Comcast Platinum Plan: Download HD Movie in 20 Mins

Comcast has unveiled what may be the fastest broadband service ever offered to home users: a maximum speed of 305 megabits per second (Mbps). It's a plan that will cost subscribers $300 a month.

The new package is part of Comcast's program to increase the speed of its fastest packages, including Xfinity Blast at 50 Mbps, Xfinity Extreme at 105 Mbps, and the new Xfinity Platinum at 305 Mbps.

The slightly odd number (305 Mbps) has clearly been chosen to beat out rival Verizon's premium package, which tops out at 300 Mbps. The Verizon service is cheaper -- $205 a month -- but requires a two-year contract, unlike Comcast's plan.

Comcast's new Xfinity Platinum offering is limited to certain markets, mostly in northeastern US cities. This is because Comcast is willing to upgrade its cables only when it sees a lot of potential customers. (Source: pcmag.com)

Fast Broadband in Practice

To judge the speed of Xfinity Platinum, consider that it can provide 38 megabytes of data per second, enough to download a complete DVD movie in less than four minutes, or a Blu-ray-quality film in just over 20 minutes.

In practice, however, there are significant limitations to the service. For example, it will offer little noticeable improvement when users are surfing the web. And when downloading large files, a computer's maximum speed is often limited by the website's ability to provide the data.

Another limitation is that 300 to 305 Mbps connections are about three times faster than existing home WiFi network maximums, limiting the full benefit to devices connected by wire to their network routers.

Comcast Targets Multi-User Households

Because of these limitations, Comcast is marketing the service to "really advanced digital families," where multiple users may be online at the same time. (Source: bloomberg.com)

These faster services could become particularly vital as more people in a household simultaneously use the Internet for TV, movies, and other large files, such as watching a Netflix movie, following a live sports event stream, checking out YouTube clips, and downloading a game.

Even with everyone online at once, no one should notice any degradation in service quality.

However, while these faster services may be appealing, it's still unclear how many families will pay $200 to $300 a month for them.