A universal serial bus (USB) plug-in card module supports the firm's ST Multi-User/Multi-Platform KVM Switch to allow computers with USB connectors for keyboard and mouse to attach to its line of ST switches. KVM (keyboard, video and mouse) switches allow the control of multiple computers with only one keyboard, monitor and mouse. Up to eight users can simultaneously access and control 32 computers across multiple platforms, eliminating the need for switches dedicated to each platform. Each switch has vacant slots for the number of users and computers specified. Switches are populated with the user's choice of Plug-In modules for their configuration of PC, Macintosh, and Sun computers. Modules can be added or changed later as needs change. The KVM Switch is PS/2 compatible with computers such as laptops, RS6000, SGI, HP9000, Sun computers including Ultras, Macintosh Duo Docks, G3s and Macintoshes with dongle devices. Users can expand up to 512 computers by combining the ST-MX with the ST units.