PCMCIA, Cardbus and ExpressCards are similar technologies that are very easy to confuse with one another. In fact, many experienced computer users still get the standards confused. Let us try to shed some light on the differences between these three standards, and eliminate some of the confusion.
PCMCIA stands for Personal Computer Memory Card International Association, the organization which standardized the format. It is an interface for connecting external memory cards, modems, and other devices to a laptop as a means of expansion. It later began to be referred to as “PC Card” instead of its long acronym.
The first cards were Type I cards, which had a 16-bit interface and were 3.3 mm thick. These Type I cards were prevalent on many of the early Compaq laptop systemboards. Type II cards are somewhat thicker, at 5.5 mm, and use either a 16-bit or 32-bit interface. Common Type II devices are modems and network cards, which often have to use a dongle, as their height does not support a full-size jack. Type III cards and devices are even thicker, at 10.5 mm thick, and can support full-size connectors without dongles and even hard disk drive cards. Type II Cards were the standard size of PCMCIA Card for some time before they were replaced by CardBus.
CardBus is the successor to PCMCIA. In fact, it is the name used for cards and devices that supported the PCMCIA 5.0 or later specification. It has much in common with the PCI bus on a desktop computer, as it provides a 32-bit, 33 MHz PCI bus with a smaller form factor designed for laptops and notebooks. Most CardBus slots support earlier PCMCIA devices, but CardBus devices can not be inserted into older slots, as they are notched differently. If these newer cards are forced into the older PCMCIA slots, it can cause damage to the card slots and a relatively expensive laptop repair.
ExpressCard is the latest successor to be developed by the PCMCIA organization. It was introduced in 2003 to replace earlier form factors. There are two form factors included in the specification that are used on laptop systemboards; Expresscard/34, which is 34 mm wide, and ExpressCard/54, which is 54 mm wide. ExpressCard/54 cards can be rectangular or L-shaped, supporting either 26 pins or 68 pins. ExpressCard/54 slots are often used on HP laptop systemboards to support a remote that conveniently hides away in the slot. The ExpressCard interface allows for much more bandwidth than previous technologies, up to 2Gbit/s. This allows users to connect high-speed disk drives and other devices that need more bandwidth to operate effectively.
Understanding the progression of these three technologies will hopefully clarify their differences and applications. Currently, ExpressCard slots offer the best performance for external devices, but it will likely be replaced by a faster technology in the future as well.