The TOPS local area network enables the Macintosh, PC/MS Dos, and UNIX-based computers to directly share disks, files and peripherals in real time. TOPS networks can consist of a single operating system, or any combination of supported systems. For example, the TOPS cross-operating system translation allows a Macintosh user with MicroSoft Excel to open a Lotus 1-2-3 file located on a remote IBM PC, alter it, and store it back on the PC. TOPS also provides full security to protect against unauthorized access. TOPS PRINT allows PC users to print directly to a shared Apple Laserwriter. Centram's newest product TOPS REPEATER increases the size and length of AppleTalk networks, giving users greater flexibility in their network topology.