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.