Microsoft last week stepped into the virtualization market dominated by VMware with the introduction of Virtual Server 2005.The product, which it acquired from Connectix in 2003, allows network administrators to divide a server into partitions for consolidation or migration purposes.Server virtualization on Intel or Opteron processor-based servers comes in three forms. Products such as Virtual Server 2005 and VMware's GSX Server consist of software that sits between the hardware and the operating system; they tend to be less scalable and secure than other implementations. VMware's ESX Server uses software developed by IBM that provides enough abstraction to effectively isolate and manage partitions from each other. Products like SW-Soft's Virtuozzo actually tweak the Linux kernel to achieve virtualization of a server's processors.Virtualization technology allows customers to run multiple instances of Windows, Linux or NetWare on servers. In Microsoft's case, the company will support Windows operating systems in virtual partitions, but not NetWare or Linux. VMware on the other hand will support all three.Microsoft says it is aiming for three markets with the release of Virtual Server 2005 - test and development, server consolidation and legacy system re-hosting. In legacy system re-hosting, Microsoft hopes to be able to migrate some Windows NT customers to Windows Server 2003.Microsoft's Virtual Server 2005 is available in two editions, Standard and Enterprise. The Standard Edition costs $500 per server, irrespective of the number of partitions or processors. The Enterprise Edition costs $1,000.By contrast, VMware's GSX server starts at $5,000 for a four-processor server. VMware rationalizes the higher cost by claiming that GSX server contains management software that Microsoft's Virtual Server 2005 does not.