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The UNIX Operating System CHAPTER1 6728_shah_01_cc.qxd 4/13/00 12:19 PM Page 1 PARTONE Know Your NT System 6728_shah_01_cc.qxd 4/13/00 12:19 PM Page 2 6728_shah_01_cc.qxd 4/13/00 12:19 PM Page 3 CHAPTER1 The UNIX Operating System nd on the 6.9th day, He created UNIX. Before we jump onto the trampoline of delights that is the process of A integrating UNIX and Windows 2000, we first need a stable position to jump from. In this respect, we begin by a succinct introduction to UNIX. It’s not that we don’t think you already know all there is to know about it, but we want to give comparable concepts between the two operating systems, so that when we begin talking about Windows 2000, you will understand what we mean. This isn’t an utter, complete, comprehensive, all-encompassing, every- bit-about-everything review of UNIX, only most of the basic ideas on how the system works and runs. It tries not to go too much into the pro- gramming depths of the operating system (OS), but then if you were interested in that, you’d be reading a hardcore book on the internals of UNIX instead. It also cannot cover every tool and command that is avail- able in UNIX across all the versions because of the years of variations between them. What’s more, we expect that you may have a bit of expe- rience with UNIX as it is. What this book will give you is a working understanding of how UNIX runs so that you can compare it against the Windows 2000 architecture. 3 6728_shah_01_cc.qxd 4/13/00 12:19 PM Page 4 4 UNIX AND WINDOWS 2000 INTEGRATION TOOLKIT UNIX Alive! UNIX is undoubtedly one of the most resilient operating systems ever. It is also the only operating system still in wide commercial use that’s almost 30 years old. It has evolved over the years to take advantage of new ideas in computer science as well as new hardware technology. Yet, there are ideas and concepts in UNIX that its progenitors could point to and see similarities in since its first inception. Today, UNIX can be seen running in the largest massively parallel computers in the world, as well as some of the smallest handheld devices. What we really see is not one operating system but a whole family of them, running on different processor types and system motherboards, and with different capabili- ties. And all it took to start the whole shebang was one idle programmer who wanted to play a game of Space Travel. UNIX Operating System Layers The UNIX operating system is layered like most others and was one of the first to introduce a separation between the kernel and the user space (see Figure 1.1). Essentially, the model is like a cross-section of a peanut. At the very center is the kernel, which constitutes the core components of Shell scripts User-mode system applications All user applications (shells, X Windows, (login, syslog, NFS, init, inetd, etc.) editors, games, developer tools, etc.) Standard System Libraries Shared or dynamically User space loadable Libraries Network Memory Processes and File system I/O processing protocols and Kernel space management threads communications Block and character device driver interfaces, STREAMS driver interface Device drivers Hardware Figure 1.1 The UNIX operating system layers, generalized. 6728_shah_01_cc.qxd 4/13/00 12:19 PM Page 5 The UNIX Operating System 5 UNIX in Retrovision In the summer of 1969 when Ken Thompson’s wife was away for vacation at her parents’ place, he sat down to build a toy on a Digital Equipment Corporation PDP-7. He had been working on the large computer development effort at Bell Labs known as the Multiplexed Information and Computing Service (MULTICS), which had recently been put to bed as a misadvised technical nightmare. But thankfully, our hero found better use of his time, working on his own pet operating systems project, known amusingly as UNICS. Soon others at Bell Labs, like Dennis Ritchie, who thought it a surprisingly impressive toy, joined in the project and began expanding it and bringing it to more modern machines like the PDP-11 series, and in the process created another little gem known as the C programming language. In 1974, when Thompson and Ritchie published their paper on UNIX in the pro- fessional journal Communications of the ACM, they received a great deal of attention from universities across the United States that also had PDP-11 series computers. AT&T soon licensed copies of this new OS to most of them for a fee. The first standard version came out as UNIX V6, named after the sixth edition of the UNIX Programmer’s Manual. This is where it begins to break up. The popularity was so overwhelming that several academic groups decided to enhance it with