Final answer:
PCI Express uses a serial bus architecture, which allows for higher speed and more efficient data transfer compared to the traditional parallel bus.
Step-by-step explanation:
The type of bus that PCI Express (Peripheral Component Interconnect Express) uses is serial. Unlike its predecessor, the PCI bus, which used a parallel bus architecture, PCI Express uses a high-speed serial connection. This advancement allows for each lane of the bus to carry data independently at a much higher rate, increasing the overall performance and speed of data transfer between the motherboard and attached devices, like graphics cards and SSDs.