While legacy PCs (post IBM PC/AT) typically use 9-pin RS-232 plugs external modems are usually equipped with 25-pin RS-232 sockets * You can depend on Monoprice to have the cables you will need for this type of connection! This cable features a female DE-9 (DB-9) socket on one end and a male DB-25 plug on the other * The 9 pins of the DE-9 connector are wired to 9 of the pins on the DB-25 connector