The Socket 603 and 604 are designed for Xeon-series, which are used in workstations and servers use. They possess the type PGA ZIF and a AGTL + bus protocol. While Socket 603 only support clock frequencies up to 100MHz, Socket 604 works even with clock frequencies up to 200MHz. The sockets associated with Socket 603 processors operate at clock speeds between 1.4GHz and 3.2GHz, sockets associated with Socket 604 corresponding socket turn clock speeds between 1.6GHz and 3.8GHz. Although Socket 603 CPUs are mechanically and electrically compatible with Socket 604 motherboards, the reverse is not the case, since Socket 604 have an additional contact pin. Socket 603 is considered especially robust and inexpensive alternative to the Socket 604.