Internet Information Server (IIS) and More

Microsoft has included its Internet Information Server (IIS) with NT Server to make it easy for you to connect your organization to the Internet, or to create an Intranet to browse your organization's internal resources. You have the option of installing IIS 2.0 when you are installing NT Server or any time thereafter. What is unique about the Internet Information Server is that it is free. This may be an effort to convince business that IIS could be used to as a low cost (or no cost) alternative to the other Web servers on the market today. Microsoft hopes that you will see the value in their Web server and begin using it. However, IIS will not run on anything other than Windows NT, so you must have an NT Server in order to take advantage of IIS.. In addition to providing the basic features of IIS, Microsoft offers additional BackOffice products to enhance its functionality. Microsoft Proxy Server is for connecting your network to the Internet. Microsoft SQL Server for connecting databases to IIS for viewing and updating information in the database over the network or Internet. You can also read your e-mail through a Web browser with Exchange Server. These are just a few of the possibilities that exist with IIS.. Since the popularity of both NT Server and the BackOffice suite have greatly increased, we urge you to become certified in these products. By becoming certified, you demonstrate your ability to support the IIS and the various products that take advantage of it.The following sections describe the features that are part of the IIS and explain theservices they provide for NT Server.

Index Server

The Index Server, provided with IIS, enables you to index all HTML documents and other supported formats. It has the ability to find text in HTML documents, as well as Word, Excel and various other text documents. When you have indexed all of your data, you can query that data using keywords to bring up documents that contain the desired information.. This is just like using an Internet search engine to find what you are looking for.(Quite possibly the search engines are also using Index Server to index information.) Once you tell Index Server what information to index, it performs the tasks; it also continues to index new documents as they are added to the server.

FTP Server

You can use the File Transfer Protocol (FTP) server to upload or download information within your company, or outside your company via the Internet. Having an FTP site is useful when outside sources need to send or receive information that is too large to be attached to e-mail. Many organizations provide FTP services along with Web services for making software updates, patches, and drivers available to the public. Although FTP is slowly becoming replaced by the Web, it is by no means dead. FTP still has widespread acceptance in the Internet community, even though it is not as user-friendly as the Web.

Gopher Server

A Gopher server is included with IIS, although the popularity of the World Wide Web has made Gopher nearly extinct. Gopher can be used as an index to look for information on the Internet, or on your own company's Intranet. You can use menus to access text files that are available on the Internet. Gopher is easy to use, has the ability to create links to other computers, and enables you to make your own menus.

Administrative Wizards

NT 4.0 Server includes a number of Administrative Wizards that help you perform common administrative tasks. They do not contain any added functionality—they simply guide those unfamiliar with NT 4.0 Server through the basic operations. After you are comfortable with the Administrative Wizards, you should be ready to venture out on your own. Eight Administrative Wizards are currently available:

Windows NT Architecture

Windows NT architecture is unlike any other operating system in Microsoft’s arsenal. Many of Microsoft’s operating systems—such as MS-DOS or Windows 3.x— require DOS; some argue that Windows 95 stills needs DOS. However, NT has no DOS code at all. This is amazing when you consider that NT can still run DOS and older Windows 16-bit applications. Not only can it run these programs, but in some cases they will run better than in their native environment! If you have been using NT Server since the first version, you may not have seen drastic changes to the architecture with each new version, but NT 4.0 is significantly different from other operating systems. The next sections will describe the architecture that makes NT unique.

User Mode versus Kernel Mode

An important feature of Windows NT, and one that contributes to the great stability of its architecture, is the use of two types of operating mode. The two modes, User mode and Kernel mode, differ primarily in the amount of privilege assigned to each. User mode cannot directly access the hardware, whereas Kernel mode can. Figure 1-1 is an overview of the NT architecture, showing the role of User mode and Kernel mode.

User Mode

User mode, often referred to as non-privileged processor mode, is where most of Windows NT code is located. This is also where applications and the various subsystems are run. This mode cannot communicate directly with the hardware, and must call upon the operating system to make these calls. This provides stability for the operating system by creating a protective barrier from misbehaving applications, which could possibly bring down the entire operating system.

