Name
PCMCIA originally stood for Peripheral Component MicroChannel Interconnect Architecture. This awkward initialism was jokingly expanded as "People Can't Memorize Computer Industry Acronyms" or "Personal Computer Manufacturers Can't Invent Acronyms". It was then retronymmed to name the standards organization, the Personal Computer Memory Card International Association. Difficulty with the acronym led to the simpler term "PC Card" for the version 2 specification.
[edit] Card types
All PC cards use same connecting interface with 68 pins. All are 85.6 mm long and 54.0 mm wide. The form factor is also used by the Common Interface form of Conditional Access Modules for DVB broadcasts. The 16 mm thick "Type IV" card, introduced by Toshiba, was not officially sanctioned by the PCMCIA.
The original standard was defined for both 5 volt and 3.3 volt cards. The 3.3V cards have a key on the side to protect them from being damaged by being put into a 5V-only slot. Some cards and some slots operate at both voltages as needed.
[edit] Type I
The original specification cards (version 1.x) are Type I and feature a 16 bit interface. Type I cards are used only for memory expansion. They had a single row of connector pins[citation needed] and are 3.3 mm thick. They are primarily used for adding RAM to a notebook PC.
[edit] Type II
The Type II PC cards featured a 16 or 32 bit interface, using two rows of pins. They are 5.0 mm thick. Type II cards introduced I/O support, allowing PC cards to attach an array of peripherals or to provide connectors/slots to interfaces the PC/laptop was not designed to support. For example, many modems or TV cards use this form factor.
[edit] Type III
The Type III PC cards are 16 or 32 bit, using four rows of pins. These cards are 10.5 mm in thickness, allowing them to accommodate larger connectors for peripherals without the use of "dongles", or short cables that allow a large connector to plug into a small card. Typically this accommodates for devices with components of the thickness that would not fit type I nor type II height like rotating mass storage devices (or portable disk drives - PDD).
[edit] CardBus
CardBus are PCMCIA 5.0 or later (JEIDA 4.2 or later) 32-bit PCMCIA cards, introduced in 1995 and present in laptops from late 1997 onward. CardBus is effectively a 32-bit, 33 MHz PCI bus in the PC card form factor. CardBus includes bus mastering, which allows a controller on the bus to talk to other devices or memory without going through the CPU. Many chipsets are available for both PCI and CardBus, such as those that support Wi-Fi.
The notch on the left hand front of the card is slightly shallower on a CardBus card so a 32-bit card cannot be plugged into a slot that can only accept 16-bit cards. Most new slots are compatible with both CardBus and the original 16-bit PC Card devices.
The speed of CardBus interfaces in 32 bit burst mode depends on the transfer type; In Byte mode it is 33 MBytes/s, in Word mode it is 66 MBytes/s, and in DWord mode it is 132 MBytes/s.
[edit] CardBay
CardBay is a variant added to the PCMCIA specification in 2001. This was intended to add some forward compatibility with USB and IEEE 1394, but was not universally adopted and only some notebooks support CardBay features in their PC Card controllers.
[edit] Descendants and variants
The interface has spawned a generation of flash memory cards that set out to improve on the size and features of Type I cards: CompactFlash, MiniCard and SmartMedia. For example, the electrical specification for the PC card is also used for CompactFlash, so a PC Card CompactFlash adapter need only be a socket adapter.
ExpressCard is a later specification from the PCMCIA, intended as a replacement for the PC card. PC Card Standard is closed to further development and PCMCIA strongly encourages future product designs to utilize the ExpressCard interface. However, many notebook computers as of late 2006 still ship with PC card capabilities, but newer models are shipping with only ExpressCard slots or neither slot type (leaving expansion to USB only).
There is no general backward or forward compatibility between ExpressCard and CardBus sockets. CardBus devices do not fit ExpressCard sockets and ExpressCard devices do not fit CardBus sockets. Because of the differences in the interfaces, there are no general purpose adapters possible between the two formats. Some ExpressCard devices that use only USB technology could operate in CardBay compliant CardBus sockets with a suitable physical format adapter.
