124 lines
6.0 KiB
Plaintext
124 lines
6.0 KiB
Plaintext
The following is an exerpt from a text file written/complied by one
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A.D. Longton of Rockville, MD. I have omitted the discussion of how
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to make a 1.44M disk from a 720K disk with a soldering iron since I
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don't want to be a party to furthering that practice. I did, however,
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find the remainder of the information quite interesting and have
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included it here. As You can see, it comes directly from the
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'brain trust' at Big Blue and may tend to lend some measure of credibility
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to what I've been saying all along. The original file was dated 5/10/89,
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I'm not sure when the information spewed forth from Boca Raton.
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-[Steve]- (tm)
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-------------------------------------------------------------------------------
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3.5" DISKETTE FORMATS
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Kevin Maier
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IBM Corporation
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Boca Raton, Florida
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"Reprinted by permission of the
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IBM Personal Systems Technical Journal."
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Page 42, issue 2, 1989
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"The original recommendations about the proper formatting and use
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of PS/2 diskettes have undergone revision. This article explains
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why the recommendations have changed.
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THE ORIGINAL CAUTION
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Personal System/2 shipping cartons include a sheet of paper that
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cautions users not to format a 2.0 MB diskette to 720 KB, because
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the diskette becomes unusable and should be discarded.
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This caution was issued because of the physical properties of 720
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KB diskettes versus 1.44 MB diskettes. The 720 KB format uses a
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higher write current, and the 1.44 MB format uses a lower write
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current. To accommodate the higher write current, the oxide
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coating on a 1.0 MB (720 KB formatted) diskette is denser than the
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oxide coating on a 2.0 MB (1.44 MB formatted) diskette.
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When you format a 2.0 MB diskette to 720 KB, you apply the higher
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write current to the less dense oxide coating. The hardware
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developers originally felt that this meant the 720 KB formatting
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pattern is written too deeply into the 2.0 MB oxide coating,
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causing intermittent data errors and unreliable use. Furthermore,
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the developers felt that if you attempted to reformat the diskette
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to 1.44 MB, which uses the lower write current, the 1.44 MB format
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would not completely write over the "deeper" 720 KB format.
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Therefore the developers' recommendation was to discard a 2.0 MB
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diskette that was formatted to 720 KB.
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THE SUBSEQUENT FINDINGS
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[aka a RETRACTION]
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Since the time that this caution was issued, the developers have
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performed additional testing, and have concluded that there is no
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need to discard a 2.0 MB diskette that was formatted to 720 KB.
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It is still true that a 2.0 MB diskette formated to 720 KB will
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cause intermittent data errors. However, the latest assessment is
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that you will be able to reformat the diskette to 1.44 MB and use
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it reliably after that.
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The same logic applies to a 1.0 MB diskette formatted to 1.44 MB.
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You cannot use it with the 1.44 MB format, but you can reformat it
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to 720 KB and use it reliably after that.
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Therefore, the current recommendation is: If you format a
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diskettte to the wrong capacity, do not discard it; instead,
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reformat it correctly and use it."
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With all those feelings and recomendations on those feelings it
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makes me wonder how much experimentation was actually being done
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on a strictly scientific level. Note that the one mention of
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formatting 1.0mb disks to 1.44 MB does not say that you will get
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errors if you use them. What it does say is that if you reformat
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that wrongly formatted disk, you can reliably use it at 720 KB.
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The implication is that since there were errors with 2.0mb disks
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formatted to 720 KB "logic applies" that there will be errors if
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the reverse is done. This is not necessarly the case, and we are
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not told why, we are just told.
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FYI, here are the specifications for the 720 KB, 1.44 MB, and 360k
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5.25" disk drives as listed in the same issue on pages 43-44.
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Note the large similarity between 360k and 720 KB disks and 720 KB
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disks and 1.44 MB disks.
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720 KB and 1.44 MB Diskette Drives
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720 KB 1.44 MB 360 KB (5.25")
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Access time:
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Track-to-track 6 ms 6 ms 6 ms
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Head settle time 15 ms 15 ms 15 ms
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Motor start time 500 ms 500 ms 750 ms^
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Disk rotational speed: 300 rpm 300 rpm 300 rpm
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Maximum Latency 200 ms 200 ms 200 ms
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Formatted Characteristics: 720 KB 1.44 MB^ 360 KB^
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Tracks (actual) 80 80 40 ^
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Tracks per inch 135 tpi 135 tpi 48 ^
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Sectors per track 9 18 ^ 9
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Bytes per sector 512 512 512
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Bytes per track 4608 9216 ^ 4608
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Data heads 2 2 2
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Sector interleave factor 1:1 1:1 1:1
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Sector skew factor 0 0 0
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Sectors per cluster 2 1 ^ 2
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Transfer rate 250,000 500,000^ 250,000
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(bits per second)
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(All ^'ed numbers are numbers that are different from the 720 KB
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format.)
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"...if they think you're technical, go crude. ....
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These days, though, you have to be pretty technical before
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you can even aspire to crudeness."
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--From William Gibson's short story
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Johnny Mnemonic
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