The Physical and Data Link Layers

The OSI model starts at the bottom with the parts closest to the hardware. Layer 1 is the physical layer and Layer 2 is the data link layer. Together they get raw bits onto a medium and deliver them reliably to the next device on the same local network. These two layers are the foundation everything else rests on, turning electrical or light signals into usable frames.

The physical layer deals with the actual transmission of bits as signals. It covers cables, connectors, voltage levels, light pulses, and radio waves. Its only concern is moving raw 1s and 0s across a medium; it does not understand addresses or meaning. Anything you can physically touch, like a cable or a port, lives at the physical layer.