- What's Flash Memory?
- NOR/NAND Flash Memory
- Memory cards: Form defines function
- What is CompactFlash?
- What is Microdrive?
- What is Memory Stick?
- What is SD/MMC/RS-MMC/MMC Micro/miniSD/MicroSD?
- What is Smart Media?
- What is XD-Picture card?
- Flash Drives with everything
- What are USB keys?
- What are ExpressCards?
What is CompactFlash?
CompactFlash is one of the oldest memory card formats still in current use, and its survival can be directly linked to the fact that it has been embraced by the professionals, especially for use in professional level digital cameras. CompactFlash cards are easily identified as they are physically larger than the other formats. There are two standards in the CompactFlash world, appropriately titled CompactFlash Type I and CompactFlash Type II. Both use casings that are 43mm wide and 36mm deep, but CompactFlash Type II cards are considerably thicker than their Type I counterparts -- 5mm to 3.3mm respectively. The size difference also means that Type I slots can't accommodate Type II cards, although Type II slots can take Type I cards. Typically speaking, Type I cards use flash-based memory, while the majority of Type II CompactFlash devices incorporate Microdrive-like miniature hard drives (see "Microdrives" below).
The size of CompactFlash may seem like a drawback for portable devices, but as a design, CompactFlash has certain marked advantages. For a start, the CompactFlash standard is electrically identical to the PCMCIA standard, meaning that with the use of an adapter CompactFlash cards can be directly plugged into notebook PCs. The larger size of CompactFlash slots in devices has allowed wily device manufacturers to make adapters for other common storage media that fit within the slot -- so it's feasible to use an SD card in a CompactFlash slot, something that's physically impossible in reverse.
CompactFlash write speeds vary depending on the standard used; the CompactFlash Specification 2.0 supports data rates of up to 16MBps, while the 3.0 specification supports rates of up to 66MBps. Electrically, CompactFlash supports voltages of 3.3V and 5V, and any compliant card should support both voltages. CompactFlash cards are also available in packaging that supports operation in extreme temperature variants, from -40 C to +85 C.
The larger package size, market position in the professional space and electrical PCMCIA compatibility means that CompactFlash is also used for a variety of other applications such as miniature network cards.
What is Microdrive?
Microdrives are CompactFlash Type II sized miniature portable hard drives, initially developed by IBM in 1999. Development is now handled by Hitachi after the company purchased IBM's hard disk division in 2002. Unlike flash-memory-based devices, Microdrives use actual miniaturised hard drives with read heads and moving parts. This makes them more susceptible to drop shock and associated problems, although they are remarkably resilient devices in actual use.
Where Microdrives score highly is in the capacity they're able to offer -- Hitachi recently announced 20GB Microdrives -- at a much more compelling price point than solid-state alternatives. Because they have moving parts to operate, Microdrives do draw more power than other solid-state CompactFlash devices, and some Compact Flash-compatible devices may not be able to utilise Microdrives, or may suffer much lower battery life when they do. Again it's the professional world that has embraced Microdrives, especially in the professional camera world, where multi-gigabyte Microdrives were the norm while competing formats were topping out at the 512MB limit.