An umbrella term for a variety of handheld devices that play back audio, video or both. The device may also serve as a portable photo album for still images such as GIFs and JPEGs. The term "media player" without the "portable" typically refers to software (see media player), but may refer to the hardware devices mentioned here. Flash Memory and Hard Disk (MP3 and MP4) Audio-only MP3 players, which use flash memory (solid state) or hard disk for storage, are the most popular portable media devices. In addition to MP3, they typically support one or more other audio formats such as WMA and AAC. See digital music player. An "MP4 player" or "video MP3 player" refers to a combination audio/video device such as the full-size iPod or a Portable Media Center device, which is bigger and has a larger screen. See iPod. Optical Discs and Tape Cassettes Although used less frequently, handheld DVD, CD and tape cassette players also fall into the portable media player category. See portable DVD player and direct media access.