What Is a Modem? (Modem vs Router)

by Priya Nakamura Updated Apr 12, 2026

A modem (modulator-demodulator) is the device that connects your home to your Internet Service Provider (ISP). It converts the ISP's signal (cable, DSL, or fiber) into data your home network can use.

Types of Modems

Cable modems connect via coaxial cable (Comcast, Spectrum). DSL modems use phone lines (AT&T, CenturyLink). Fiber modems (ONTs) use fiber optic cables (Verizon Fios, Google Fiber). Each type only works with its corresponding ISP technology.

Modem vs Router vs Gateway

A modem connects to the ISP. A router creates your home network. A gateway combines both into one device. If your ISP gave you one box that provides both internet and WiFi, it's a gateway.

Related Guides

Video Tutorial

For more information, see Wikipedia — TCP/IP.

Pro Tip: DNS is often called the phonebook of the internet. Switching to a faster DNS can improve your perceived internet speed significantly.

Key Takeaways

Private IPs (192.168.x.x, 10.x.x.x) are used inside your home network
DNS translates domain names to IP addresses
DHCP automatically assigns IPs so you don't have to
Your default gateway is your router's IP address

Frequently Asked Questions

What does a modem do?

A modem converts your ISP's signal into digital data and vice versa, providing the physical connection between your home and the internet.

Can I use my own modem?

Usually yes. Buying your own modem can save $10-15/month in ISP rental fees. Check your ISP's compatible modem list before purchasing.

About Priya Nakamura

Priya is a telecommunications engineer and networking educator at RouterHax. With a background in ISP infrastructure and a Master's in Computer Networks, she explains complex networking concepts in plain English. Priya covers WiFi standards, protocols, IP addressing, and network architecture.