Kernel Mode

Kernel mode—commonly referred to as privileged mode—does have direct access to hardware and software resources in the system. Applications that require hardware functions must be translated into these Kernel mode instructions. The Kernel mode must translate the calls from User mode before the hardware can be accessed, and then must pass the data back to User mode. An important note about the release of NT 4.0 is the fact that some components of NT that used to run as User mode components now run as Kernel mode components. These include the Window Manager, the graphical device interface (GDI), and graphics device drivers. With these components running in Kernel mode, there should be an increase in graphics performance because you no longer need to translate the calls back and forth between the two modes.

Hardware Abstraction Layer (HAL)

The User-mode applications never call the hardware directly, because these calls are handled by the Windows NT Executive. Similarly, the Hardware Abstraction Layer (HAL) separates the kernel from the hardware to provide an intermediary layer so that the Windows NT kernel does not have to communicate with the hardware. The HAL is the most common reason why some DOS and early Windows applications are incompatible with NT. These applications expect to communicate directly with the hardware, and will not run if they are not given this privilege. Although this appears to be a disadvantage,, it is actually an advantage because the HAL provides increased protection from errant applications. However, the HAL increases system complexity. Not only do you need a separate HAL for each hardware platform, but you need two HALs for each processor architecture—one to support a single processor, and another to support multiple processors.

Windows NT Microkernel

The term microkernel, or kernel, refers to the core of code in an operating system. This is the most important part of the operating system and is responsible for all functions on the system. However, the kernel cannot do this all by itself. It requires some other components to be responsible for their own functions, leaving the most important tasks to the kernel. As an analogy, think of the CEO of a company. The CEO does not have be a part of every decision that is made at the company, but instead relies on other people such as the President, Vice-President, and various managers of the company. However, when a decision has to be made that will affect the entire company, it is escalated to the CEO, who takes all of the information gathered by the Executives and uses that information to make an appropriate decision. In Windows NT, the operating system kernel calls upon the services of the Windows NT Executive, just as the CEO called upon the corporate executives to provide critical information. NT's modular architecture allows portions of the operating system to be rewritten or replaced as needed. It also facilitates the integration of new components into the architecture.

Executive Services

The NT Executive Services (also called System Services) provide the operating system services that the kernel is too busy to perform. The kernel is actually part of the NT Executive, and together they are responsible for the entire system. The NT Executive includes the following operating system components:

Figure 1-2 summarizes the Executive Services of Windows NT 4.0.

Windows NT Subsystems

Windows NT maintains compatibility with existing applications through the use of an environment subsystem that mimics the environment that the application expects to see. Figure 1-3 illustrates some examples of environment subsystems. If a subsystem for a specific environment were not included in the operating system, there would be no backwards compatibility with non-NT applications using that environment. Subsystems for some of the infrequently used environments, such as POSIX and OS/2, can be loaded as needed. This saves memory because they need not be loaded at system startup. However, the Win32 primary subsystem is always created at startup.

Notice that these services are referred to as "subsystems" because they can perform independently of any other subsystem. These subsystems run completely in User mode and each is isolated from other subsystems; this is why they are sometimes referred to as "protected" subsystems.

Win32

As shown in Figure 1-3, Win32 is the primary subsystem for NT, and it is responsible for all user input and output. The Win32 subsystem is also responsible for receiving requests from the other environment subsystems. Win32 used to have the GDI and USER components in the Win32 subsystem, but they have been moved to the NT Executive in the release of NT 4.0. Two subsystems, MS-DOS and Win16, actually belong to the Win32 subsystem. The Win32 subsystem provides a 32-bit, preemptively multitasked environment, where each application receives its own address space for greater stability.

MS-DOS

The MS-DOS subsystem is quite possibly the most important subsystem in NT for compatibility. The DOS environment is called the virtual DOS machine (VDM). The VDM fools the DOS application into thinking it is the only application running, just as it was run in the DOS operating system. The VDM is a 32-bit application run in a separate memory space that is capable of being multitasked with other applications (thereby increasing performance). This subsystem will run DOS applications, but it will also run Windows applications that require DOS.

