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Local Procedure Call Facility

Programs that execute under Windows NT have a client/server relationship with the operating system. The Local Procedure Call Facility is responsible for the passing of messages between programs.


Exhibit 2.  Virtual Memory Dialog Box.

I/O Manager

The Input/Output (I/O) Manager is responsible for managing all input and output to and from storage and the network. To perform its required functions, the I/O Manager uses four other lower-level subsystems — the Cache Manager, file system drivers, hardware device drivers, and network drivers.

The Cache Manager provides a dynamic cache space in RAM that increases and decreases based on available memory. File system drivers provide support for two file systems, the file allocation table (FAT) and the high performance file system (HPFS). The FAT file system provides backward support for DOS and 16-bit Windows 3.X-based programs, whereas the HPFS enables support of the new file system for Windows NT 32-bit applications.

The hardware device drivers used in Windows NT are written in C++ to provide portability between hardware platforms. This allows a driver developed for a CD-ROM, a plotter, or another hardware device to work with all Windows NT hardware platforms.

Network drivers represent the fourth lower-level I/O Manager subsystem. These drivers provide access from Windows NT to network interface cards, enabling transmission to and from the network and the operating system.

The Security Module

Windows NT includes a comprehensive security facility built into the operating system. Once the user turns on power to the hardware platform, this facility is immediately recognizable. Unlike Windows 3.X, Windows 95, or DOS, Windows NT prompts the operator for a password before allowing access to the computer’s resources.

Windows NT security works by the log-on process and a local security subsystem that monitors access to all objects and verifies that a user has appropriate permission before allowing access to an object. The log-on process is linked to the Security Reference Monitor, which is responsible for access validation and audit generation for the local security subsystem. Another component of the Security Module is the Security Account Manager. The Security Account Manager maintains user and group information on a secure database.

WINDOWS NT NETWORKING

One of the biggest advantages associated with the use of Windows NT is its built-in support of many transport protocols. The Windows NT networking architecture was established in a layered design that follows the seven-layer ISO Open System Interconnection (OSI) Reference Model. Exhibit 3 illustrates the general correspondence between Windows NT layers and OSI Reference Model layers.

The environment subsystems represent virtual DOS machines as well as 32-bit applications operating on top of NT. At the presentation layer, the Network Provider module is required for each network supported through a redirector. At the session layer, the Windows NT Executive uses a server and redirector to provide capability for a server and workstation, respectively. Both components are implemented as file system drivers and multiple redirectors can be loaded at the same time, so that a Windows NT computer can be connected to several networks. For example, NT includes redirectors for NetWare and VINES, enabling an NT workstation or server to be connected to Novell and Banyan networks.

Exhibit 3. Correspondence Between Windows NT and OSI Reference Model Layers
OSI Reference Model Layers Windows NT Layers
Application Environment Subsystems
Presentation Network Provider
Session Executive Services
  Server Redirector
Transport Transport Driver Interface
Network NetBEUI DLC TCP/IP NSLink (SPX/IPX)
Data Link NDIS
  NIC Drivers
Physical NIC

At the transport layer, the transport driver interface (TDI) provides a higher-layer interface to multiple transport protocols. Those protocols, which represent operations at the network layer, include built-in NT protocol stacks for NetBEUI, used by the LAN Manager and LAN Server operating systems; Data Link Control (DLC), which provides access to IBM mainframes; TCP/IP for Internet and intranet applications; and NWLink, which represents a version of Novell’s SPX/IPX protocols. Through the use of TCP/IP, a Windows NT computer can function as a TCP/IP client, whereas the use of NWLink enables a Windows NT computer to operate as NetWare client.

At the data link layer, Windows NT includes a built-in Network Device Interface Specification (NDIS). NDIS enables support for multiple protocol stacks through network interface card drivers. Thus, NDIS allows a network interface card to simultaneously communicate with multiple supported protocol stacks. This means that a Windows NT computer could, for example, simultaneously operate as both a TCP/IP and a NetWare SPX/IPX client.

UPGRADE ISSUES

The key differences between NT 3.5 and 4.0 are speed and user interface. Windows 4.0 added the Windows 95 user interface to NT. In addition, a recoding of the operating system makes it slightly faster than 3.51. However, because the difference in cost between a Pentium and Pentium Pro microprocessor is a few hundred dollars, it may be more economical to purchase the more powerful processor and retain the familiar Windows 3.51 interface. This could eliminate the costs associated with retraining employees.

Conversely, if an organization has already migrated to Windows 95 or is planning to migrate to that operating system, the network manager may want to consider Windows NT Version 4.0. Its use of the Windows 95 interface may be well known to some or most of the organization’s employees who will be using NT, which should minimize training costs while providing a slightly improved level of performance.

CONCLUSION

The modular design of the Windows NT architecture makes it both portable and scalable. Windows NT’s hardware abstraction layer allows the operating system to run on different hardware platforms. Currently, Windows NT runs on Intel X86 and Digital Equipment Corp. (DEC) Alpha. Until the new release of NT this operating system supported the MIPS RISC (reduced instruction set computing), and the PowerPC series of microprocessors jointly manufactured by IBM Corp. and Motorola.

Besides being highly portable, Windows NT supports scalability, which allows the operating system to effectively use multiple processors. Thus, when network managers evaluate Windows NT Server as a platform for different applications, it is important for them to note that they have several options for retaining their investment as applications grow.

For example, because of its scalability, network managers could replace a uniprocessor Intel Pentium motherboard with a dual- or quad-processor motherboard. If this replacement does not provide the necessary level of processing power, network managers might consider migrating hardware to a high-level DEC Alpha-based computer. If that migration is required and the applications continue to grow, network managers could use multiple processors to ensure scalability.


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