Flash memory is by definition non volatile, i.e. if you turn the power off, the data doesn't disappear, unlike DRAM. EEPROM is also non volatile, but you have to erase it first using ultraviolet light, then reprogram it. With flash, there is a control sequence to reprogram it on the fly that could be done by a microprocessor. A flash card (i.e. Compact Flash) contains a bunch of flash chips, plus some controller, and could be plugged into a PCMCIA interface for instance on your PC or digital camera. Note that the PCMCIA interface allows hot swap, meaning that you can unplug one flash card and plug in another flash card without having to turn off power.
A flash drive is also a card containing a bunch of flash chips but it contains some controller that emulates a hard disk, therefore for the PC, it looks like you have a hard disk drive plugged in (drive D for instance). You plug the flash drive on the PCMCIA interface or IDE interface of your PC. Flash drive is also hot "swappable" with PCMCIA. If you run out of storage, you just replace with a new flash drive like you do with a floppy disk or a zip disk. Flash drive is also non-volatile. It's faster than hard disk because there is no moving part, can withstand extreme temperature (hot or cold), can operate in high vibration environment. Max storage is currently 240MBytes; next year, Sandisk will release a 500MByte flash drive. Only drawback for flash drive is cost ($1700 for 500MBytes). Hope this help. |
