4 ms·

This is due to platter geometry... the "start" of the logical volume is at the outer edge of the platters, and the end is at the inner edge. If you divide the

by tomxor 5y ago

This is due to platter geometry... the "start" of the logical volume is at the outer edge of the platters, and the end is at the inner edge. If you divide the platter into concentric circles of equal width, you will notice there is more area available on the outer circles... for this reason the number of sectors per track are greater the further the track is from the centre of the platter. Yet the head will pass over the entire track in the same amount of time... i.e more data in the same time. It makes sense that the logical volume would be arranged from the outer edge to take advantage of the speed as soon as possible.

trhway 5y ago
> for this reason the number of sectors per track are greater the further the track is from the centre of the platter. Yet the head will pass over the entire track in the same amount of time... an additional consequence is that for the same amount of data it takes lesser number of tracks thus making for faster/shorter seeks inside that data.
fomine3 5y ago
> the "start" of the logical volume is at the outer edge of the platters, Is this a something like natural theory, or de facto standard? Maybe the start can be most inner edge on HDD in another planet?
- tomxor 5y ago
  It's pretty universal, as inevitable as pythagoras theorem, even on an alien planet where everything else arbitrary and historical about the technology is different: the geometry dictates this optimisation will eventually be made (zone-bit-recording) [0]. Once the optimisation is made, it's also inevitable that logical layout will start from the outer cyclinder to provide the best sequential performance at the beginning of it's use. Older HDDs did not make this optimization, they had a constant number of sectors per cylinder (track), and they also didn't come with HDD controllers, or came with more minimal controllers, and much like old floppy drives they exposed a lot of the physical layout and properties to the host system. This is why the CHS format is a historical part of OS and partitioning, modern HDDs only expose LBA. Anyway, my point is that with the older drives that lacked ZBR there is no obvious "natural law" dictating that you shouldn't create a logical layout from the inner edge - and since they exposed CHS to the OS I wonder if it was possible to chose the layout direction. [0] https://en.wikipedia.org/wiki/Zone_bit_recording https://en.wikipedia.org/wiki/Zone_bit_recording [edit] I'm trying way too hard to entertain your idea, but now I thought it I gotta write it: the one way that ZBR could exist at the same time as it making sense to start the logical volume at the inner track (or more correctly making no difference), is if the angular velocity was not constant... modern HDDs have a constant angular velocity (constant RPM), and assuming the head's maximum read capability is the linear speed at the outer cylinder, then in theory the drive could spin faster when the head is closer to the center to provide the same linear speed, at which point the sequential performance is almost constant (cylinders sector density is segmented as the area passes a threshold, so there will be a subtle periodic difference). This is how CDs work (ignoring the fact that they are a spiral), they have a constant linear speed rather than a constant angular speed and they start from the center, so the motor has to continuously change RPM to maintain it. I suspect the reason this is not used is that HDDs spin much faster than CDs, and rather than single spiral track there are cylinders that the head has to move between, the head can move between cylinders much faster than the drive motor can accurately make the subtle changes required to achieve a constant linear speed. The end result is probably very poor seek performance (i.e the seek performance would be limited by the motor rather than the head - which is very fast)... I don't know much about CDs but I suspect they also have poor seek performance, but by choice - that may have more to do with being one giant spiral track rather than motor performance.
  - fomine3 5y ago
    Thanks. Looks reasonable.

by tomxor 5y ago

trhway 5y ago

> for this reason the number of sectors per track are greater the further the track is from the centre of the platter. Yet the head will pass over the entire track in the same amount of time... an additional consequence is that for the same amount of data it takes lesser number of tracks thus making for faster/shorter seeks inside that data.

fomine3 5y ago

> the "start" of the logical volume is at the outer edge of the platters, Is this a something like natural theory, or de facto standard? Maybe the start can be most inner edge on HDD in another planet?

tomxor 5y ago
It's pretty universal, as inevitable as pythagoras theorem, even on an alien planet where everything else arbitrary and historical about the technology is different: the geometry dictates this optimisation will eventually be made (zone-bit-recording) [0]. Once the optimisation is made, it's also inevitable that logical layout will start from the outer cyclinder to provide the best sequential performance at the beginning of it's use. Older HDDs did not make this optimization, they had a constant number of sectors per cylinder (track), and they also didn't come with HDD controllers, or came with more minimal controllers, and much like old floppy drives they exposed a lot of the physical layout and properties to the host system. This is why the CHS format is a historical part of OS and partitioning, modern HDDs only expose LBA. Anyway, my point is that with the older drives that lacked ZBR there is no obvious "natural law" dictating that you shouldn't create a logical layout from the inner edge - and since they exposed CHS to the OS I wonder if it was possible to chose the layout direction. [0] https://en.wikipedia.org/wiki/Zone_bit_recording https://en.wikipedia.org/wiki/Zone_bit_recording [edit] I'm trying way too hard to entertain your idea, but now I thought it I gotta write it: the one way that ZBR could exist at the same time as it making sense to start the logical volume at the inner track (or more correctly making no difference), is if the angular velocity was not constant... modern HDDs have a constant angular velocity (constant RPM), and assuming the head's maximum read capability is the linear speed at the outer cylinder, then in theory the drive could spin faster when the head is closer to the center to provide the same linear speed, at which point the sequential performance is almost constant (cylinders sector density is segmented as the area passes a threshold, so there will be a subtle periodic difference). This is how CDs work (ignoring the fact that they are a spiral), they have a constant linear speed rather than a constant angular speed and they start from the center, so the motor has to continuously change RPM to maintain it. I suspect the reason this is not used is that HDDs spin much faster than CDs, and rather than single spiral track there are cylinders that the head has to move between, the head can move between cylinders much faster than the drive motor can accurately make the subtle changes required to achieve a constant linear speed. The end result is probably very poor seek performance (i.e the seek performance would be limited by the motor rather than the head - which is very fast)... I don't know much about CDs but I suspect they also have poor seek performance, but by choice - that may have more to do with being one giant spiral track rather than motor performance.
- fomine3 5y ago
  Thanks. Looks reasonable.