Editing PC Card (section)

=== 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 A newer version of the PCMCIA standard is CardBus (see below), a 32-bit version of the original standard.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.