A write head is a compontent of many magnetic storage devices. The write head passes over the storage media, like a tape or disk, and uses an electrically generated magnetic field to change the magnetic properties of the media. The changes are made so that the arrangement of the magnetic differences are recognizable by the read head. Reading is usually a function which the write head can perform. In a cassette recorder or a tape hard-drive, there is usually only one read/write head providing only sequential access to data on the tape. In a conventional disk drive there are often multiple heads (one for each disk) which are capable of random access because they can move back and forth across the disk as well as forwards. Just like a CD or a record, they can skip to any area on the disk in minimal time.