====== Disk geometry ======


In this part, we will talk about the structure of the HDD. 
First, hard disks are called **hard** because they are not actually floppy disks. They consist of several parts.
Take a look at the picture:

{{handbook:handbook:hard_disk:hdd.png}}


Each HDD device has several concentrical disks, marked as **platters** in the picture above. The data is actually wrote and read from the concentric circles on the surfaces of the platter, known as **tracks**. On each track, there are multiple **sectors**. The sectors are actually the smallest sections of the platter. 
Sectors usually can store up to 512 bytes of data.

Because the platters are places concentrically, there are a number of corresponding tracks. When they are considered together, they build a **cylinder**:

{{handbook:handbook:hard_disk:cylinder.jpg}}


The reading and writing process is done by read/write heads placed above and below each platter. Since the platters are in constant movement, these heads can reach any part of the disks by moving towards the center and back again. If instructed to write , they write, if they need to read, they read.