More Information About PC_card
In computing, PC Card (originally PCMCIA, or PCMCIA Card) is the form factor of a peripheral interface designed for laptop computers. The PC Card standard (as well as its successor ExpressCard) were defined and developed by a group of industry-leading companies called the Personal Computer Memory Card International Association (PCMCIA). The United States computer industry created the Personal Computer Memory Card International Association to challenge the Japanese JEIDA memory card devices by offering a competing standard for memory-expansion cards. In 1991 the two standards merged as JEIDA 4.1 or PCMCIA 2.0 (PC Card).
PC Card was originally designed for computer memory expansion, but the existence of a usable general standard for notebook peripherals led to many kinds of devices being made available in this form. Typical devices included network cards, modems, and hard disks. The cards were also used in early digital SLR cameras, such as the Kodak DCS 300 series. The original use, as memory expansion, is no longer common.
Many notebooks in the 1990s came with two type-II slots with no barrier in between (allowing installation of two type-II cards or one, double-sized, type-III card). With the removal of legacy ports, most contemporary notebooks only feature a single type-II card slot.[citation needed]
Two PC Card devices: Xircom RealPort (top) type III and 3Com (bottom) type II.
Name
PCMCIA stands for Personal Computer Memory Card International Association, the group of industry-leading companies that defines and develops the standard. While this acronym did clearly describe the original intentions of the organization's standard, it was difficult to say and remember, and was sometimes jokingly referred to as "People Can't Memorize Computer Industry Acronyms".[1] To aid in the widespread marketing and branding of the standard, and to account for the standard's widening scope (beyond just memory cards), the association acquired the rights to the simpler term "PC Card" from IBM, and began using it, rather than "PCMCIA", from version 2 of the specification onwards.
Card types
All PC Card devices use an identical 68 pin dual row connecting interface. All are 85.6 mm long and 54.0 mm wide. This is the same size as a credit card. The form factor is also used by the Common Interface form of Conditional Access Modules for DVB broadcasts.
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.
Type I
Cards designed to the original specification (version 1.x) are type I and feature a 16-bit interface. They are 3.3 mm thick. Type-I PC Card devices are typically used for memory devices such as RAM, flash memory, OTP, and SRAM cards.
Type II
Type-II PC Card devices feature a 16- or 32-bit interface. They are 5.0/5.5 mm thick. Type-II cards introduced I/O support, allowing devices to attach an array of peripherals or to provide connectors/slots to interfaces for which the host computer 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.
Type III
Type-III PC Card devices are 16-bit or 32-bit. 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).
Type IV
Type-IV cards, introduced by Toshiba, have not been officially standardized or sanctioned by the PCMCIA. These cards are 16 mm thick.
Card Information Structure
The Card Information Structure (CIS) is information stored on a PC card that contains information about the formatting and organisation of the data on the card.[2] The CIS also contains information about:
- The type of card
- Supported power supply options
- Supported power saving features
- The manufacturer
- Model number
- and so on.
When a card is unrecognised it is frequently because the CIS information is either lost or damaged.
CardBus
Two Xircom RealPort Ethernet/56k modem cards. Top one is CardBus, and the bottom is the 5 volt PCMCIA version. Note the slightly different notch.
CardBus are PCMCIA 5.0 or later (JEIDA 4.2 or later) 32-bit PCMCIA devices, 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 device is slightly shallower on a CardBus device, so a 32-bit device cannot be plugged into a slot that can only accept 16-bit devices. 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.
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.
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 PC Card electrical specification 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 PC Card, built around the PCI Express and USB 2.0 standards. The 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), though the Lenovo Thinkpad T60 and Z60m, among other models, currently ships with both CardBus and ExpressCard slots.
ExpressCard and CardBus sockets are physically and electrically incompatible. Therefore, a simple mechanical adapter between the two formats is infeasible.[3] However, Duel Systems has developed a general-purpose adapter that electrically and physically adapts PC Card and CardBus devices to operate in ExpressCard slots.[4] Duel Systems has also developed a forwards-compatible adapter for USB-based ExpressCard devices in CardBus slots.[5]
Technological obsolescence
Firewire and USB devices are available for almost all functions that the PC Card interface was used for in the past, although it retains the advantage of containing devices entirely or almost entirely inside the case of the portable device. This can be an important consideration for portable systems, where additional external peripherals and their associated cables, space, and sometimes additional power supplies can reduce portability and convenience. However even in this case ExpressCard devices have the same advantages as PC Card devices, with additional bandwidth & functionality. On the other hand many devices do not need the speed of PCI Express, and often PC Card devices with adequate performance can be found cheaply, as discounted new parts or on the used components market, and will suffice for many users' purposes.
See also
References
- ^ Clark, Scott H.; Norton, Peter (2002). Peter Norton's new inside the PC. Indianapolis: SAMS, 33. ISBN 0-672-32289-7.
- ^ Linux PCMCIA Programmer's Guide
- ^ PCMCIA Frequently Asked Questions.
- ^ DP-0001 from duel-systemsadapters.com
- ^ DP-0002 from duel-systemsadapters.com
External links
Related and official sites
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