The external hard disk have characteristics that normal hard disk do not possess.
1. Capacity
External hard disk can provide a large storage capacity, is a more cost-effective mobile storage products. In the current the price of large-capacity “flash drives” can not be accepted by users, while the external hard disk could provide the larger storage capacity and good portability within an acceptable price to the user. Currently the market could offer mobile hard drives which capacity is 80GB, 120GB, 160GB and so on up to 1TB, to a certain extent to meet the needs of users.
  External hard disk capacity of the units is MB (megabytes) GB (gigabit) TB (1TB = 1024GB), current the most of the 1.5-inch external hard disk provide 10GB, 20GB, 40GB, 60GB, 80GB, the capacity of 2.5-inch is 120GB, 160GB, 200GB, 250GB, 320GB, 1024GB (1TB), 3.5-inch HDD enclosure 500GB, 640GB, 750GB, 1TB of high-capacity, in addition to desktop-like external hard disk capacity even up to 2TB, 4TB of storage capacity. As technology advances, mobile hard drive will be increasing capacity, the volume getting smaller and smaller!
2. Size
external hard disk case is divided into two kinds: 2.5-inch and 3.5 inch. 2.5-inch external hard disk box using laptop computer hard drives, which is small and light, easy to carry, generally do not have external power supply.
3.5-inch hard drive case using desktop computer hard drives, larger, portability, relatively poor. usually comes with an external power supply and cooling fans.
3. Speed
Most of mobile hard drive use USB, IEEE1394 interface,which can provide higher data transmission speed. However, the external hard disk data transfer speed a certain extent is also limited by the interface speed, particularly in the products of USB1.1 interface specification, when transmit a larger amount of data, it will test the user’s patience. USB2.0 and IEEE1394 interface are relatively much better.
4. Easy
The current PC is equipped with the basic USB functions, the motherboard can usually provide 2 to 8 USB ports, some monitors also offer USB adapter, USB interface has become an essential interface to personal computers. USB devices are not need to install the driver in most versions of WINDOWS operating systems, with true “plug and play” features, and flexible and convenient to use. But large-capacity hard drive of 160G above due to high speed switch 7200 (the most laptop below 5400 turn). It requires an external power supply (USB power supply shortage). In a certain extent, limited the hard drive Portability!
5. Reliability
Data security has always been the issue that mobile storage users are most concerned about, it’s also an important measure of products for good or bad. External hard disk win the favor of many users with its high speed, large capacity, lightweight and convenient advantages. Such hard drives have a similar structure with notebook hard drive: multi-use silica disc. This material is more sturdy and durable than aluminum, magnetic discs, and has a greater storage capacity and better reliability, improved data integrity. Si-O is used as the material, effectively reduced the number of irregular disk which may affect the data reliability and integrity, higher hardness make USB hard disk with an high reliability.
