4 ms·

This involves simply exposing how the spinning rust drive works internally to software. On most magnetic drives there is no inherent relationship between the s

• londons_explore 7y ago
  > most magnetic drives there is no inherent relationship between the sector number and its physical location on the track This is false. Sectors are approximately in block order. You can write a predictor which can predict the latency to read a block based on the last block read using that information. You can also take the lid off a drive and watch it with a high speed camera to see where each bit of data gets stored.
  • prirun 7y ago
    On Prime minicomputers back in the 80's, there was a disk controller order to format a track. That's what broke it into sectors and put sector ID fields into each sector, in whatever way the disk controller wanted. A read was in 3 parts parts: first do a seek over the right cylinder, then select a head, then read a sector. That least part read everything spinning by until it saw a sector with the correct sector ID. Sectors were not in block order because if you read sector 1 then tried to read sector 2, it would have already spun past the head, meaning sequential sector reads would require a complete revolution of the disk. So instead, sectors were interleaved with a skip. There were 9 sectors on a track, so the sector IDs might be written as: 0 3 6 1 4 7 2 5 8. You could read 3 sectors per disk revolution instead of 1.
  • dfox 7y ago
    There usually is some relationship, but does not have to be.