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alt_kia's profile
Kia‏☆
Kia‏☆
Kia‏☆
@alt_kia

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Kia‏☆

@alt_kia

⁂ dysfunctional Verilog programmer ✦ shockingly nice under the circumstances ✦ patreon: https://www.patreon.com/user?u=12717330  ⁂

Joined April 2013

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    1. whitequark‏ @whitequark Oct 24

      Hey, old people of Twitter. How does a 3.5" floppy disk drive know where it should pulse the INDEX pin of the interface? On the drive I have it seems to pulse it at the same time but it doesn't seem to correlate at all with the first sector on the track.

      7 replies 5 retweets 9 likes
      Show this thread
    2. whitequark‏ @whitequark Oct 24

      Apparently there used to be an actual index hole and an optocoupler but I cracked open one floppy disk just to be *real* sure and guess what? Zero holes. So it must be doing it in some other way, and I think it's fucking up or something.

      3 replies 0 retweets 2 likes
      Show this thread
    3. whitequark‏ @whitequark Oct 24

      Why do you even *need* an INDEX pin on the interface? Doesn't it have in-band signaling and an enormous amount of sync bytes to help you locate where the data starts? Is it just to detect how fast it is rotating / when you have read the entire track?

      4 replies 1 retweet 4 likes
      Show this thread
    4. whitequark‏ @whitequark Oct 24

      Floppy disks are a decidedly baroque data storage standard but I'm enjoying these in a perverse way, I don't think I'll get another chance to be this close and personal to magnetic domains. Also everything's fucked up and horribly inefficient so that's fun too

      4 replies 0 retweets 20 likes
      Show this thread
    5. whitequark‏ @whitequark Oct 24

      modern hard drives: "let's overwrite 80% of the tracks and then use FFT to recover data, YOLO" 3.5" floppy drives: "let's just spend like 20% of the entire media on 0x4E sync bytes alone, and then use a 1b2b encoding for the rest, lol"

      5 replies 8 retweets 36 likes
      Show this thread
    6. Alfredo Ortega‏ @ortegaalfredo Oct 24
      Replying to @whitequark @bofh453

      How do you use FFT to recover data? Perhaps you mean FEC.

      1 reply 0 retweets 0 likes
    7. whitequark‏ @whitequark Oct 24
      Replying to @ortegaalfredo @bofh453

      no, FFT. google "shingled magnetic recording", it's really wild. you do FEC *afterwards*.

      1 reply 0 retweets 1 like
      Kia‏☆‏ @alt_kia Oct 24
      Replying to @whitequark @ortegaalfredo @bofh453

      it’s literally MIMO except instead of a radio channel you have a magnetic recording channel

      3:43 PM - 24 Oct 2018
      • 2 Likes
      • Peter Barfuss 𒀱 whitequark
      1 reply 0 retweets 2 likes
        1. New conversation
        2. whitequark‏ @whitequark Oct 24
          Replying to @alt_kia @ortegaalfredo @bofh453

          and it's in like, time domain slightly more so than space domain? but yeah, MIMO is a good way to look at it

          1 reply 0 retweets 0 likes
        3. Kia‏☆‏ @alt_kia Oct 24
          Replying to @whitequark @ortegaalfredo @bofh453

          well it’s also in space domain because shingled writes are physically in different locations on the platter

          1 reply 0 retweets 0 likes
        4. Alfredo Ortega‏ @ortegaalfredo Oct 24
          Replying to @alt_kia @whitequark @bofh453

          To me it looks similar to OFDM, in which you also use FFT to modulate/demodulate overlapping channels.

          1 reply 0 retweets 0 likes
        5. Kia‏☆‏ @alt_kia Oct 24
          Replying to @ortegaalfredo @whitequark @bofh453

          the channels in SMR aren’t orthogonal, there’s explicitly inter-channel interference, with OFDM i thought there was a requirement for subcarrier orthogonality

          2 replies 0 retweets 1 like
        6. ЬᏂ​au​ϮᏂ‏ @peroxycarbonate Oct 24
          Replying to @alt_kia @bofh453

          I was curious about something and thought you might know: Why did high density perpendicular hard drives not appear earlier? That was demonstrated in a commercial product in 1984, then it didn't really reappear until 2006.

          1 reply 0 retweets 0 likes
        7. ЬᏂ​au​ϮᏂ‏ @peroxycarbonate Oct 24
          Replying to @peroxycarbonate @alt_kia @bofh453

          Was it because it only really helps if you decrease head height over the platter, and manufacturing of smooth enough disks was a problem? The solutions that were found to that seem pretty obvious but maybe my perspective is skewed.

          1 reply 0 retweets 0 likes
        8. Kia‏☆‏ @alt_kia Oct 24
          Replying to @peroxycarbonate @bofh453

          am unsure, would need to look up information on requirements for read head, write head, and of media stackup and when those were developed; it’s likely that there was no need to go to perpendicular recording if areal density increase could be achieved with traditional recording

          0 replies 0 retweets 1 like
        9. End of conversation

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