What type of data does a modem modulate onto an analog carrier for transmission?

A modem primarily modulates digital data onto an analog carrier for transmission. This process allows digital devices, like computers, to communicate over traditional telephone lines, which are inherently analog. The modulation process converts the digital signals from the devices into a format that can be transmitted over the analog medium, ensuring that the information can be sent and received accurately over these lines.

In this context, while analog data indeed exists, it is not the primary function of a modem. The process specifically involves the interaction between digital data from a computer and an analog carrier, highlighting the modem's role in bridging the two types of signals.