Networks are sometimes defined by the nature of the content they carry. For example, some networks capable of sustained high-bandwidth connections are dedicated to video and other multimedia, whereas others are limited to text. Networks may also be relegated to database or equipment communications. The former is especially prominent in bioinformatics, in the form of storage area networks. These networks, typically based on fiber optics, are maintained for high-speed communications between disk arrays and computers involved in sequencing and other applications that require almost constant access to data stored on high-speed hard drives.