53.hard disk internal structure

HDD (Hard Disk Drive) is the most common device for data storage. It consists of platters (or simply disks), a read/write head and actuator. There are two main connection ports you can find in HDD: IDE (Integrated Drive Electronics) and SATA (Serial Advanced Technology Attachment). IDE ports are very rare and can only be found on computers assembled before 2005. The good thing about HDD is that it can store a large amount of data and storage of 1 GB is rather cheap. Different HDDs have different capacities (the amount of GB it can store) and speeds of disk rotation (rpm or revolutions per minute). You are the one that has to decide how much space you need, but usually 320-512 GB is enough. People who store a lot of music and video files might need 750GB or more.
Most HDDs have a speed of 5400 or 7200 rpm. While 5400 is sufficient, I recommend choosing one with 7200 rpm when possible, because higher rpm translates into faster data access.
You have to remember that an HDD can be easily damaged by physical shock, because a read/write head can scratch the platter just by touching it. Considering the fact that the Hard Disk Drive rotates its platters very fast, if a read/write head touches a platter it would scratch a large part of it and make this sectors unusable. In some rare cases it can even destroy the hole platter. Even if this didn’t happen, each time that the system tries to read or rewrite a broken sector it would fail. Most likely your data will be lost forever.

It is not very common to see Hard Disks broken, but it happens. To prevent this you should use your computer or laptop carefully: don’t shake, turn over or let your computer fall while running, especially while booting up or shutting down, because your machine loads large amounts of data during this time.