PCMCIA-PC Cards - The Necessary Facts

The term PCMCIA in fact refers to the Personal Computer Memory Card International Association, the governing body that oversees the development of the device. However, PCMCIA and PC Cards are used to refer to the devices themselves and the term has become interchangeable.

As laptop and Batgirl computers gained popularity and widespread use, it became necessary to develop a means to connect them with other peripherals, as is usually done with desktop computers.

PCMCIA and PC Card

Given the wide array of manufacturers, both of notebook computers and peripherals, this hardware was established to make sure that a single interface be created that was compatible with both. This led to the creation of the first PCMCIA or PC Card in 1990.

Even during its early release, the PC Cards became very popular, as for the first time, mobile users could now attach any number of needed devices, from modems, to sound cards, hard disks and network adapters to their laptops. It made the data transfer and synchronization of relevant information on desktop, laptop and network computers easy.

Specifications

There have been three classes of PCMCIA cards: type I, type II and type III.

The type I PC Cards were about 3 millimeters thick, and provided support for flash and DRAM memory cards. Type II cards are slightly thicker at 5mm, and are now the most frequently used. Type II cards provide support for more devices and work well with other memory management software.

Type II utilizes a 16 bit or (more commonly) a 32 bit interface. It has I/O support, which gives portable devices the ability to either attach to other devices, or use connectors and slots so it can interact with them, despite having no local support.

The Type III PC Card were designed to accommodate those components that Type II PC Cards could not. The primary example of this would be drive cards for hard disks.

Type IV Cards have been developed, but it has not yet been declared a standard by the PCMCIA.

PC Card Drivers

To use these cards, drivers need to be installed. These come in two forms, the Card Services and Socket Services. The former are used to oversee hot swapping and also assign the resources needed by each respective peripheral. Card Services also look over the IRQ (interrupt request) and the I/O addresses.

Socket Services, on the other hand, were built to directly interact with the PC Card controller chip and are usually located in the BIOS.

The CardBus

The CardBus refers to PCMCIA 5.0 or later. This came in the mid 1990s and have become part and parcel of laptops since then. Its specifics are virtually identical to a PCI bus with a 32 bit interface and a clock speed of 33Mhz. Like PCI devices, the CardBus allows for bus mastering, which opens the door for communication between a controller and a device without the need to pass by the central processing unit.

Most chipsets today sustain both the CardBus and PCI, even the later ones that have been developed with Wi-Fi support.

The increasing demands on laptops today require greater compatibility with an assortment of different components. For this reason it is to be expected that PCMCIA /PC Cards will continue to play a role in processing and synchronizing data between computers and peripherals.

Peter Garant is writing articles about PCMCIA cards for a site about PCMCIA.