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I guess I've always assumed that HDs wrote with just a single head: moving to a specific cylinder, using a specific head, and then writing the appropriate secto

I guess I've always assumed that HDs wrote with just a single head: moving to a specific cylinder, using a specific head, and then writing the appropriate sector (CHS). But, I guess it would theoretically no different to write the stripe across all the heads in that cylinder, though for efficiency maybe the sector size would have to expand by NR_HEADS times? I guess this goes back to various diagrams I've seen over the years. Anyone able to enlighten us?

MBCook 2y ago
I guess I always assumed all the heads were independent data streams, they were just forced to move physically in parallel. You’re right that reading or writing the data in parallel across multiple platters might make more sense since the heads are always locked together anyway. I have no idea how it actually works. That had never occurred to me.
wtallis 2y ago
Hard drive tracks are really narrow. When you have one head aligned with the track on one platter, the rest of the heads on other platters will only be close to the corresponding tracks on those platters, not fully aligned. Now that hard drives are using multi-stage actuators (arms with elbows and wrists), it's theoretically possible to align multiple heads to allow writes to be striped across multiple cylinders. But I suspect those advances have instead been used to enable even tighter track spacing (and overlapping, for SMR drives) because SSDs have forced hard drive manufacturers to prioritize density over performance.
- MBCook 2y ago
  Are tracks physical things in modern disks? I’ve long assumed we got to the point where the surface of the drive was uniform recording material, “tracks” were just the parallel bands the disk made by recording data. There’s difference in the platter material between two tracks, just the gap the heads leave to avoid interference. Conceptually like audio cassette tape: it’s all magnetic, but the audio is stored in separate tracks. Is that wrong? Is there some physical coating or gap in the recording media between tracks? If that’s not wrong, wouldn’t always reading/writing the same track across multiple heads force them to stay in alignment?

MBCook 2y ago

I guess I always assumed all the heads were independent data streams, they were just forced to move physically in parallel. You’re right that reading or writing the data in parallel across multiple platters might make more sense since the heads are always locked together anyway. I have no idea how it actually works. That had never occurred to me.

wtallis 2y ago

Hard drive tracks are really narrow. When you have one head aligned with the track on one platter, the rest of the heads on other platters will only be close to the corresponding tracks on those platters, not fully aligned. Now that hard drives are using multi-stage actuators (arms with elbows and wrists), it's theoretically possible to align multiple heads to allow writes to be striped across multiple cylinders. But I suspect those advances have instead been used to enable even tighter track spacing (and overlapping, for SMR drives) because SSDs have forced hard drive manufacturers to prioritize density over performance.

MBCook 2y ago
Are tracks physical things in modern disks? I’ve long assumed we got to the point where the surface of the drive was uniform recording material, “tracks” were just the parallel bands the disk made by recording data. There’s difference in the platter material between two tracks, just the gap the heads leave to avoid interference. Conceptually like audio cassette tape: it’s all magnetic, but the audio is stored in separate tracks. Is that wrong? Is there some physical coating or gap in the recording media between tracks? If that’s not wrong, wouldn’t always reading/writing the same track across multiple heads force them to stay in alignment?