· The most important factor is probably the cost. In terms of dollars per gigabyte (GB), an external hard drive is superior to flash memory. You can buy a 1 terabyte (TB) drive--1,000 gigabytes--for less than 100 dollars. Meanwhile, a 64GB flash drive will cost you about $150, and a 128GB flash drive goes for around $400. As larger sizes are introduced, the older ones will drop in price, but there will always be a substantial spike for the premium model.
· Furthermore, 512GB is the largest flash drive currently available, and flash memory has always trailed hard drives in storage capacity; do not expect this gap to close any time soon. Three-terabyte external drives are available, and you can expect this ceiling to increase about 500 GBs every six months, judging by historical trends. You can even purchase 4TB and 6TB "drives," but these enclosures actually just hold multiple 2TB drives.
· As far as transfer speeds go, both flash memory and hard drives are limited by USB 2.0's limit of 480 megabits per second, or 60 megabytes per second. However, many external hard drives also offer an external connector for "eSATA," which allows a standard hard drive to operate at its typical 150-megabyte peak rate.
If your computer does not have an eSATA connector, you can buy a peripheral card for about $25. Laptop users can buy CardBus cards for eSATA as well, for around $30.
Flash drives are small but expensive per gigabyte.
When it comes to portability, however, flash memory is king. Although it is expensive, a thumb drive can fit on a key chain or around your neck on a lanyard. Flash drives are much lighter and smaller than any external drive on the market. Plus, you do not need cables to attach them; just plug them in to a USB 2.0 port on your computer.
· Another advantage to flash drives is power requirements. Most external hard drives require an AC adapter plugged into the wall or into a power strip. A flash drive, however, draws all the power it needs from a USB port. If you lose your AC adapter, you may have to contact the manufacturer for a replacement, and if the product has been discontinued, a replacement may not be available.