic field. Nope! That wasn’t it, either.\nThe customer had been told to keep this floppy in a safe place, and that’s what\nthe customer did.\n<\/p>\n<p>\nWhat was that safe place? The customer had tacked it to the bulletin board\nnext to the monitor, not through the hub or at one of the corners, but right\nthrough the floppy itself. The customer had been careful not to stick the\npin through the media access hole because he was told never to touch the floppy\nmedia itself.\n<\/p>\n<p>\nIn this section, I’m going to talk about floppy disks, lovingly referred to\nas floppies. They come in different sizes and shapes, but all floppies serve\nthe same basic functions. Interaction with floppies can be a cause of great\nheartache for the unprepared, so, Im going to talk about what they are like\nphysically, how they are accessed, and what kinds of problems you can have with\nthem.\n<\/p>\n<p>\nAlthough they hold substantially less data than hard disks, floppies appear\nand behave very much like hard disks. Like hard disks, floppies are broken down\ninto sectors, tracks, and even cylinders. Like hard disks, the number of tracks\ntells us how many tracks are on a given surface. Therefore, a floppy described\nas 40 tracks (such as a 360KiB floppy) actually contains 80 tracks, or 40\ncylinders.\n<\/p>\n<p>\nOther common characteristics are the <glossary>header<\/glossary>\nand trailer of each <glossary>sector<\/glossary>,\nwhich results in 571 bytes per sector, 512 of those being data. Floppy disks\nalmost universally use MFM data encoding.\n<\/p>\n<p>\nLinux floppy drivers support a wide range of floppies: from the ancient 48\ntracks per inch\/8 sectors per track, 5.25″ floppies to the newer 135 tracks\nper inch\/36 <glossary>sector<\/glossary> per track, 3.5″ floppies that can hold\nalmost 3Mib of data. More commonly however, the floppy devices found on systems\ntoday are somewhere in between these two types.\n<\/p>\n<p>\nBecause they are as old as PCs themselves, floppies have changed little\nexcept for their size and the amount of data that can be stored on them. As a\nresult, very few problems are encountered with floppies. One most common problem\nis that customers are unsure which floppy device goes to which type of drive.\nSometimes customers do know the difference and try to save money by forcing the\nfloppy to format in a density higher than it was designed for.\n<\/p>\n<p>\nThe truth of the matter is, you <em>can’t<\/em> format floppies higher than\nyou’re supposed to, that is, higher than the manufacturer specifies. To some\nextent, you might get away with punching holes in single-sided floppies to make\nthem double-sided. However, forcing a floppy to a format at a higher density (if\nit works) isn’t worth risking your data.\n<\/p>\n<p>\nTo understand why this is so, I need to talk about the concept of coercivity,\nthat is, how much energy (how strong the magnetic field) must be used to make a\nproper recording on a disk. Older floppies had a lower coercivity and therefore\nrequired a weaker magnetic field to hold the signal; that is, less energy was\nrequired to “coerce” them into a particular pattern.\n<\/p>\n<p>\nThis seems somewhat contradictory, but look at it another way. As densities\nincreased, the magnetic particles got closer together and started to interfere\nwith each other. The result was to make the particles weaker magnetically. The\nweaker the particles are magnetically, the stronger a force was needed to\n“coerce” them into the proper patterns to hold data. Therefore, high-density\ndisks have a higher coercivity.\n<\/p>\n<p>\nAs the capacity of drives increased, the tracks became narrower. The low\ndensity 5.25″ floppies had 48 tracks per inch and could hold 360KiB data. The\nhigh density 5.25″ floppies have twice as many tracks per inch and can hold\n1.2MiB (the added increase is also due to the fact they have 15 sectors per track\ninstead of nine). Because there are more tracks in a given space, they are\nthinner. Problems arise if you use a disk formatted at 360KiB a 1.2MiB drive.\nBecause the 1.2 <glossary>MiB<\/glossary> drive writes the thinner tracks, not all\nof the track of the 360KiB is overwritten. This may not be a problem in the\n1.2MiB drive, but if you ever try to read that floppy in a 360KiB, the data\nwill run together. That is, the larger head will read data from more than one\ntrack.\n<\/p>\n<p>\nFormatting a 360KiB as a 1.2MiB usually fails miserably because of the\ndifferent number of tracks, so you usually cant get yourself into trouble.\nHowever, with 3.5″ floppies, the story is a little different. For both the 720KiB\nand 1.44MiB floppies, there are 80 tracks per side. The difference is that the\n1.44MiB floppies are designed to handle 18 sectors per track instead of just\nnine. As a result, formatting <i>appears<\/i> to go well. It is only later that\nyou discover that the data is not written correctly.\n<\/p>\n<p>\nThe reason for this is that the magnetic media for the lower-density 720KiB\nfloppies is less sensitive. By formatting it as 1.44MiB, you subject it to a\nstronger magnetic field than you should. After a while, this “overdose” causes\nthe individual magnetic fields to begin to interfere with one another. Because\nhigh-density, 1.44MiB floppies cost a few cents apiece, it’s not worth risking\ndata by trying to force low-density to high-density to save money.\n<\/p>\n<p>\nWhile I’m on the subject of money, note that buying unformatted floppies to\nsave money is becoming less and less the smart thing to do. If you figure that\nformatting floppies takes at least two minutes apiece and the cost difference\nbetween a package of ten formatted floppies and ten unformatted is $2, then it\nwould only make sense (or cents) to have someone format these if they were\nmaking only $6.00 an hour. Rarely does a company have someone whose sole job is\nto format floppies. That job usually falls on those people who use them and most\nof them get more than $6.00 an hour. Therefore, you may as well buy the\nformatted floppies.\n<\/p>\n<p>(I actually did some consulting work for a company whose president insisted\nthat they buy <i>unformatted<\/i> floppies. Because the only people who used the\nfloppies were his programmers and system administrators, they earned more than\n$6.00 an hour. In one case, I calculated that turning a package of 10\nunformatted floppies into formatted floppies worked out to costing twice as much\nfor the unformatted as for the formatted ones. That didn’t phase him a bit\nbecause the system administrators were on salary and were paid no matter what.\nBy saving the few dollars by buying unformatted ones, his profit margin looked\nbetter, at least on paper.)\n<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Floppy Drives A customer once called in to tech support about a system that would not boot. For some unknown reason, the system crashed and would no longer boot from the hard disk. It got to a particular point in … <a href=\"http:\/\/www.linux-tutorial.info\/?page_id=286\">Continue reading <span class=\"meta-nav\">→<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-286","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages\/286","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=286"}],"version-history":[{"count":1,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages\/286\/revisions"}],"predecessor-version":[{"id":562,"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=\/wp\/v2\/pages\/286\/revisions\/562"}],"wp:attachment":[{"href":"http:\/\/www.linux-tutorial.info\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=286"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}