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.
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.
Table 1-4: CompactFlash cards are available in several formats.
CompactFlash and CF+ cards with storage media are accessed much like other ATA hard drives. A series of registers store status and control information and data being transferred. The CompactFlash specification defines a CF-ATA command set for communicating with cards.
The CF+ and CompactFlash specification is available at no charge. Use of the CompactFlash logo and trademarks on products requires membership in the CompactFlash association at $2500 per year.