Disk capacity
Most external hard drives can contain from 2 GB to 4 TB of information, there are also models with a capacity of 8 TB. To determine how much memory you need, decide what you plan to store on the disk. If you are looking for a medium for recording large amount of video, consider purchasing disk capacity of 1 TB. If you need media to store emails and text documents, disks, compact size, accommodating a few gigabytes.
Data transfer rate
The speed with which information will be recorded on the hard disk is also very important. If you plan to use the drive for storing backup data written 1-2 times a week, you can use any external disk drives. If the media you need for everyday use, including for recording large files, it is best to choose a drive with a higher write speed.
USB 2.0 interface remains common, its speed is quite high, however, for writing large files, it is preferable to use the USB 3.0, the speed of which is much higher. The eSATA interface is more complete, but disks with that interface are expensive. Selecting the connection interface, note the presence on your computer the appropriate connectors.
Portability
An important factor in the selection of the external hard drive is a method of its use and storage. If you are looking for an additional, external device for storing data, which is not planned to carry from place to place, the ideal option for you will be CDs large in size, but containing a significant amount of information. They usually need their own power supply from the mains. These disks are slightly cheaper portable devices of comparable capacity.
Portable hard are compact, have high strength, protecting them from drops, and don't need separate power adapters. They are most often used for frequent transfers of information from one device to another, as well as for work, when all necessary information is always available at hand.
Security
Storing on an external hard drive of confidential information concerning personal data is quite dangerous, especially if this disk is often connected to various devices. If you use it for such purposes, be sure to verify availability of hardware-based encryption of data. This encryption is much safer software.