O que é PCI Express, direct memory access?

PCI Express (PCIe) is the serial point-to-point bus that connects devices (network cards, storage, accelerators) to a processor socket, in lanes grouped by 1 to 16. In direct memory access (DMA) a device reads and writes host memory itself, without the processor copying each byte: a network card writes each received packet into a buffer the driver gave it and signals its arrival by a descriptor, an interrupt or a flag the program polls.