their own versions. The first two derivatives were XENIX and BSD. The former eventually went on to become SCO UNIX, and the latter can still be seen in FreeBSD, NetBSD, and all its derivatives. The University of California at Berkeley was primarily responsible for the Berkeley Systems Design (BSD) version. Other UNIX legendaries like Bill Joy, Kirk McKusick, and Rob Kolstad joined the BSD group over time to develop several versions. The BSD group also was the first introduce the TCP/IP protocol into UNIX, and created the standard communications model known as sockets. For the longest time this had stabilized into version 4.2 and then 4.3, and several compa- nies licensed this code to make their own operating systems, including Digital Ultrix and Sun Microsystems’ SunOS. On the commercial front, AT&T still owned the license and continued to develop its version of the standard, which split off after Version 8 and rejoined with several of the other UNIX efforts to eventually become System V Release 3. The last improvement to this was released as UNIX System Version 4. Today, com- mercial and noncommercial UNIX operating systems such as Sun Solaris, SGI IRIX, IBM AIX, Compaq Tru64 UNIX, SCO UnixWare, FreeBSD, and NetBSD are actually a combination of features from both these lineages. There have been attempts to merge or submerge the various different versions of UNIX, but pretty much through and through both BSD and System V have continues 6728_shah_01_cc.qxd 4/13/00 12:19 PM Page 6 6 UNIX AND WINDOWS 2000 INTEGRATION TOOLKIT UNIX in Retrovision (Continued) survived to the end. Most commercial UNIX from large vendors is still based on the System V model, although there have been so many changes, everyone has given up the pretense that they are compatible. Development now continues along the lines of each of these products through their respective vendors and developer communities, although there continue to be private individuals and groups working on the next best UNIX. The official UNIX standard is now in the hands of the Open Group (www .opengroup.org), an independent nonprofit organization. It was sold by AT&T to No- vell in the early 1990s, then by Novell to SCO, and then was handed over to the group. SCO’s UnixWare (formerly Novell’s and AT&T’s) is closest in specification to the official UNIX 98 standard, but then again, the standard is mostly a list of supported APIs and command tools. You want to know something really bizarre? By the definition and product testing of the Open Group, a number of other operating system platforms can also legally be called UNIX, including the IBM OS/390 running on mainframes (the same ones UNIX fought against decades ago) and another product called Interix from Softway Systems that—get this—actually runs on top of Windows NT! In any case, independent development of UNIXlike platforms never ceases. One famous example today is Linux. Back in 1991, a Finnish developer decided to put his free time into making a completely new version of UNIX, which borrowed the ideas but not the code and intellectual property of UNIX. Soon, Linus Torsvald and his friends combined their efforts with others across the Internet to build on this version, called Linux. It was picked up by enthusiasts everywhere, and today there are an estimated 7 million Linux users. A number of companies offer differ- ent distributions of Linux for sale for the packaging, not the actual OS itself. In recent years, Linux has become the best-selling OS from the UNIX-like group of operating systems, and continues to be so because of its model of open source contribution in which anyone is allowed to see, modify, and release versions of the operating system without any need for a license fee. The fact that it has a free license makes it very appealing to individuals and companies alike. Development of Linux is still controlled by Linus and his core developers, but most releases come packaged from organizations such as Red Hat, Debian, Caldera, SuSE, and TurboLinux. the operating system. Wrapped around this are other layers, which build up the applications and tools, and covered at the very outside is the shell, the environment that the users interact with. Although the original OS model was a monolithic design in which all kernel operations were combined together into the same 6728_shah_01_cc.qxd 4/13/00 12:19 PM Page 7 The UNIX Operating System 7 executive, today there are microkernel versions of the operating system as well, separating each component, such as memory management, file systems, input/output (I/O) processing, and so forth, into separately loadable kernel components.
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