CableCARDs slide into the back of compatible cable boxes and DVRs. About the size of a thick credit card, these small devices decode encrypted digital cable information so that you're able to watch it on your TV.

What is a CableCARD?

A CableCARD is a tiny device that decodes encrypted digital cable information so that you're able to watch it on your TV. About the size of a thick credit card, a CableCARD plugs into the back of some Digital Cable Ready (DCR) components.

CableCARDs were originally intended for HDTVs as a substitute for a cable box. The idea was that you'd slide the CableCARD into the back of your TV, and it would give you access to your cable provider's programming. Using a CableCARD instead of a set-top box meant you'd have fewer A/V components taking up shelf space, plus one less remote control to worry about.

However, while CableCARD compatibility was fairly common in TVs a few years ago, it has virtually disappeared as TVs with built-in QAM tuners have become more popular. All the HDTVs we carry have a QAM tuner, so this is currently your best option if you'd like to get digital cable without a separate box taking up space.

CableCARDs and cable boxes

Today CableCARDs are generally found in cable boxes and DVRs. They've essentially become to cable boxes what access cards are to satellite receivers — small cards that plug into your set-top box to tell your provider what channels you're able to receive. This is the result of an FCC mandate which kicked in on July 1, 2007, requiring all newly manufactured digital cable boxes to be compatible with CableCARD. Now, the new law does not require cable companies to replace their existing inventories with CableCARD-compatible boxes, so it may be some time before cable companies deliver these boxes to consumers. But don't be surprised if your next cable box includes a CableCARD slot.

Types of CableCARDs

CableCARDs come in two varieties — single-stream and multi-stream, known as S-Cards and M-Cards, respectively. S-Cards can only tune in one channel at a time, so they don't allow things like picture-in-picture, or the ability to record one program while watching another if you're using a DVR. M-Cards, on the other hand, can tune in two channels simultaneously, so you don't lose the aforementioned features.

We mentioned the two types of cards just to make you aware of their existence, but it really isn't important to remember them. That's because CableCARDs are found almost exclusively in cable boxes at this point, so the next time you upgrade your cable box, it will come preloaded from your cable provider with whatever type of card you need. One possible exception would be if you purchased a stand-alone DVR like a TiVo® box. In this case, you would want to request an M-Card from your cable provider (or possibly two S-Cards, depending on the box you own) to enjoy the full capabilities of your DVR.

CableCARD 2.0 — upcoming 2-way functionality

CableCARD-compatible devices are currently one-way. They don't allow communication from your end back to the cable company, so you're not able to enjoy interactive program guides, pay-per-view programs, or Video-on-Demand. However, this could change at some point in the future with "CableCARD 2.0." CableCARD 2.0-certified cable boxes and DVRs would allow two-way communication, so you'll be able to enjoy many of the features you may have grown accustomed to with a conventional digital cable box.

Now, the term "CableCARD 2.0" refers to the host device and not the actual card. (CableCARDs themselves are and always were designed to support two-way functionality.) It's an important distinction, and here's why: If you currently have an older TV equipped with a CableCARD, your television can only receive a one-way stream. Since CableCARD 2.0 isn't an actual card, changing CableCARDs at some point in the future won't help. If you'd like to enjoy things like pay-per-view and Video-on-Demand with your current TV, you'll need to get a cable box or DVR that's capable of two-way communication.

How it works

While CableCARDs do more or less the same thing as a digital set-top box, the decryption process is a bit more complicated. Once the CableCARD receives the encrypted signal from your cable provider, there are three more steps before you can see video on your TV:

• Decryption: The CableCARD receives encrypted digital programming information and decodes it.
• Re-encryption: The CableCARD re-encrypts that decoded information and passes it on to the CableCARD-ready cable box or DVR, along with a decryption key.
• Decryption: The cable box or DVR receives the re-encrypted information and uses the decryption key to decode it.

Re-encryption is one way that cable providers prevent their service from being stolen. In order for the CableCARD to pass on the decryption key to your cable box or DVR, it has to be activated by your cable provider. Activation is what tells the CableCARD that it's OK to pass on the decryption key and allow you to watch the channels you subscribe to. It's a two-part process:

• Pairing: Matches the CableCARD to one specific cable box or DVR. Pairing tells the CableCARD that it's OK to pass on the decryption key for the channels that you're paying for.
• Authorization: Tells the CableCARD which channels you're paying for as part of your programming package, i.e. which ones you're authorized to watch. It will pass on the decryption key for those channels only to the cable box or DVR that it's paired to.