Can we write the data as a single track, that way they could spin very slowly, like a vinly record.
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I’m going to go back to old hard drives to make this simple, and counting a drive with only one platter (disk), but the general idea still applies.
A hard disk is concentric rings, each divided up into sectors that hold your data. For discussion, our disk has 1,000 tracks (rings) of 64 sectors each for a total of 64,000 sectors. Each sector hold 512 bytes of data, so it can hold 32,768,000 bytes (32 MB) on one side, or double that if we read from both sides. So we have a 64 MB hard disk (that was big at one time).
Now we sandwich the disk between two read/write heads and spin it like a record, which is about one rotation every two seconds (rounding). So every two seconds we read one track. We have a thousand tracks. It’s going to take us over half an hour to read the 64 MB on that hard disk. That’s very slow.
And that’s just for reading the whole thing at one time. Think of when we just try to start reading a file. Wherever the read head happens to be now, we have to wait for the first sector of the file to come under it for it to read, which can be anywhere from zero to two seconds. Ouch.
Files are also not always nicely lined up in adjacent sectors. A file’s sectors could be all over the place. So think of a clock, and the disk is spinning in the direction the hands on a clock go. Your file uses four sectors (2 kilobytes). The first sector is at 3 o’clock, second at 1`2, third at 6, fourth at 9. So we read the first sector (at 3), then we wait a second and a half for the disk to come around to the second sector (at 12), then another second for the third (at 6), and then a half second for it to come around to the fourth (at 9). We just waited three seconds to read 2 kilobytes of data.
Now we spin it as fast as a modern hard disk at 7,200 rpm, or 120 rotations per second. We can read the whole disk in just over 8 seconds. It will take us at most 1/120th of a second for any one sector to come around under our read head. The spread out file above will take 1/80th of a second to read.
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