PCMCIA
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Introduction
Also known as PC Cards, PCMCIA was originally designed as a solid-state memory card format used by notebook computers. Since it's inception in 1990, this standard has evolved to become a powerful general-purpose expansion interface for a variety of devices. It is just now being phased out in favour of the newer Expresscard interface.
Form Factor
PCMCIA cards are 85.6x54mm in size, and either 3.3mm (type I), 5.0mm (type II) or 10.5mm (type III) thick. If necessary, the standard also allows the cards to extend beyond the length of the slot to accomodate components like antenae.
As the Compactflash standard is derived from PCMCIA, the thickness of each of the three types are identical to the smaller cards. See figure 1 for a comparison of the two card formats.
Variants
ATA Mode
The original transfer mode offered by the PCMCIA standard, this mode is electrically compatible with conventional PATA hard drive interfaces. This allows PCMCIA-based memory cards (or adapters) to be accessed as if they were directly attached to a hard drive controller in the computer.
16-bit Cards
The conventional 16-bit PCMCIA interface provides basic conectivity for low-bandwidth devices like modems or memory cards. Unlike the ATA mode, this interface is flexible and can operate with any type of expansion card. This bus runs at an 8MHz clock rate, providing a theoretical bandwidth of up to 16MB/s. While sufficient for many tasks, many newer technologies required higher bandwidth.
Cardbus
As higher transfer rates became necessary, version 5.0 of the PCMCIA specification added a new 32-bit transfer mode called Cardbus. In addition to the wider bus, Cardbus devices operate at a much faster 33MHz clock rate - providing a theoretical bandwidth of up to 132MB/s. This substantial increase in throughput made it practical for high-bandwidth devices (like network or WAN cards) to use the PC Card slot effectively.
It is important to note that while Cardbus slots can accept any type of card, Cardbus cards can not be used in older slots. This is generally not an issue, as Cardbus slots are available in nearly all portable computers made in the last seven years. Cardbus cards can generally be identified by a copper grounding pad directly above the socket end of the card.
Support
Nearly all modern portable computers are equipped with Cardbus-capable PCMCIA slots. While some newer machines have moved to the newer Expresscard standard, most of these also contain PCMCIA slots (the Apple Macbook Pro is one of the major exceptions).
While a number of early Kodak DSLRs used PCMCIA memory slots, these cards are too large for modern camera designs. As such, these cards are generally used only for expansion of portable computers and are not generally used for memory cards at this stage.
See Also
- Expresscard - A newer PCI-E-based expansion slot for portable computers. Intended to eventually replace PCMCIA, it is still in the early stages of adoption.
- Compactflash - A compact version of this standard for use in smaller devices such as digital cameras.
