An Introduction to PCMCIA and PC Card Technology

The Personal Computer Memory Card International Association (PCMCIA) is a standards body and trade association that consists of more than 300 member companies including manufactures of semiconductors, connectors, peripherals and systems, as well as BIOS and software developers and related industries. PCMCIA has developed standards for the personal computer cards (PC Cards). A PC Card is a small form-factor adapter for your personal computer, personal communicator or other electronic device. PC Cards are about the size and shape of a credit card.

With the proliferation of the notebook and hand-held computer system, the search for smaller, lighter, and more portable tools for information processing is generating innovative developments in many aspects of the portable computer market. These innovations include display, memory, power management, and overall computer design and size. PC Cards are a key technology for adding memory, storage, and I/O capabilities to portable systems.

PCMCIA standards describe the physical requirements, electrical specifications, and software architecture for PC Cards. The PCMCIA Specifications define three physical sizes of cards: Type I, Type II, and Type III. All three types use the same 68 pin edge connector for attachment to the computer, and differ only in thickness. The thickness for Type I, Type II, and Type III are 3.3, 5.0, 10.5 millimeters respectively.

A Type I PC Card is typically used for various types of memory enhancements, including RAM, FLASH memory, one-time programmable (OTP) memory, and electronically erasable programmable memory (EEPROM). A Type II PC Card is typically used for memory enhancements and/or for I/O features such as modem, LANs and host communications. A Type III PC Card is twice the thickness of the Type II and is typically used for memory enhancements and/or for I/O features that require a larger size, such as rotating mass storage devices and radio communication devices. Since Type I, Type II, and Type III Cards all use the same interface, the size of the card chosen for the application is dependent on the miniaturization of the technology to be implemented.

These PC Cards can be used with laptops, notebooks, palmtops, tablets, and other portable computer systems. PC Cards are convenient alternatives to pocket adapters and docking stations. PC Cards can be used with any personal portable computer system equipped with a PCMCIA slot.

The key element of the PCMCIA software architecture are Socket Services and Card Services. Socket Services is a BIOS level software interface that provides a way to access the PCMCIA sockets (slots) of a computer. Socket Services identify how many sockets are in your computer system and detects the insertion or removal of a PC Card while the system is powered on. Socket Services is part of the PCMCIA Specification and interfaces with Card Services.

Card Services is a software management interface that allows the allocation of system resources (such as memory and interrupts) automatically, once the Socket Services detects the PC Card has been added. Card Services also releases these resources when the PC Card has been removed. Furthermore, Card Services provides you with an interface to high level software to load any needed hardware drivers. Card Service is also part of the PCMCIA Specification.

The combination of PC Card hardware, Card Services software and Socket Services software provides a "plug-and-play" capability in the portable computing environment.

12/1/95 Synchrotech's Tech Support Department

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