The most common cards are s-cards. Tivo HD will permit both tuners if you have TWO cards or NO cards. With one card it acts as a single tuner. You will be able to watch/record only one station (regardless of source). You will be able to watch a recorded show while Tivo is recording another.
The Comcast stated policy is that the first card is free, and the second is a "nominal" cost. In most areas that cost is $1.50 to $2.75 per month.
There is also an m-card that is just beginning to show up in some Comcast regions. A single m-card in the Tivo HD will permit the use of two tuners and give complete functionality.
You'll have to contact your local Comcast to get pricing and avialability of the m-card.
The Comcast stated policy is that the first card is free, and the second is a "nominal" cost. In most areas that cost is $1.50 to $2.75 per month.
There is also an m-card that is just beginning to show up in some Comcast regions. A single m-card in the Tivo HD will permit the use of two tuners and give complete functionality.
You'll have to contact your local Comcast to get pricing and avialability of the m-card.