Windows NT Server 4.0 Editions
If you're familiar with the editions of Windows NT Server 4.0, selecting the appropriate edition of Windows Server 2003 might be easier with a quick review of the 4.0 editions and a comparison to their Server 2003 counterparts.
Windows NT Server 4.0's basic edition is simply called Windows NT Server 4.0. It supports a maximum of four processors per computer, a maximum of 4GB of physical RAM per computer, and a maximum of about 4TB (terabytes; 1 terabyte is equal to 1,000 gigabytes) of disk space. The basic edition provides a 50/50 split of server memory, reserving 2GB of RAM for the operating system and 2GB for applications. Windows Server 2003, Standard Edition roughly corresponds to NT 4.0's basic edition because it has the same basic memory, processor, and disk space limitations.
Windows NT Server 4.0 Enterprise Edition introduced Windows Clustering. Actually, it introduced two types of clustering: the Windows Load Balancing Service (WLBS) and true Windows Clustering, which had been code-named Wolfpack. In WLBS, multiple servers hosting the same content distribute incoming user requests across themselves. The most common WLBS scenario is Web farms, in which many different identical Web servers handle incoming requests from Internet users. True Windows Clustering uses the Windows Cluster Service and allows two servers to provide failover and redundancy for one another. The clustered servers, called nodes, don't balance their workloads between themselves. Instead, each node does its own independent work. If one node fails then the other node picks up and does its own work along with the work from the failed node. Enterprise Edition also introduced the Addressing Windows Extensions (AWE), which enables Windows to reserve only 1GB of the system RAM for itself, leaving 3GB free for applications. Applications such as Microsoft SQL Server take advantage of the additional RAM and offer better performance.
Windows Server 2003, Enterprise Edition corresponds to Windows NT Server 4.0 Enterprise Edition, providing the same clustering capabilities and memory support. In Windows Server 2003, WLBS is renamed Network Load Balancing (NLB). And, unlike Windows NT, NLB is included in all editions of Windows Server 2003, not just Enterprise Server.
Windows NT Server 4.0 Enterprise Edition also introduced a number of advanced features, such as the Microsoft Message Queue Server (MSMQ), which is present as Message Queuing Services in all editions of Windows Server 2003.
Windows Server 2003, Datacenter Edition is an extension of Windows Server 2003, Enterprise Edition, and there's no directly corresponding version of Windows NT. Similarly, Windows Server 2003, Web Edition is a special-purpose version of Windows Server 2003 and doesn't correspond with a specific edition of Windows NT. Windows NT Server 4.0 Terminal Server Edition doesn't correspond to any version of Windows Server 2003 because all editions of Windows Server 2003 include Terminal Services capabilities.
If you're performing an upgrade from Windows NT 4.0 to Windows Server 2003, you'll need to upgrade with a corresponding edition of the operating system:
Upgrade Windows NT Server 4.0 computers by using Windows Server 2003, Standard Edition.
Use Windows Server 2003, Enterprise Edition to upgrade Windows NT Server 4.0 Enterprise Edition.
Windows NT Server 4.0 Terminal Server Edition can be upgraded by using either Windows Server 2003, Standard Edition or Enterprise Edition; Standard Edition is the most common choice.
Note that Microsoft doesn't provide an upgrade path from any NT operating system to Windows Server 2003, Datacenter Edition; almost by definition, any hardware running NT 4.0 won't be compatible with Datacenter Edition.