Win16

Since 16-bit Windows applications run over DOS, they must be emulated in this way to work with Windows NT. This is achieved by running the VDM and an emulator called the WOW— short for Win16 on Win32. When a 16-bit application is run, it will have to have the Win16 calls translated into Win32 calls, or vice versa. This is done by a process known as thunking. It is much easier to make the Win16 call to Win32 because you just have to add bits, whereas it is much more difficult to go from Win32 to Win16 because you cannot just drop bits.

For 16-bit applications that expect to share address space with other 16-bit applications, the applications are run in a single VDM. Although the 16-bit Windows applications are run in the same memory space by default, they do have the option of being run in a separate memory space. If the applications are run in a shared memory space, there is an increased possibility that one faulty 16-bit application will bring down every application that is sharing the memory space. When the applications are run in their own separate memory space, any application that crashes only affects itself— not other applications currently running outside of the memory space. This is a welcome feature for users of many older 16-bit applications that had trouble with misbehaving applications in the past.

OS/2 Subsystem

The OS/2 subsystem is the most limited of the subsystems provided with NT. There is less need to create a fully functional OS/2 subsystem because support for the OS/2 environment has dwindled. Although the OS/2 subsystem is a 32-bit, multitasking protected subsystem, it can only run character-mode applications; it cannot run graphical applications. Interestingly enough, the OS/2 interface was going to be the primary subsystem for NT until the surprising popularity of the Windows 3.1 operating system. This made the Win32 primary subsystem a more logical choice.

POSIX Subsystem

The POSIX subsystem is included to support open standards, mostly for application support for UNIX platforms. In order to be POSIX-compliant, the software must fulfill certain requirements, such as case-sensitive filenames, hard links (which can be compared to Windows NT shortcuts, in which many entries can point to the same file), and additional time stamping. The POSIX subsystem is a 32-bit, multitasked, protected subsystem; however, you will not have many opportunities to take advantage of it because of the lack of support.

Windows NT Memory Organization

The memory organization of Windows NT is built around three main concepts: virtual memory, demand paging, and a 32-bit flat address space. Each of these methods helps Windows NT provide memory for applications, even when the amount of physical memory has been exceeded.

Virtual Memory

Windows NT uses virtual memory to simulate RAM on a computer when more memory is needed. It does this by using the computer's hard disk as needed. Figure 1-4 illustrates how data can be moved from RAM to hard disk. When the computer is not using a portion of data in RAM, the data can be swapped in 4K pages to the hard disk and replaced with data that is currently needed.

Of course, RAM operates much faster than the hard drive, so virtual memory is no substitute for having enough RAM in your system. In older operating systems such as DOS, when you did not have the luxury of virtual memory, the application would not run at all. To accomplish this process, a component of the Windows NT Executive called the Virtual Memory Manager (VMM) is used. The VMM is responsible for mapping the virtual addresses to the physical pages of computer memory. The VMM is also responsible for the actual paging process, which will be described later in this book.

Demand Paging

Demand paging is the process of swapping the information from disk or memory in 4k pages as needed. This process requires the use of the NT paging file, which is an actual file on your hard disk reserved for this use. If your paging file is not large enough, you will see error messages that your system is running low on virtual memory. You will learn more about configuring the paging file in later chapters of the book. For now, you just need to understand that the hard disk will be used when your physical memory is exceeded. You can tell that the hard drive is being used for paging when you hear the hard drive make noise as you switch to another open application If you had enough RAM, the switch would be instantaneous. Try opening several applications and switching among them to see when your system begins using the page file. You can also bring up the Windows NT Task Manager and view the available physical memory from the Performance tab.

Another term to keep in mind is thrashing. Thrashing sounds much worse than paging, and it is. When you have exceeded the amount of physical RAM in the system, and your paging file is becoming full, the system will begin thrashing to look for more available memory. This is a not good for the system, and you should take corrective action, such as adding more physical memory or increasing the size of your paging file.

