Three types of PC Cards. (Personal Computer Memory Card International Association) (Compute's Getting Started with PCMCIA)
by Richard O. Mann
As technology advances, the PCMCIA standards advance. In its three-year life, the Personal Computer Memory Card International Association has approved two major releases of the standard, referred to as PCMCIA Release 1 and Release 2, specifying Type I and II cards. Most of the specs for Type III are set, but they haven't been formally ratified by the association.
You'll need to understand the differences. Each type of card (and its matching slot) is a different thickness, although all three types have the same length, width, and pin connectors. You can't stuff a Type Ill card into a Type I slot.
Type I Cards
The original PCMCIA Release 1 specifications called for a 3.3-millimeter thick card with a 68-pin connector. The standard described the card's physical requirements, electrical specifications, and software architecture.
Type I cards typically are used for memory-enhancing products. Simple RAM cards add working memory to the computer. Flash RAM cards provide memory that retains its data even when powered off, making it a super-fast hard disk substitute. ROM, or read-only memory cards, provide programs and data that can't be changed. An example is the Lotus 1-2-3 card for the Poquet computer. The entire program is on the card, but the user can't change it in any way. All writing of files must be done in the computer's other memory and storage devices.
Release 2 of the PCMCIA standards defined Type II cards, as listed below, but also refined the standards for Type I cards. Release 2 implemented significant upgrades to the standards, including Socket Services and Card Services. These two improvements let the computer sense the presence and nature of PC Cards in its sockets. Release 2 also brought the XIP (Execute in Place) standard, under which PC Cards can run as part of the computer's memory. Under XIP, a program on a PC Card runs in the card without first copying its information into standard computer memory.
Type I cards created under either standard are externally identical,but computers built with Type I slots under Release 1 can't access all the features of cards designed under Release 2.
Type II Cards
A Type II card is physically thicker than a Type I card. At 5.0 millimeters (mm), there's room for electronic devices that are too thick for a Type I card. The entire card, however, isn't 5 mm thick; the sides and pin connector area remain at 3.3 mm, so a Type II socket's guide rails and connectors will accommodate a Type I card. Any Type I card will plug into a Type II socket and work just as it would in a Type I socket. (The association plans to maintain backward compatibility: Any PC card will work in any subsequent type of slot.)
Type II cards include a number of input/output (I/O) devices, such as fax modems and Local Area Network (LAN) adapters.
Type III Cards
The Type III cards are even thicker, more than doubling to 10.5 millimeters, but retaining the 3.3 mm guide rails and connectors. These thicker cards allow all sorts of complex devices, including-amazingly enough--tiny hard disks and radio communications devices.
The current generation of PC Card hard disks use 1.8-inch spinning platters, but 1.3-inch hard disks are being developed. You can pull these lilliputian hard disks from their slots and use them in any other computer's Type Ill slot.
Radio devices make wireless and cellular communications possible--imagine being hooked into your network or making phone calls through your computer completely without external wires.
Since Type III isn't yet fully implemented and approved, most of these cards are still under development, but the standard will be issued soon and a flood of these cards will follow quickly.