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"
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Replying to @whitequark @bofh453
How do you use FFT to recover data? Perhaps you mean FEC.
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Replying to @ortegaalfredo @bofh453
no, FFT. google "shingled magnetic recording", it's really wild. you do FEC *afterwards*.
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it’s literally MIMO except instead of a radio channel you have a magnetic recording channel
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and it's in like, time domain slightly more so than space domain? but yeah, MIMO is a good way to look at it
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well it’s also in space domain because shingled writes are physically in different locations on the platter
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To me it looks similar to OFDM, in which you also use FFT to modulate/demodulate overlapping channels.
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the channels in SMR aren’t orthogonal, there’s explicitly inter-channel interference, with OFDM i thought there was a requirement for subcarrier orthogonality
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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.
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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.
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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
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