How are larger HDDs made?

[EminentSun]

So i was just wondering, how do hard drive manufactures fit differing amounts of data (500gb vs 8Tb) on the same sized disk. A link to further reading would be much appreciated.

[79wjd]

By using higher density disks and or putting more disks inside the drive. 

[XenosTech]

1 minute ago, EminentSun said:

So i was just wondering, how do hard drive manufactures fit differing amounts of data (500gb vs 8Tb) on the same sized disk. A link to further reading would be much appreciated.

Platters platters and more platters

 

[mariushm]

Hard drives have several platters inside (discs) , each with two surfaces. A hard drive has between 1 an 6-8 platters but anything above 4 is kind of difficult to make reliably and typically you'll see a lot of them only on more expensive enterprise drives (and the helium based drives for example, which can afford to put platters closer together as there's no air inside to complicate things)

 

So if you want a 500 GB drive, they may use 1TB platters, so you have only one platter inside but use just one read/write head, effectively using only one side of the platter to store data.  The same drive could be made to store 1 TB by adding a read/write head for the other side and by "formatting" the platter surface to hold data. A few minutes more in the factory to format the surface and change the firmware.

 

Some companies start manufacturing platters with higher densities of data in new factories while maintaining production in older factories which already made back the money invested in them. When this happens, entry level hard drives often start using those older generation platters and newer bigger hard drives would use the newer type platters. So for example, 400-500 GB drives could have two platters inside each holding around 300 GB of information, so they use 3 surfaces out of the 4 available to store data or something like that, while new hard drives would use 750 GB - 1 TB platters  (and that's also one reason why newer hard drives have faster speeds, in one rotation the head reads more bits due to information being more densely packed on the surface) .

 

Still it's a balancing trick, because the more platters inside the harder it is to balance them and calibrate the hard drive and extra read/write heads cost money, so the moment a new factory produces those new platters in volume with minimal rejects, the old platters are not cheap enough to be worth it.