(Jeff Fusco/AP Images for Comcast)

Comcast has just released some new details about its future-ready answer to Google Fiber and Verizon FiOS. Beginning in the first half of the year, Atlanta and Nashville will be the first cities to take advantage of a new technology that enables gigabit speeds over traditional cable connections.

That will be followed in the second half of the year by gigabit cable service in Chicago, Detroit and Miami, Comcast said Tuesday. Gigabit Internet, which is available from a number of providers across the country already, offers download rates of 1,000 Mbps — far faster than what many Americans currently receive. At those speeds, you could download an HD movie in about 7 seconds. Internet providers have been racing to roll out faster speeds in light of new entrants such as Google Fiber, whose parent company, Alphabet, just became the world's most valuable company.

What sets Comcast's new offering apart from the competition is that it relies on an upgrade of existing cable technology, rather than requiring a shift to expensive high-speed fiber optic cables, which are made of glass and transmit data as pulses of light. In other words, rather than building a whole new fiber infrastructure like Google Fiber is doing, Comcast can take advantage of the cables that are already in the ground to provide gigabit speeds. This is good for Comcast, because it means offering a similar service as Google's but at a lower upfront cost to itself; whether it means those savings will be passed on to consumers is another question.

[Why Comcast may be poised to win the Internet speed race]

Here's the catch: Customers who sign up for the service will have to swap their cable modems for new ones that support the fresh tech, known as DOCSIS 3.1. You can keep your existing modem if you prefer not to sign up for the gigabit service.

Comcast won't say just yet how much its gigabit cable service will cost. But we can guess.

The company does operate a fiber optic Internet service of its own, called Gigabit Pro. That offering enables speeds of up to 2 Gbps, or 2,000 Mbps. For that, Comcast charges $300 a month, in addition to installation fees.

In light of the gigabit cable service's slower download speed, it's probably safe to predict that Comcast will be charging subscribers somewhat less.