How Devices Connect (USB, PCIe, GPUs & Peripherals)

How the outside world and expansion cards plug into a computer: the USB host/device model, the PCIe highway inside the case, and how GPUs and everyday peripherals present themselves to the system.

1. USB & the Host/Device Model USB has one host (the computer) in charge of many devices; plugging something in triggers enumeration - the host detects the device, asks what it is, and loads a driver. Hubs let one port branch into many, and USB's confusing names describe speed and a connector shape, not the same thing.
2. PCIe - the High-Speed Internal Highway PCIe is the fast expansion bus inside the case. It moves data over lanes - independent parallel pairs of wires - and slots are sized by how many lanes they carry (x1, x4, x8, x16). Lane count sets bandwidth; the generation sets the speed per lane. GPUs, NVMe SSDs, and network cards all plug in here.
3. GPUs & Peripherals A GPU exists to do massively parallel work - graphics and now machine learning - and connects over PCIe, where feeding it data is often the real bottleneck. Everyday peripherals (keyboard, mouse, display, webcam) present themselves through standard device classes, so one generic driver can handle thousands of models.