The UNIX System and Microsoft Windows NT Versions

Microsoft’s Windows NT operating system has been positioned as an alternative to UNIX, particularly in the server and network operating system arenas. However, it fails to equal UNIX in many areas, including adaptability, efficient use of resources, and reliability Also, as a proprietary system (unlike open-source versions of UNIX such as Linux and FreeBSD) it lacks the flexibility and readiness to incorporate new features that UNIX offers, as you will learn in this section.

Windows NT

Windows NT is a multitasking operating system designed by Microsoft to have many of the features of UNIX and other advanced capabilities not found in Microsoft Windows. Microsoft began work on NT in 1988, when it hired one of the leaders in the development of the Digital VMS operating system, David Cutler, to head this project. Windows NT was designed to compete with UNIX as the operating system for servers. Early versions of Windows NT had many problems, including a large number of bugs, poor performance, problems with memory, and a lack of application software. Release 3.5 of Windows NT eliminated many of the problems of earlier releases. Since then, many different releases of Windows NT have been introduced. In particular, Windows XP marketed by Microsoft as a desktop operating system, is really just a version of Windows NT, and was referred internally at Microsoft as Windows NT 5.1. Similarly, Windows Server 2003 is referred to internally at Microsoft as Windows NT 5.2.

Windows NT accomplished POSIX compliance using what Microsoft calls an environment subsystem. An environment subsystem is a protected subsystem of NT running in a nonprivileged processor mode that provides an application programming interface specific to an operating system. Besides the POSIX environment subsystem, Windows NT has Win32, 16-bit Windows, MS-DOS, and OS/2 environment subsystems that allow Windows, DOS, and OS/2 programs to run under Windows NT. Reviewers of NT have found many deficiencies in the Windows NT POSIX environment subsystem.

Differences Between Windows NT and UNIX

Windows NT was designed to share many of the features of UNIX, but there are many substantial differences. UNIX is a case-sensitive operating system, whereas NT often ignores case. This can cause problems, since a user may really want to have two files in the same directory that differ only by the cases of their names (such as DRA and Dra). Both Windows NT and UNIX System V are multitasking operating systems. However, Windows NT supports only one user at a time (although applications on servers may allow concurrent use by multiple users even though the operating system only deals with one user at a time), whereas the UNIX System can support many simultaneous users. There is only one Windows NT, controlled by Microsoft, but there are many versions of UNIX, but with standardization efforts, different versions of UNIX share features and interfaces. For example, both Windows NT and UNIX support a user-friendly graphical user interface. With the standardization and adoption of the CDE by essentially all UNIX vendors, the graphical user interface for UNIX is compatible across different UNIX variants.

One of the major advantages of UNIX is its capability to be adapted to new hardware. For example, Windows NT is a 32-bit or 64-bit operating system, whereas most versions of UNIX are now 64-bit operating systems, with 128-bit versions now available. This allows UNIX to support complex computing applications that require a large address space, such as applications that arise in DNA research, and to take advantage of the performance gains produced when 128-bit processors are used. There is a fundamental difference in the system design of UNIX and NT. Windows is an event-driven operating system, whereas UNIX is a process-driven operating system.

You can run Windows programs using either Windows NT or a version of UNIX with a Windows emulation package. Windows NT is only partially compliant with POSIX standards, by contrast with the most widely used variants of UNIX. Windows NT complies with the POSIX 1003.1 specification, but only within its POSIX environment subsystem. Windows applications are not POSIX compliant. On the other hand, many widely used UNIX variants are POSIX 1003.1 compliant. Unlike many versions of UNIX, Windows NT is not compliant with the POSIX.2 specification that defines command processor and command interfaces for standard applications. NT also does not comply to the POSIX.4 specification for a threads interface.

Windows NT runs on a limited set of processors. UNIX, on the other hand, runs on just about every processor in use today. Windows NT requires 12 MB of memory to run on a computer, whereas UNIX requires much less memory, with some versions requiring as little as 2 MB. One reason for this is that variants of UNIX can be run without a graphical user interface (GUI), unlike Windows.

Comparing UNIX and NT for Servers

The Microsoft Corporation has been developing Windows NT to compete head to head with UNIX for use on servers. The vast marketing effort undertaken by Microsoft has made inroads in this market, and Windows NT has become suitable for some, but not all, server applications. However, UNIX is continuing to evolve more quickly than Windows, primarily because of its openness and the large community of developers working on UNIX.

Many differences distinguish Windows NT and UNIX in the server area. UNIX is considered much more scalable than Windows NT for large applications, such as those that use extremely large databases, with systems that use as many as 128 processors. Windows NT is limited to 32 processors and two gigabytes of addressable memory on all the architectures it supports; the same is not true of UNIX. UNIX-based systems have run more than 100,000 transactions per minute.

Reliability is another important area where UNIX outshines Windows NT. Several UNIX vendors have developed sophisticated clustering capabilities that permit a large number of UNIX systems to run as a single unit. Windows NT does not support this capability for more than two systems. Load balancing across machines in a cluster is another area in which UNIX has outpaced Microsoft’s NT operating system.

Considerable cost savings can also result from the use of open-source variants of UNIX instead of Windows NT, especially when it is possible to clone servers. With Windows NT, additional costs are incurred for each server closed. Furthermore, you can obtain open-source application software for variants of UNIX, such as web server software, mail server software, database software, and integrated office software. Although analogous open-source software is also available for Windows, it often does not run as well on Windows platforms. To obtain application software of similar quality for Windows NT, you would need to spend a considerable amount of money.

How the Evolution of UNIX Differs from That of NT

Unlike UNIX, NT is not an open operating system. You cannot gain access to the source code for NT as you can for many important variants of UNIX. Source code for these variants of UNIX is readily available, either free of charge or for a fee from a vendor. NT is also a proprietary operating system, so that Microsoft controls its evolution. Some versions of UNIX are proprietary, but others are not, and no one can control the evolution of UNIX (although such people as Linus Torvalds can influence it). The openness and lack of central control makes it possible for UNIX to evolve as people develop new features, which may find their way into future versions. The only way for NT to evolve is for Microsoft to develop enhancements-and this is a severe limitation, even with the large technical staff employed by Microsoft.