PC card
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In computing, PC card (originally PCMCIA card) is the form factor of a peripheral interface designed for laptop computers. It was originally for memory expansion, but the existence of a usable general standard for notebook peripherals led to all manner of devices being made available in this form. Typical devices include network cards, modems and hard disks.
Many notebooks used to come with two Type II slots with no barrier in between (allowing two type II cards or one type III card). With the removal of legacy ports, most modern notebooks only feature one Type II card slot.
PCMCIA cards were designed by the US computer industry to compete with the Japanese JEIDA cards. The two standards later merged as JEIDA 4.1 or PCMCIA 2.0 (PC Card) in 1991.
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[edit] Name
PCMCIA stands for "Personal Computer Memory Card International Association". While this acronym did clearly describe the organizations initial intentions it was difficult to say and remember and was sometimes jokingly referred to as "People Can't Memorize Complicated Industry Acronyms" . To aid in the widespread marketing and branding of the standard and to account for the standards widening scope (beyond just memory cards) the association acquired the rights to simpler term "PC Card" from IBM and began using it (rather than "PCMCIA cards") from version 2 of the specification onward.
[edit] Card types
All PC cards use an identical 68 pin connecting interface. 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 3.3 V cards have a key on the side to protect them from being damaged by being put into a 5 V-only slot. Some cards and some slots operate at both voltages as needed. The original standard was built around an 'enhanced' 16-bit ISA bus platform.
[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 feature 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 for which the PC/laptop had no built-in support. For example, many modem, network and TV cards use this form factor. Due to their thinness, most type II interface cards feature miniature interface connectors on the card which are used together with a dongle; a short cable that adapts from the card's miniature connector to an external full-size connector.
[edit] Type III
The Type III PC cards are 16 or 32 bit, using two rows of pins. These cards are 10.5 mm thick, allowing them to accommodate devices with components that would not fit type I or type II height. Examples are hard disk drive cards, and interface cards with full-size connectors that do not require dongles (as is commonly required with type II interface cards).
[edit] Type IV
Type IV is not an official standard, though some PC Cards come in this format.
[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 MB/s, in Word mode it is 66 MB/s, and in DWord mode it is 132 MB/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, built around the PCI Express standard. PC Card Standard is closed to further development and PCMCIA strongly encourages future product designs to utilize the ExpressCard interface. As of 2007, the majority of laptops now ship with only ExpressCard slots or neither slot type (leaving expansion to USB and Firewire only), with only some entry-level models built around outdated chipsets still carrying PC-Card slot(s) .
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.
[edit] See also
[edit] External links
- Personal Computer Memory Card International Association
- Linux PCMCIA Information Page (kernel 2.4 and earlier)
- Linux Kernel 2.6 PCMCIA
- PCMCIA/CardBus Linux Status Survey
- PCMCIA pinout
| Memory cards |
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| CompactFlash (CF) | JEIDA | Memory Stick | MultiMediaCard (MMC) | PC card | SmartMedia | Secure Digital (SD) | xD-Picture Comparison of memory cards |
