Depending on the quality of the media you are using, a gigabyte of storage can hold anywhere from several hours of video to just a few minutes. At standard TV quality, it can store approximately an hour of video. However, at HDTV quality, it will only store approximately 7 minutes. This is why a DVD can store an entire movie on either a 4.7 GB disc or an 8.5 GB dual-layered disc, while a Blu-ray needs 25 – 50 GB to store the same film. Likewise, you can store slightly more than 100 minutes of CD-quality audio using 1 GB of storage, but when compressed to MP3 format, you can store hundreds of minutes in the same amount of space. The average book takes up approximately 1 megabyte of storage, so a gigabyte of storage can hold approximately 1,000 books.