kHz tone is also occasionally used for North American reception, but this configuration is not compatible with European-style universal LNB's which use the tone internally for band-switching. A toroidal antenna may be used with multiple LNB's to receive multiple satellites in various locations over a 40° arc. Unlike the single parabola of a standard satellite dish antenna (which is best adapted to focus one target satellite to a single point), the toroidal antenna uses a reflector pair to focus multiple signals to a line. Individual adjacent or near-adjacent pairs (such as Glorystar on 97°W and 101°W) may be received, due to their close proximity, with two LNB's on what otherwise looks geometrically to be a standard parabolic dish. The outputs from these individual LNB's may then be fed through a switch to a receiver, providing access to all signals on both satellites. Electronic program guide An on-screen program schedule can be accessed that also contains descriptive information about a selected program. The availability and quality of programme guide information varies widely between broadcasters (some provide nothing) and the ability of receivers to collect and store guide listings from multiple sources is also variable. Receivers with more memory (or storage on external devices such as hard drives) are often, but not always, better equipped to store and retrieve on-screen programme listings. In some cases, a receiver with both satellite and terrestrial tuners will provide on-screen guide support for one mode of operation but not both. PVR functions A few high-end receivers feature the ability to record programs, pause, and review live TV. Often, a hard drive is not included when the unit is purchased, which allows the user to install any desired hard disk drive. Many newer units are equipped with a USB 2.0 port that allows the user to connect a portable hard drive; at least one unit (the Pansat 9200HD) uses external SATA as PVR media storage. Some receivers, such as TripleDragon or Dream Multimedia's Linux-based Dreambox series, provide local area network interfaces. This allows the use of network-attached storage to provide PVR-like functions (some of these models also include internal hard drives or USB) and allows the unit to be controlled or updated via network. The use of desktop personal computer cards to deploy DVB-S or terrestrial digital television tuners allows the computer's hard drive and network storage to be used to archive electronic programme guide information and