Direct-attach copper (DAC)
Beginner
A plain copper cable with a plug on each end and no chips inside.
Novice
A passive cable of twin-axial copper pairs with a module-shaped plug on each end. The switch chip’s own SerDes drives the signal straight through it. Cheapest and lowest power, but only a meter or two at today’s speeds.
Expert
Passive twinax assembly (for example 802.3ck CR or 802.3dj CR PHYs). The host SerDes must equalize host traces, connectors and cable together; reach falls as the lane rate rises (about 2 m at 100G per lane, about 1 m at 200G).
Explained in Optics (Systems).
See also: Active electrical cable (AEC), Insertion loss.