So far, this guide has covered video standards (technical specifications for broadcasting, such as NTSC and ATSC) and "modes" (the record and playback settings for HD, 1080i, 720p, 1080p). Formats are carriers of video information, the devices and/or software that contain video data. As with standard definition video, most HD formats fall into three categories: videotape, optical media and digital files. The most common formats encountered in museum collections are listed below.