You have to hand it to TiVo -- the company revolutionized the way millions of people consume television. Before digital video recorders (DVRs) like TiVo, we relied on VCRs to record programs we planned to watch later. But recording onto video tape could be complicated depending upon the brand of VCR.
A good digital video recorder will have a simple (but deep) user interface and other features that make it easy to record television programming. But a normal DVR may not be able to record programming in HD format. For that, you'll need a special kind of DVR.
High-definition television programs pack hundreds of thousands of pixels into every second of the show. Storing a program in HD format requires a much larger hard drive to accommodate the extra information in an HD signal. You'll need an HD DVR if you want to record and watch the channels you get in an HD format.
Even with an HD DVR, you'll find that your recorder can only hold a fraction of HD programming compared to regular programming before it reaches capacity. For example, a 180-hour HD TiVo can only store 20 hours of HD content. Boxes with a larger hard drive can hold more hours of programming. The nice thing about DVRs is that you can always delete older content to make room for new shows.
With the right setup, you'll even be able to record multiple HD shows at the same time. This is great for those days when all the shows you enjoy watching seem to be on at once. Or you can watch one channel while recording another. And DVRs allow you to skip commercial breaks! People who become accustomed to having a DVR often find it difficult to revert back to watching television without one.