Mass Storage Basics - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 7

Figure 1-3: USB flash drives provide convenient storage that PCs and other
USB hosts can access.
Selecting a Media Type
The storage media is the physical entity that holds a device's data. In embed-
ded systems, a storage device's media is typically separate from the system's
program memory, which stores the code executed by the system's CPU.
Over time, various storage technologies and form factors have come and
gone in popularity. Currently popular technologies include hard drives,
CD/DVD drives, flash-memory cards, and USB flash drives (Figure 1-3).
Other names for a USB flash drive (UFD) include USB key, pen drive,
ThumbDrive ® , DiskOnKey ® , and JumpDrive ® .
The different media types vary in the hardware and circuits required to
access the media, the ability to erase and rewrite, methods of write protec-
tion, whether the media is removable from its drive, and interface options
for external CPUs.
For many devices, flash memory is a good choice for storage media.
Flash-memory cards are physically small, can store moderate amounts of