PCI-Express is the latest type of expansion slot. Unlike the AGP and PCI buses which transfer data in a parallel fashion, PCIE offers serial data transfer. It is designed to be a point-to-point bus, and so it is not shared by other components. The bus is implemented as a pair, with two lanes per bus. So it can act in full duplex mode, meaning that data can be simultaneously sent and received over different lanes at full speed. It is also modular, in that the number of PCIE lanes can be increased or decreased based on the need of the device. So a PCIE x16 slot that has 16 lanes (8 lanes each for carrying data in one direction) can be used for graphics cards, while a slower PCIE x2 slot can be used for less demanding components like modems and sound cards. Each PCI-Express lane can transfer 2 Gigabits of data per second, which translates to 250 Megabytes per second.