Can we write the data as a single track, that way they could spin very slowly, like a vinly record.
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The time between when a program decides it wants a block of data until it gets that block needs to be as short as possible. A big chunk of that time is waiting for the disk to rotate around until the block passes under the reading head of the drive. Sometimes you’ll be lucky and the block is right there as the drive is ready for it and other times you have to wait almost a whole rotation. On average, you have to wait half a turn^(*). This time is called the “rotational latency”.
A fast 7200 RPM drive has to wait, on average, half of one 7200th of a minute, or 4.2 ms (thousandths of a second). Slower 5400 RPM drives average 5.6 ms. These numbers are roughly a third of the total time taken to access a block of data from the disk so keeping them down is an important part of computer performance.
You might think that accessing a block every 13 ms is very fast but it’s fewer than 80 blocks per second, glacially slow in computer terms. Computers try to keep files arranged with their blocks all together so they can be read in order, without having to wait for the disk to rotate around. But with many programs running at once accessing many different files, accessing blocks essentially in random order from all over a disk is very common.
* Actually drives with smart queuing can do better. On a busy computer there will often be a long stream of requests coming in for blocks from all over the disk. Drives that support “tagged command queuing” are sent the whole list and can rearrange the order in which the blocks are retrieved, potentially allowing them to plan a tour of the disk that avoids so much waiting.
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