Editing PC Card (section)

== Bus ==
[[file:PCCard CardBus.jpg|thumb|Left: connector of a 16-bit ISA-based PC Card. Right: connector of a 32-bit PCI-based CardBus PC Card. Usually, CardBus PC Card slots are compatible with the ISA-based PC Cards, but not the other way around.]]

=== Original ===

The original standard was defined for both 5&nbsp;[[volt|V]] and 3.3&nbsp;volt cards, with 3.3&nbsp;V cards having a key on the side to prevent them from being inserted fully 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 [[Industry Standard Architecture|ISA]] bus platform. A newer version of the PCMCIA standard is CardBus (see below), a 32-bit version of the original standard. In addition to supporting a wider bus of 32 bits (instead of the original 16), CardBus also supports [[bus mastering]] and operation speeds up to 33&nbsp;MHz.

=== CardBus ===

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&nbsp;MHz [[Peripheral Component Interconnect|PCI]] bus in the PC Card design. CardBus supports [[bus mastering]], which allows a controller on the bus to talk to other devices or memory without going through the [[Central processing unit|CPU]]. Many chipsets, such as those that support [[Wi-Fi]], are available for both [[Conventional PCI|PCI]] and CardBus.

The notch on the left hand front of the device is slightly shallower on a CardBus device so, by design, a 32-bit device cannot be plugged into earlier equipment supporting only 16-bit devices.  Most new slots accept both CardBus and the original 16-bit PC Card devices. CardBus cards can be distinguished from older cards by the presence of a gold band with eight small studs on the top of the card next to the pin sockets.

The speed of CardBus interfaces in 32-bit [[Burst mode (computing)|burst mode]] depends on the transfer type: in byte mode, transfer is 33&nbsp;MB/s; in word mode it is 66&nbsp;MB/s; and in dword (double-word) mode 132&nbsp;MB/s.

=== CardBay ===

CardBay is a variant added to the PCMCIA specification introduced in 2001.  It was intended to add some forward compatibility with [[USB]] and [[IEEE 1394]], but was not universally adopted and only some notebooks have PC Card controllers with CardBay features. This is an implementation of Microsoft and Intel's joint [[Drive Bay]] initiative.