Linear 32-bit Address

Applications use a 32-bit linear address when they access memory. This is different from the segmented scheme used for MS-DOS and other versions of Windows. With the segmented memory scheme, an application accesses memory by using a segment and an offset; the combination of these two coordinates can identify a memory address. It is comparable to a grid which has rows and columns. To find a location on the grid you find the appropriate row (the segment), then find where it intersects with the column (the offset). The computer required extra time to compute location using this segmented memory scheme; ittook even more time for software developers to use this method, because it was difficult and slow.

With the linear 32-bit address, the first address starts at zero, and continues in one-byte increments until the system is out of physical memory. Since memory allocated in this way must use unique addresses, a 32-bit address gives you 4 GB of address space. Two gigabytes of this address space is reserved for the applications to use, and the other 2 GB is reserved for the system's use. This linear addressing makes NT more compatible with different processor architectures because more RISC processors (and even some CISC processors from Intel) use linear addressing.

Device Drivers

Device drivers enable your system to communicate with the various devices in your system. A driver is basically a small application that the operating system calls when it needs the device to perform a function. A well written driver is important for the stability and performance of your system. A wrong or poorly written device driver will not maximize your performance, and it may cause system problems or just not work at all with the device. Since the driver must communicate with the device to perform a function, you can see how important it is to make sure you have the correct version of the driver. Older drivers for Windows 3.x or Windows 95 will not work with NT, and previous NT versions of drivers may not work either. Microsoft has provided many compatible drivers for use with the operating system, but may not have current drivers for brand new devices. The device vendors may also provide new drivers for NT 4.0 on their Internet Web sites. The good news is that drivers are continually updated. The bad news is that there are still not that many available for NT.

Certification Summary

Windows NT Server was created as a high performance network operating system that is optimized for resource sharing. This chapter described the features that increase performance such as preemptive multitasking of applications and the how processes spawn threads of differing priority. Priority of these threads is inherited from the parent process, but can be adjusted. Not only can you multitask applications, you can add more processors to the NT system to take advantage of multiprocessing. This allows threads to run on any processor in the system. Fault tolerance is supported by the use of hot fixing, the use of Backup Domain Controllers, multiple network cards, directory replication, and RAID support. The Redundant Array of Inexpensive Disks offers varying levels of performance and fault tolerance, of which NT supports levels 0, 1, and 5. Levels 1 and 5 are mirroring and disk striping with parity respectively. These are both capable of withstanding hard disk failure.

Integrated with Windows NT Server is the Internet Information Server (IIS). This Web server allows you to run your own Web page on the Internet or your company's Intranet. IIS comes with Index Server, and both FTP and Gopher servers.

Under Windows NT architecture, the chapter covered the two modes that portions of code and applications are run in: User mode and Kernel mode. Kernel mode has direct access to the system resources whereas User mode does not. The Hardware Abstraction Layer (HAL) is used as an intermediary between the hardware so the NT kernel does not have to communicate directly with the hardware. The kernel is the core of the operating system, and the head of the NT Executive Services. The kernel and the Executive Services are responsible for the entire system. Windows NT maintains compatibility with existing applications through the use of an environment subsystem that mimics the environment the application expects to see. Examples of environment subsystems are the POSIX, OS/2, and Win32 subsystems. The DOS and Win16 subsystems are actually housed within the Win32 subsystem. Since the DOS and Win16 subsystems are a part of the Win32 subsystem, they also run in User mode. They are also preemptively multitasked with other applications on the system, and protected from each other. They both need to call upon the Win32 subsystem, which is the primary subsystem that handles these requests in NT.

The memory organization of Windows NT is built around three main concepts: virtual memory, demand paging, and a 32-bit flat address space. Virtual memory uses the hard drive to simulate RAM as needed. Demand paging is the process of swapping pages of memory between the hard disk and memory. The 32-bit flat addressing scheme is an improvement over the segmented memory method. The 32-bit scheme, which allocates addresses in one-byte increments until the physical memory is all gone, allows for 4 GB of virtual memory.

Two-Minute Drill