External hard disk drives are externally connected through a cable to a compatible computer. Since the advent of Internet more back up files for information are needed making external hard drives popular among users of all platforms. Presently, the market for external hard disks is aimed towards portability and increase in memory.
External hard disks are inexpensive with larger capacities. But they are far more fragile than pen drives and are less resistant to shock, have limitations on use at high altitude, and are vulnerable to electromagnetic fields. They are larger and heavier and suffer from file fragmentation which can significantly reduce performance.
Pen drives store data in an easier and simpler format. They are small, handy, portable and easy-to-use storage devices that can store large amounts of data. You can easily use it anywhere. With most computers and laptops having USB ports all you need is to plug in and transfer the files from pen drive to the PC.
Most OS like Windows, Mac OS X, Unix and Linux support pen drives and connectivity will never be an issue. Although pen drives do not have that much storage capacity as hard disk they are small, durable, easy-to-use and convenient to maintain. They now have storage capacity of more than 65 GB. Storage of data using a pen drive is safer and you will not lose data due to read or write errors. They can handle factors like shock, pressure, moisture and heat better than other storage devices.
For a short comparison between a pen drive and hard disk, you can check this link,
Comparison with Hard Disks
