A modem is a device that modulates signals for data transmission. It converts digital data from your computer into signals that can travel over phone lines, cable, or fiber, and converts incoming signals back into digital data. The word is a contraction of modulator and demodulator.

Early modems used phone lines and made screeching sounds. Speeds were measured in bits per second, starting at 300 bps in the 1960s. DSL and cable modems replaced them, offering megabits per second. Fiber modems, called ONTs, handle gigabits. Satellite modems serve remote areas.

Types of modems

• DSL: uses telephone lines
• Cable: uses coaxial TV lines
• Fiber: uses optical signals
• Satellite: uses radio links to orbit
• Cellular: uses mobile networks

Most people rent a modem from their internet provider. Buying your own can save money, but compatibility varies. The modem is the bridge between your home network and the internet. When it fails, everything goes dark.