Comcast Corp., seeking to match its competitors, is launching gig internet speeds for residential customers in East Coast markets, including Philadelphia.

Gig speeds, or one-gigabit-per-second, are about 10 times what the typical Comcast Xfinity internet customer now gets, enabling someone to download a two-hour movie in 40 seconds or a 30-minute television show in four seconds.

Comcast said Tuesday morning that one gig is now available in Boston and will be available later this summer in Philadelphia. Other areas slated for the service are Washington;  Baltimore; Harrisburg; Lancaster; and Charlottesville, Va.

RCN, a small cable company in Delaware County and the Allentown area, announced one-gig speeds last fall. Verizon Communications Inc. began offering them with FiOS.

Google said it would roll out one-gig speeds in markets around the nation, though it has retreated from those initial plans because of costs.

Comcast has priced one-gig speed at $104.95 a month, with an initial promotion of $79.99. The company said Xfinity customers might have to upgrade their modems. The service will be marketed as the "gigabit plan."

Download speed with the new service — which is what most people care about — will be one gig. But the upload speed will be 35 megabits per second because of the architecture of the cable network. So it will be much slower to send data such as video, or upload it, than to download it.

"We have been on a pace of doubling our network capacity every 18 to 24 months, ensuring that we stay well ahead of demand," said Tracy Pitcher, a Comcast senior vice president in the Boston region.

Most Comcast customers won't need gig speed. But the belief is that as consumers use multiple smartphones and tablets in homes, in addition to laptops, for Facebook, gaming, or online video, they will need the super-fast speeds for smooth connections.