Many of the first computers did not have a storage device where to save the information and the applications, in this way all the information was in the RAM all the time, and this information was deleted every time the pc was turn off. (We must remember that the RAM, is a kind of memory volatile, also known as work memory because is available to use when the pc is turn on)

But in the common life we need to store many information, for example to support complex tasks, to record a lot of events or to save all the users that works on a company, it's not very useful have to start again every day.

The hard drive is a good technology evolution, to support the information storage. Today almost all the computers have at least one. With this device we can save there the operative system, applications and all the user information as music, documents, videos, movies, images, etc.

Making a review of hard drive we can found that today have some variants:

Common hard drive: Is a data storage device where we can read, modify and write digital information, this information is recorded on some disks coated with magnetic material, the disks are rapidly rotating, and with some magnetic heads, the information is retrieved, modified or written. This kind of disks can be easily damaged and must be handled with care. An actual hard drive can have from 40GB to 4 or more TB of space, and it's commercial two diferents sizes 3.5 inches for desktop computers and 2.5 inches for laptops and other little devices.

Solid State drive:

Is a kind of hard drive that only use integrated circuits to storage information and not magnetic disks as the common disks. This new technology bring hard drives with more speed, more effiency, low energy consumption, etc. This hard drives don't have any mobile part, and use the same SATA interface as the common hard drive to comunicate with the computer. Today this kind of hard drives are very expensives and have less capacity as the common hard drives, but sure if you are planning get more speed on your computer, you can consider replace your main hd for a good SSD.

Hybrid hard drive:

It's a mix between a common hard drive and a SSD in one device that bring you some adventages of the two worlds, for example you can get more capacity than a SSD and at the same time with a lower price.