Another term for the expansion slots on a computer’s motherboard is bus slots. A number of different bus architectures have been developed over time. For the A+ exams, you need to be able to identify the differences between each of these bus architectures and know which ones are more popular today.

Architecture Bus Width (In Bits) Speed
ISA 8/16 8 MHz
MCA 32 10 MHz
VLB 32 Speed of local bus
EISA 32 8 MHz
PCI 32/64 33 MHz
AGP 32 66 MHz (1x), 133 MHz (2x), 266 MHz (4x), 533 MHz (8x)
PCMCIA (laptops) 16 33 MHz
PCI-X 32/64 66/133/266/533 MHz
PCIe Serial Uses multiple lanes, with each lane carrying 250 Mbps. As an example, a PCIe x1 slot can carry data at 250 Mbps, while a PCIe x4 slot can carry data at 1 Gbps. PCIe version 2 doubles those transfer rates.