Pentium 90 MHz or faster, or Digital Alpha 4/275 (Pentium 166 MHz or faster, or Digital Alpha 5/500 recommended) Microsoft Windows NT, NT Server version 4.0 or later, and Service Pack 3 24 MB RAM (32 MB recommended, 48 MB for RISC-based systems) 250 MB hard disk space, plus sufficient disk space for the Windows NT Server page file CD-ROM driver Additional prerequisite software for some applications Note: If you install Microsoft Exchange Server on a pair of clustered servers, the processors and amount of RAM must be the same on each server. If you are adding a server to an existing site, verify that there is enough space on the server's hard disk to import the site's directory