Standard Edition
Windows Server 2003, Standard Edition is aimed towards small to medium sized businesses. Flexible and versatile, Standard Edition supports file and printer sharing, offers secure Internet connectivity, and allows centralized desktop application deployment. This edition of Windows will run on up to 4 processors with up to 4 GB RAM. 64-bit versions are also available for the AMD64 architecture and the Intel clone of that same architecture, EM64T (called, collectively, x64 by Microsoft). The 64-bit version of Windows Server 2003, Standard Edition is capable of addressing up to 32 GB of RAM and it also supports Non-Uniform Memory Access (NUMA), something the 32-bit version does not.
Enterprise Edition
Windows Server 2003, Enterprise Edition is aimed towards medium to large businesses. It is a full-function server operating system that supports up to eight processors and provides enterprise-class features such as eight-node clustering using Microsoft Cluster Server (MSCS) software and support for up to 32 GB of memory. Enterprise Edition also comes in 64-bit versions for the Itanium and x64 architectures. The 64-bit version of Windows Server 2003, Enterprise Edition [64-bit] is capable of addressing up to 1 Terabyte (1024 GB) of RAM. Both 32-bit and 64-bit versions support Non-Uniform Memory Access (NUMA). It also provides the ability to hot-add supported hardware.
Datacenter Edition
Windows Server 2003, Datacenter Edition is designed for infrastructures demanding high security and reliability. Windows Server 2003 is available for x86 32-bit, Itanium, and x64 processors. It supports a minimum of 8 processors and a maximum of 64 processors, however it is limited to 32 processors when run on 32-bit architecture. 32-bit architecture also limits memory addressability to 64GB, while the 64-bit versions support up to 512 GB. Windows Server 2003, Datacenter Edition, also allows limiting processor and memory usage on a per-application basis.
Windows Server 2003, Datacenter Edition also supports Non-Uniform Memory Access. If supported by the system, Windows, with help from the system firmware creates a Static Resource Affinity Table, that defines the NUMA topology of the system. Windows then uses this table to optimize memory accesses, and provide NUMA awareness to applications, thereby increasing the efficiency of thread scheduling and memory management.
Windows Server 2003, Datacenter edition has better support for Storage Area Networks (SAN). It features a service which uses Windows sockets to emulate TCP/IP communication over native SAN service providers, thereby allowing a SAN to be accessed over any TCP/IP channel. With this, any application that can communicate over TCP/IP can use a SAN, without any modification to the application.
Windows Server 2003, Datacenter edition, also supports 8-node clustering. Clustering increases availability and fault tolerance of server installations, by distributing and replicating the service among many servers. Windows supports clustering, with each cluster having its own dedicated storage, or all clusters connected to a common Storage Area Network (SAN), which can be running on Windows as well as non-Windows Operating systems. The SAN may be connected to other computers as well.