How does a multi-platter hard drive address itself?

[aka1nas]

I was just curious if it addresses the platters one-by-one or if it stripes data across all the platters at once? Wouldn't the latter give better performance?

 

[Mark R]

Striping is a close approximation. The drive fills one cylinder on one side of one platter, then the equivalent cylinder on the next side, and so on. Then it moves onto the next cylinder.

Attempting simultaneously to read from more than one side, needs alignement so precise, that the thermal expansion of the moving parts as the drive warms up would stop it functioning completely.

 

[SCSIRAID]

Addressing internal to the drive is basically cylinder, head and sector. The cylinder address denotes the position of the actuator. The head value indicates which disk surface is read from (ie which head is selected) and the sector indicates which data unit (sector) is addressed. Drives only use one head at a time for data IO. The smallest unit you can directly read/write (in PC land anyway) is one sector.