At a more conceptual level, Datacenter supports two types of scalability: a Windows-centric scale-out model and the more UNIX-like scale-up model. In the scale-out model, capacity is added by adding more servers to the mix, and Datacenter supports this feature through NLB and Server Clustering. In the UNIX-like scale-up model, however, a single server gains capacity by adding more hardware resources, such as RAM, hard drives, and microprocessors. Datacenter implements scale-up through its support of 32-processors and 64 GB of RAM in a single system. But because Datacenter supports both modes, it offers customers a choice when it comes to adding capacity. Previously, this choice required a decision between Windows and UNIX platforms. Of course, for scalability to be as near linear as possible, the underlying software needs to be designed, configured, and tuned correctly. Microsoft says that Datacenter achieves this balance. Other Microsoft Server products--such as SQL Server 2000--are now offering this dual mode scaling as well.
Unique features in Datacenter
But it is Datacenter's unique features that really set it apart from other members of the Windows 2000 Server family. These features include Physical Address Extension (PAE) support, which allows Datacenter to access vast amounts of RAM; Winsock Direct for fast SAN networking; a Process Control tool for management of processes and new job objects; hardware partitioning for multiple instances of the OS on a single server; and a Windows Datacenter Program that ensures that Datacenter-compatible hardware is of the highest quality.
Microsoft provides support for Physical Address Extension (PAE), a component of the Enterprise Memory Architecture (EMA) that makes it possible to access memory above 4 GB on 32-bit Intel-based systems (Pentium Pro or later). EMA is designed to let applications access vast amounts of RAM efficiently, which adds dramatically to the performance of Windows 2000 AS and Datacenter-based systems that can take advantage of this technology. In AS, two EMA technologies are employed, a 4 GB Tuning (4GT) featuring and PAE, which allows the system to access up to 8 GB of RAM. But in Datacenter, this limit is raised to 64 GB. Such systems exhibit very little disk paging, providing applications with the fastest possible environment because the OS and applications can exist entirely in RAM. But the best news is that supporting EMA requires the mastery of only four new system calls. The AWE Application Programming Interface (API) provides applications with a way to access RAM above 4 GB inside of a memory window that harkens somewhat to the dark days of 16-bit Windows 3.x segment-based programming.
Indeed, supporting large memory situations will be somewhat cumbersome until Windows 2000/64 (the 64-bit version of Windows) and Intel's Itanium--with its correspondingly huge memory environment--are widely available. In a Windows 2000 Server system, for example, 4 GB is the upper limit, and there's no way to configure the system to use RAM more efficiently for running applications. Instead, 2 GB is reserved for the OS and 2 GB is put aside for applications. In AS, things get a little more interesting: 1 GB of the RAM normally reserved for the OS can be set aside applications, giving them access to up to 3 GB of RAM. To access the full 8 GB in AS, applications will need to program to the AWE API and ensure that AS is running with the PAE-enabled kernel. This will provide applications with up to 7 GB of space on AS. In Datacenter, the theory is similar, but the payoff is much bigger because Datacenter can access so much RAM.
Another major advantage of Datacenter is Winsock Direct, which provides standard Winsock applications with the capabilities they need work on high-speed System Area Networks (SAN). Winsock--or Windows Sockets--is a programming interface that lets TCP/IP-based applications such as Internet Explorer run under Windows. Winsock Direct is an extension of Winsock that makes SAN networking as transparent as standard LAN-based networking, while providing the types of speeds we've come to expect from a LAN. SANs are similar to LANs, but they are physically secure and offer higher bandwidth and lower latency than traditional LANs. And because reliability features are built directly into SAN hardware, packets are virtually guaranteed to route correctly and efficiently. Before Winsock Direct, most SAN application programming required an understanding of proprietary transport technology, because most SANs don't use TCP/IP. But Winsock Direct allows the wide range of available TCP/IP applications to run unmodified over SANs. And TCP/IP doesn't even need to be installed for this feature to work.
