Microsoft Corp.'s Virtual Server 2005 is probably best viewed as a direct competitor to VMware's well-entrenched GSX Server, but the degree to which Virtual Server integrates with other Microsoft server products puts it in a class of its own. To test the product, I configured a variety of systems. The primary server bank was a pair of dual-processor AMD Inc. Opteron rack servers, one with 4GB of RAM and one with 8GB. I focused on the Opterons because both Microsoft and VMware have adapted their products to run on Opteron with enhanced capabilities. With the exception of memory, Virtual Server 2005's system requirements are easy to meet. Windows Server 2003 is the only supported host OS, so its hardware compatibility list sets the rules. Virtual Server 2005 Standard Edition works with as many as four CPUs, whereas the Enterprise Edition supports an unlimited number of processors in a single machine. RAM is the most significant requirement.