Hard Disks

Decomposition

• An HDD contains lots of platters. A spindle typically has 1~5 platters on it.
• Each platter has one read-write head.
• Each platter has 50~100k tracks in it
• Each track has sectors in it. Inner tracks have 500~1000 sectors while outer tracks have 1000~2000 sectors
• A block is the smallest unit of storage allocation. It is typically 4~16 kB in size.
• A cylinder \(i\) contain's the \(i^{th}\) track of each platter

Read-Write

• The read/write head needs to be above the correct sector to read from it.
• The disk arm swings to the correct position to accomplish this.
• Meanwhile the disk spins continuously. Eventually, the track head will be in the correct position.