VMware and Microsoft offer server versions of their virtual machine (VM) products. VMware offers two VM server products: VMware GSX Server and VMware ESX Server. (For more information about GSX Server, see "VMware GSX Server 2.5," July 2003, InstantDoc ID 39182.) Microsoft plans to release Virtual Server 2004 in the first half of 2004. The basic difference between the server-oriented VM products and their workstation counterparts is their respective purposes.

The workstation products are geared toward running legacy desktop applications and setting up testing and training scenarios. Although you can use the virtual server products to run legacy applications and test applications, their intended purpose is to let you consolidate multiple server OSs on one physical server, thus using computing resources more efficiently. The virtual server products support more processors and require more memory than their workstation counterparts and, as you might expect, are significantly more expensive. Compared with VMware Workstation 4, GSX Server and ESX Server provide better support for SMP systems, Storage Area Network (SAN) hardware, and remote management, and full support for Microsoft clusters. (No information about specific Virtual Server features was available at publication time.)

GSX Server and Virtual Server operate essentially the same way as the workstation products do. You install the VM software on a host OS. You then use the VM software to create VMs in which you install the guest OSs (most likely server OSs). ESX Server is structured differently from GSX Server and Virtual Server. ESX Server doesn't require a host OS, and you install it directly on the hardware. According to VMware, running ESX Server directly on the hardware without an OS helps ESX Server perform better than the virtual desktop products and GSX Server and enhances ESX Server's ability to consolidate multiple production servers. However, not surprisingly, ESX Server requires the host system to use only hardware that the product specifically supports.