Anatomy of hard-disk














# Anatomy of hard-disk
- **platters **and **double of heads of platters**
- since we can use upper and lower of platter
- usually **sector **is 512 bytes
- head need physical take off and landing - slow
- **Disk address = (driver, surface, track, sector)**
- Cylinder-based mapping


- Seek time : The head is moved to the target track
- latency : Rotational latency
- Transfer time: Read/write the sector
![](https://www.notion.so/image/https%3A%2F%2Fs3-us-west-2.amazonaws.com%2Fsecure.notion-static.com%2Fcee3253a-c7b1-499f-accc-489628ef3d46%2Ftemp.jpg?table=block&id=ab97e574-2861-4904-90ea-f9a11fccce0d&cache=v2)
![](https://www.notion.so/image/https%3A%2F%2Fs3-us-west-2.amazonaws.com%2Fsecure.notion-static.com%2F6578359c-9bba-4b35-80a4-ba9b4bd1ce17%2Ftemp.jpg?table=block&id=130aa835-3424-4abc-85c4-da18252e6633&cache=v2)
### Mapping algorithm or disk addressing
<details><summary>

Mapping from sector address to logical block address</summary>

(surface j, track i, sector k) = k + s * (j + i*p)
- Assuming p surfaces in the disk and s sectors per track.
</details>
