CompactFlash cards are small, solid-state storage devices designed for use in portable devices. Weighing less than 15 grams each and smaller than a matchbox in size, they are highly portable and yet very tough. As such, they have been extensively used in many portable devices like digital cameras, MP3 players and PDAs for data storage.
These cards are based on flash memory technology which is non-volatile. That means it does not require power to retain its data. As such, it will not lose data even if disconnected from the host device or any power source. This is completely opposite of volatile memory technologies like SDRAM and RDRAM, where the memory cells have to be periodically refreshed to retain their contents.
Currently, there are two types of CompactFlash cards - CF Type I and CF Type II. The only difference between the two types is their thickness. CF Type I cards are 3.3 mm thick while CF Type II cards are 50% thicker at 5 mm. Other than that, they both have the same dimensions and use the same mechanical and electrical interface. So, as long as the CF slot in your device is large enough, you can use both CF Type I and Type II cards in the same slot.
CF cards are solid state devices which have absolutely no moving parts. This means they are very reliable and tough. How tough? Well, they are rated for over 2,000 Gs! How's that for durability? They can also withstand huge temperature variations! With an operating temperature range of -25oC to +75oC, there will be very few places on Earth where you won't be able to use one of these cards.
In addition to reliability and ruggedness, the solid state nature of CF cards also meant that they will consume very little power. Using only a fraction (<5%) of what small hard disks of 1.8" and 2.5" form factors normally consume, you don't have to worry about decreased battery life when you are using a CF card.
Talking about power, CF cards are really flexible. They support both 3.3V and 5V power inputs so you needn't worry whether your portable device is using a 3.3V power supply (which would be too low for 5V-only devices) or a 5V power supply (which would fry any 3.3V-only device).
Okay... enough talk about CompactFlash
cards in general. Let's check out the 64MB ACE CompactFlash