Sams Teach Yourself MCSE Windows NT Server 4 in 14 Days
(Publisher: Macmillan Computer Publishing)
Author(s): David Schaer, et al
ISBN: 0672311283
Publication Date: 12/15/97

•  Table 2.2 compares the functions of the various roles that an NT server can play on a network.

2.2. Major NT Design Components

Windows NT has the capability to act as both a client and a server. Because a system running Windows NT can share files, it can function as a file server; because it can share print devices, it can also be a print server. Additionally, high-level applications such as Microsoft SQL Server and Microsoft Exchange Server run on the NT platform; this means NT can also be an application server.

2.2.1. The Function of the HAL

Windows NT is considered to be hardware independent. A portion of the network operating system known as the Hardware Abstraction Layer (HAL) is responsible for managing hardware. The other pieces of the network operating system communicate with HAL, which then communicates with the hardware on their behalf. This provides two very important features. It makes Windows NT independent from the actual hardware on which it runs, meaning that NT can be rapidly deployed on newer and faster processors as they are developed. Already, versions of NT are available for the Intel (CISC) and the DEC Alpha, PowerPC, and MIPS (RISC) processors.

Using HAL makes Windows NT very stable. Because no other part of Windows NT, or any application running on it, can access the hardware directly, crashes are extremely rare. When they do occur, they affect only the application or process that caused the error, and no other part of the operating system.

Early operating systems were written in assembly code, and their growth was limited to the hardware platforms for which they were designed. Microsoft overcame this by writing a majority of the NT source code in C and C++. Because these are high-level languages, the code developed can be quickly recompiled to run on other platforms. However, some of the code must be written to talk directly to the processor in the language it understands, without interpretation. This small percentage of the code is contained within a module called the Hardware Abstraction Layer (HAL).

2.2.2. Multiple Processor Support

Microsoft designed NT to take advantage of multiprocessor systems. NT Workstation 4.0 can take advantage of two processors, and NT Server 4.0 can take advantage of four processors. OEM versions of NT can reach up to 32 processors. You can easily track processor performance by using the Performance Monitor tool included with NT. In Figure 2.1 Performance Monitor is being used to track the overall percentage of processor utilization.

Figure 2.1.  You can track processor utilization by using Performance Monitor.

2.2.3. Spreading the System Code

There are two major types of multiprocessing systems: asymmetric multiprocessing (ASMP) and symmetric multiprocessing (SMP). In asymmetric processing, a processor is dedicated to the system code. In symmetric multiprocessing, the operating system can “spread” the system code across all the available processors. Microsoft has implemented the more efficient symmetric multiprocessing.

When choosing between a single, high-power, processor and a multiprocessor system it is important to consider the type of services to be provided by the server. In general, a system used primarily as a file server or print server will benefit little from multiple processors. Multiple processors often can enhance performance of application servers, such as Microsoft Exchange and Microsoft SQL Server, because they are multithreaded applications.

2.2.4. Multithreaded Applications

A multithreaded application has multiple executable entities called threads, each of which can be prioritized. For example, a word processor could have one thread to monitor the input from the user at the keyboard and another that performs spell checking. By prioritizing the thread that monitors user input higher than the thread that performs the spell checking the user never feels a response delay. The spell checker thread would receive processor time when the processor is not handling a thread of higher priority.

Because NT is both multitasking and multithreaded, several processes can pass multiple threads to the processor queue at the same time. The microkernel passes the threads to the processors based on their priority, not on their order of arrival.

The priority assigned to a process determines the priority range a thread can utilize. A normal thread within a normal priority class process is assigned a base priority of 8 on a scale of 1 to 31. By raising the priority class to high, the base priority raises to 13. Figure 2.2 shows Winword.exe as a multithreaded application (four threads) with a normal priority base.

Figure 2.2.  Winword.exe is running in normal priority with four threads.