Datacenter also includes a feature, called Process Control, that simplifies the management of server resources. Process Control is an MMC-based tool and command line utility that gives administrators the ability to finely control resources so that particular applications can be assigned specific resources. It works with a Datacenter-specific kernel object called a Job object, which is used to collect one or more server processes into a single, named unit. Job objects have numerous capabilities, and administrators can create rules in Process Control that expose these capabilities. For example, you might create a rule that prevents an application from using too much RAM or processor time. Process Control can be used for a variety of related tasks, including assigning scheduling priority to processes or process groups, enforcing processor and memory limits for processes, and the like.
Windows 2000 Datacenter supports an interesting feature called hardware partitioning, which makes it possible to run multiple copies of Datacenter on the same physical server. While hardware partitioning won't make sense for any but the most powerful of servers, Datacenter will be the first Microsoft OS to offer this capability. Microsoft SQL Server 2000 offers a similar feature that makes it possible to install more than one copy of the database server on a single system.
Datacenter Licensing
Datacenter is changing the rules when it comes to licensing as well. Datacenter will not be sold at retail but will instead be offered only through qualified PC makers who can offer three basic licensing options: up to eight processors, up to 16 processors, or up to 32 processors. The 16 and 32 processor licenses can be upgraded as needed. To qualify for a Datacenter license, a server must offer at least 8-processor capability. This doesn't mean that the system must ship with 8 processors, but it must support at least eight out of the box. So it's possible, for example to ship a single processor Datacenter system, though such servers will likely be rare. Datacenter doesn't ship with any Client Access Licenses (CAL), so these must be purchased separately.
PC makers will also be able to offer Datacenter with an updateable yearly subscription license, which gives customers access to yearly version releases, supplements, and Datacenter-specific service packs. Customers that purchase the subscription license may later opt not to update it, but they will then lose the ability to gain access to the latest product updates. And customers that do not purchase a subscription license can later update to the subscription and immediately gain the benefits of a subscription license if desired.
Windows Datacenter Program
But it's arguable that the most important feature of Datacenter isn't even part of the OS: To offer customers an end-to-end solution comprising hardware, software, and support, Microsoft has joined with its first-tier hardware partners to create the Windows Datacenter Program (WDP). The WDP requires that Datacenter is only obtained when loaded onto a server that's built by one of these PC makers. So customers won't be able to purchase Datacenter at retail and install it on homebrew hardware. Instead, Datacenter will be bundled only with that hardware that has passed Microsoft's rigorous testing and certification process, giving customers a guaranteed, highly reliable solution. So the WDP provides a single entry point for support and service, ending confusion about which solutions supplier is required to support the customer.
Microsoft has also created the Windows Hardware Quality Labs (HQL) so that hardware and software makers can ensure that their products work with Datacenter and other versions of Windows 2000. Hardware products that pass the corresponding Hardware Compatibility Test (HCT) are placed on the Datacenter Hardware Compatibility List (HCL), an exclusive subset of the wider Windows 2000 HCL. The Datacenter HCL provides customers with a concise list of the hardware that is guaranteed to work with Datacenter. And of course, hardware that isn't on the HCL can't be sold in a Datacenter system: PC makers must also ensure that all hardware drivers, kernel level software, virus software, disk and tape management software, backup software, and the like be certified for Datacenter, resulting in highly dependable Datacenter systems.
Specific vendor systems that pass these rigorous tests will be placed on the HCL as well, a scheme Microsoft previously used for clustered NT 4.0 and Win2K systems. But PC makers that make the cut are required to maintain Datacenter-compatible systems that meet the WDP requirements for the life of the current version of Datacenter plus 18 months, ensuring a support system for customers. WDP PC makers must offer a variety of services to these customers, including full installation of the OS and all drivers, an evaluation of Datacenter in the customer's environment, onsite service with company employees or subcontracted through a third party, and more. Datacenter systems must meet a minimum uptime guarantee of 99.9%, with clustered systems offering even higher uptimes.