external (line) sources. Most iRiver players include a unique feature called study mode. Users can quickly jump back and forth within tracks by a certain time interval, set from three to 180 seconds in current models. The option was designed to help people listening to recorded language lessons. SonicBlue removed this feature from its rebranded Rio Volt models, causing some users to hack their players with iRiver firmware from other regions. Initially connecting devices to the computer for music transfer required the iRiver Music Manager. In later firmwares UMS is supported so that the computer's native file explorer could be used to transfer files. Iriver eventually dropped UMS support for the U10, T30, T20 and T10 models in favor of Microsoft's MTP. The company later released an official Firmware Updater that allows users to switch between the MTP and UMS interfaces. Hard disk based iGP series iGP-100 (1.5GB) USB 2.0 connectivity. Plays MP3, WMA, ASF, and Ogg Vorbis files. UMS. Built in lithium-ion battery. Released in 2003. H/iHP series H10: (5 GB, 6 GB, 20GB—except Asia), available in 4 different colors (red, blue, silver and grey), 16-bit color screen, can record from Radio, Internal Microphone (Voice) or Line-In (Line in only with extra cradle). The 5 GB and 6 GB models are around the size of the iPod mini and are composed mainly of aluminum. The navigation is done with a touchpad designed by iriver. These devices cannot play Ogg Vorbis files. PlaysForSure and UMS. iHP-100 series: (10 GB, 15 GB, 20 GB, 40 GB) Voice, line in and FM recording. Optical in and out. Built in lithium-polymer battery. UMS. USB 2.0 connectivity. H300 series: (20 GB, 40 GB) PlaysForSure and UMS. Built in lithium-polymer battery. Transfer with certain Digital Cameras. Voice, line in and FM recording. Plays video with Korean firmware. USB 2.0 connectivity. E series E10: (6 GB) Similar interface to that of the U10 series. The device also features a remote control for TV. PlaysForSure and UMS are supported. The device allows flash files to be played, videos and FM radio. It contains recording capabilities for both voice and FM radio. Released 2006 in Japan and South Korea, elsewhere in 2007. Flash memory based iFP series iFP-100 (Prism): (32 MB, 64 MB, 128 MB, 256 MB, 512 MB) Prism shaped. USB 1.1 connectivity (four-pin mini-B plug). Plays MP3, WMA and WAV files. Prism shaped. MTP (UMS upgradable).