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Hi - here's some technical information for your perusal.
The Personal Computer Memory Card International Association (PCMCIA) is a nonprofit standards body chartered with establishing, marketing, and maintaining standards for credit-card-sized integrated-circuit PC cards. These types of cards are now being called "PC Card" to reflect the fact that they aren't used only as memory cards.
The Benefits of PCMCIA Cards
* Small Size
* Easy, plug-in insertion.
* High performance.
* Execute-in-Place (XIP) technology.
The PCMCIA standard specifies a removable device measuring 2.126" x 3.37" (5.4 x 8.6 cm). Basically that's the size of three stacked credit cards. PCMCIA Cards have 68 pin assignments, and interface with both 8- and 1 6-bit buses. They also support physical access of up to 64 MB of memory.
PCMCIA cards give you universal expansion capability for mobile computers, and can support a variety of functions including wireline and radio-based fax and modem capabilities, mass storage, and memory extension for host machines.
PCMCIA Release 1.0, issued in September 1990, covered memory requirements for mobile computing. Release 2.0 was issued in September 1991 and specified capabilities within the standard for modem, LAN, cellular, radio frequency, and other 1/0 peripherals. Release 2.0 is backward compatible: Cards that conform to Release 1.0 will operate in card slots that conform to Release 2.0. The current PCMCIA standard Release 2.0 also corresponds to the standards of JEIDA (Japanese Electronic Industry Association/Joint Electronic Device Engineer Council) and ISO (International Standards Organization).
There are three types of PCMCIA slots, and a fourth one is coming soon. These slots are identified by the thickness of the card that fits in them. All types are backward compatible.
Type I Cards are 3.3 mm thick. They're used primarily in Personal Digital Assistants (PDAS) and handheld devices as RAM, FLASH memory, electrically erasable programmable read-only memory (EEPROM), and one-time programmable memory (OTP).
Type II Cards are 5 mm thick and are fully 1/0-capable. You can use them for memory enhancements or for 1/0 features in modems, LAN connections, and host communications.
Type III Cards measure 10.5 mm thick. They're designed primarily for removable hard drives and radio communication devices which require a larger size. They can also be used for memory enhancements.
Type IV Cards have not yet been ratified by the PCMCIA consortium. The exact size is expected to be 18 mm thick. Type IV cards will be used for large-capacity hard drives.
How Does PCMCIA Work?
The PCMCIA standard defines six fundamental hardware and software standards for the card itself - Socket/Adapter Interface, Socket Services, Card Service, Card Information Structure (CIS), and the system software.
The PCMCIA card is plugged into a host socket/adapter on the computer's motherboard or connected to its expansion bus. The socket side has the standard 68-pin interface for the card. The adapter side translates the PCMCIA interface signals to match the computer's bus standards.
Socket Services is the software interface between the card in the socket and the adapter to the computer's bus. The standard Socket Services interface is what permits the use of any PCMCIA card on any PC equipped with a socket/adapter.
The programming interface for PCMCIA is called Card Services. It sends the signals to link Socket Services to the PC's operating system and hardware. Card Services can be implemented either as a driver, or in the operating system, as is IBM DOS 6.0.
Card Information Structure (CIS) contains information about how the card functions, its size, its electrical requirements, and so on. On card insertion, the card passes this identifying information to the host system.
The system software reads the CIS data on insertion, installs the appropriate drivers, notifies relevant system resources, and initializes the card to make it available for use by the host.
API (Application Program Interface)-
A PCMCIA-aware device driver that is provided to higher-level software than the Card Services layer. (See How Does PCMCIA Work?)
EXCA (Exchangeable Card Architecture)An extension to the PCMCIA specification, added by to ensure PCMCIA cards' interoperability on host systems using Intel CPUs.
Hot-Swapping-A hardware and software Protocol defined by PCMCIA where by PC cards can be removed and inserted into sockets without powering-down or rebooting the PC.
MTD (Media Technology Drivers)-MTDs provide an effective method for making upper software layers independent of card technology. In the future, almost every PCMCIA card will have MTDs associated with it. The MTDs will contain information such as programming algorithms for various devices on the card.
XIP (Execute in Place)-A technique by which software placed on a PCMCIA-compatible ROM card can be executed directly from the card itself instead of being loaded into RAM first.