PCMCIA Basics

As the demand for notebook and laptop computers began skyrocketing in the late 1980's, users realized that their expansion options were fairly limited. Mobile machines weren't designed to accept the wide array of available expansion cards that their desktop counterparts could enjoy.

In June of 1989, a non-profit trade association and standards body known as the Personal Computer Memory Card Industry Association, or simply PCMCIA, was formed in Sunnyvale, CA with the intention of establishing, marketing, and maintaining a new expansion technology designed specifically for on-the-road computing. A credit card-sized casing would be developed to house a new generation of micro expansion cards that notebook & laptop users could use to add memory, storage, or communication capabilities to their machines on the fly. Hence the PCMCIA card, which has become more commonly known as the PC Card, was born.

Card Types
  • Type I PC Cards are typically used for memory devices such as RAM, Flash, OTP, and SRAM cards.
  • Type II PC Cards are typically used for I/O devices such as data/fax modems, LANs, and mass storage devices.
  • Type III PC Cards are used for devices whose components are thicker, such as rotating mass storage devices. These Extended cards allow the addition of components that must remain outside the system for proper operation, such as antennas for wireless applications.


All three card types measure the same in length and width, and use the same 68-pin connector along the edge for connecting to a computer. The only difference between the card types is thickness, which vary as 3.3, 5.0, and 10.5 millimeters for Type I, Type II, and Type III cards respectively. Because they differ only in thickness, a thinner card can be used in a thicker slot, but a thicker card can not be used in a thinner slot.

Release Numbers

 The release number refers to the version of the PC Card Standard that a particular card or system was based on. Basically, release 1.0 supported memory only, and 2.X releases supported memory and I/O applications.

  • PCMCIA Standard Release 1.0/JEIDA 4.0 - June 1990 The first release of the standard defined the 68-pin interface and the Type I and Type II PC Card form factors -- basically the electrical and physical requirements for memory cards only. It also defined the Metaformat or Card Information Structure (CIS), which is the format in which information regarding the card's content and operating specs are stored on the card. There was no concept of input/output (I/O) cards in the first release of the PC Card Standard.
  • PCMCIA Standard, Releases 2.0, 2.01 and 2.1 - 1991-1994 The second release of the standard defined an I/O interface for the same 68-pin interface as was used for the PCMCIA memory cards in the first release of the Standard. Release 2.0 clarified the original release, added support for dual-voltage memory cards, and introduced sections dealing with environmental requirements and testing methods. Release 2.01 added the PC Card ATA specification, the Type III card type that is now followed by hard disk PCMCIA card manufacturers, and the Auto-Indexing Mass Storage (AIMS) specification, which is geared toward digital image handling & storage. It also included the initial version of the Card Services Specification, which is the software side of the PC-to-card interface. Release 2.1 further enhanced the Card and Socket Services specification, and made improvements to the Card Information Structure.
  • PC Card Standard-February 1995 The latest release of the PC Card Standard improved overall PCMCIA compatibility and added support for features such as 3.3 volt operation for power-saving notebook computers, Direct Memory Access (DMA) support for faster throughput, and 32-bit CardBus busmastering for 32-bit applications.


Compatibility

 PCMCIA’s goal is to make the technology as easy to use as possible. However, the standard can only provide guidelines. There are PCMCIA card and notebook computer manufacturers who do not follow the standard exactly, or have interpreted it in their own way, which has caused some compatibility problems; a given PCMCIA card that runs on one machine or platform is not guaranteed to run on all machines.

During the last few years, there have been three major factors that have come together to greatly improve PC Card interoperability. In the March 1995 release of the standard, the software specification for PC Cards were improved in a number of ways. Improvements to the Card Information Structure and the guidelines for its usage improved the way that hosts recognize the features and requirments for a card when inserted.

Also part of the March 1995 release was the addition of the Guidelines document, a series of recommended guidelines for developers of specific types of PC Cards, such as modems, wireless devices, ATA cards and CardBus cards.

In addition, increasing cooperation between card, host and software developers within the industry has resulted in improved interoperability. Towards this end, PCMCIA and the Plug and Play Association regularly co-sponsor Plug Fest Interoperabilty Workshops that bring together leading manufacturers from all parts of the industry.

Features of PC Card Technology
    Card Information Structure - The CIS describes the characteristics and capabilities of the card so the host system can automatically configure it. CIS is defined in the Metaformat Specification.

    CardBus - CardBus allows PC Cards and hosts to use 32-bit busmastering and to operate at speeds up to 33MHz.

    DMA - The Standard allows cards to utilize Direct Memory Access technology directly in the hardware when matched with a corresponding host system.

    eXecute In Place (XIP) - Allows operating system and application software to run directly from the PC Card, eliminating the need for large amounts of system RAM.

    Low Voltage Operation - The Standard enables 3.3 and 5 volt operation. A physical keying mechanism for 3.3 volt cards protects them from being damaged in a 5 volt slot.

    Multiple Function PC Cards - The Standard enables truly standardized multiple function PC-Cards.

    Plug and Play - PC Cards can be inserted or removed while the system is on because power and ground contact pins are the longest contacts, ensuring that disconnect signals disengage first, preserving data integrity.

    Power Management - The Standard provides a means to interface to APM (Advanced Power Management) through the Card Services Specification.

    Zoomed Video (ZV) - Zoomed Video is a connection between a PC Card and host system that allows the card to write video data directly to the VGA controller. The data is transferred with no buffering requirements because it is transferred over the ZV bus and not the system bus.