Mass Storage Basics - USB Mass Storage: Designing and Programming Devices and Embedded Hosts - page 23

ory, registers, and an intelligent controller. CompactFlash was introduced by
SanDisk Corporation. These cards are a solution if you need to store a lot of
data in a small package or need very fast transfers.
Packages
Table 1-3 compares the two CompactFlash variants. Both are 1.7 in. wide
and 1.4 in. or greater in length. A Type II CompactFlash card is thick
enough (about 0.2 in.) to hold a tiny hard drive. A CF+ TM card is any card
that has the CompactFlash form factor and contains storage media other
than flash memory or performs I/O functions other than storage.
Interfacing
CompactFlash cards can use an 8- or 16-bit parallel data bus. Storage
devices can use either of two modes. PCMCIA mode is based on the PC
Card (PCMCIA) interface and uses an 11-bit address bus. True IDE Mode
is based on the ATA-4 specification, is compatible with the IDE disk drive
interface, and uses a 3-bit address bus to select registers.
A CompactFlash card can draw up to 75 mA at 3.3V or 100 mA at 5V. A
CF+ card can use either of two power levels. The limits for Power Level 0 are
the same as for CompactFlash, while Power Level 1 allows drawing up to
500mA at 3.3V or 5V. All currents specified are average RMS currents.
Figure 1-8: A CompactFlash card is another option for flash-memory storage.