The UNIX Operating System and the ' XENIX Standard Operating Environment Robert B Greenbeg XENDC Product Manager Miaosoft loa00 NE Eighth, Suite 819 Belleme WA 98004 Never has there been a greater de- ibility, and simplicity, and its vast ment from the UNIX operating mand for software that is easy to use array of software utilities greatly in- system, and how it can help solve and maintain, and independent of the creases productivity. Thus, the UNIX critical software issues. First, a histor- hardware on which it runs. As the system is an ideal candidate to serve ical overview. price of software rapidly outpaces as a solution to the software crisis. that of computers, the need to in- Microsof t plans to make the XENIX Origins of the UND( 0s crease software productivity and operating system (which is an The UNIX operating system was reduce duplication of effort has enhanced version of the UNIX originally developed at Bell Lab- become paramount. system) into a commercial standard. oratories by Ken Thompson, an Microsof t's XENIX operating And, in addition to supporting and employee engaged in various pro- system offers one solution to the soft- enhancing the operating system gramming research projects. With ac- ware crisis developing in the cess to an abandoned DEC PDP-7 microcomputer world. Unlike the computer that had no software, operating systems offered for &bit Thompson decided in 1969 to write a machines, the XENIX system is a The XENIX system Is set of programs that would aid him in powerful multiuser timesharing one approach to software research. Over a period of system with hundreds of utilities and several years, and with the help of is the basis for a highly productive solvlng the software fellow researcher Dennis Ritchie, this software development environment crlsls developlng In the set of programs evolved into a full and a general-purpose applications microcomputer world. operating system. By 1972, it was system. recoded for the DEC PDP-11 com- The XENU operating environment puter in a newly designed high-level combines two key elements: the language, called C. The system design of the widely acclaimed UNIX proper, Microsoft will adapt hii- gained recognition within the Labs operating system and the inclusion level languages, such as its BASIC in- and their parent company, Western of the major high-level languages that terpreter and compiler, FORTRAN, Electric. are standard within the 8-bit Pascal, and COBOL, and other soft- Word of the quality of Thompson microcomputer world (see figure 1). ware tools, such as data-base man- and Ritchie's UNIX operating system I Microsoft's transport of the XENIX agement and communications soft- spread rapidly. Universities, in par- system to major 16-bit micropro- ware, to run under the XENIX operat- ticular, expressed interest in obtain- cessors has made it the first ing system. ing UNIX, and in 1973, Western Elec- 1 hardware-independent operating To understand the elegance of the tric agreed to distribute the system to system. basic UNIX design and the further nonprofit organizations and prompt- The heart of the XENU system is enhancements in the XENIX system, ly licensed several dozen educational .-,u,i the UNIX operating system developed we must take a closer look at the soft- institutions, including Columbia ' ; at Bell Laboratories and licensed by ware. In this article, I will describe University, the University of Alberta .-3 Western Electric. The UNIX system's the main features in the UNIX (Canada), The Children's Museum elegant design combines power, flex- operating system, discuss some of its (Boston), Princeton University, and v- strengths and weaknesses, and con- Harvard University. By 1975, UNIX 4F1 UNlX is a trademark of Bell Laboratories. had become sufficiently popular in XENlX is a trademark of Microsoft. clude with a discussion of the evolu- tion of the XENIX operating environ- the academic world to justify the 248 June 1981 O BYEPublications lnc XENlX OPERATING ENVIRONMENT I I I I I USER- UNlX UNlX V7 MICROSOFT MICROSOFT . V7 0s SOFTWARE SUPPORT LANGUAGES ~~~~!j,\\E~ I 1 I I Figure 1: Microsoft's ~ENIXoperating system. The five "layers" of the XENlX software structure are shown. XENIX, a superset of Bell Laboratories' UNlX operating system developed in the early 1970s, has a hierarchical structure. Each of the five layers depends on the layers beneath it for its operation. The bottom two layers represent the latest version of UNIX (version 7). The remaining three layers are the refinements that combine to make the XENlX system. Circle 85 on lnauiw card. creation of a UNIX users' organiza- dard industry version of UNIX that tion, later called USENIX. can provide a highly productive en- DISCOUNT The first public release of the UNIX vironment worthy of meeting the operating system, labeled version 5, challenges of software development Computers was an unpolished snapshot of a in the 1980s. from research project that was still evolv- ing. It was replaced in 1975 with ver- UND( Design Goals HAWAII sion 6, a system that is still operating Two aspects of UNIX's origin have today at many sites. UNIX continued contributed to its design: (1) it was to evolve, benefitting from the feed- created in a few man-years by two back it received from scores of inter- people, and (2) the implementers nal and external test sites. were also major users of the system. In January 1979, Western Electric The result is a polished, consistent, released version 7. By this time, hun- coherent design. UNIX'achieves great dreds of man-years' effort has been power and flexibility, including com- expended on UNWs design and soft- patible interfacing between all its $1 180.00" ware utilities, with most of the system features, without resorting to a large, isk coded in C. Research had proven that complex program. An experienced Lang Sys. ::z:::l UNIX was compatible with the con- system programmer can understand l nteger Card $158.00* cepts of memory-limited computers, the entire operating system in weeks, machine transportability, networks, rather than months. Apple Soft Card $158.00* and multiple-processor designs. The UNIX system's design goals Unfortunately, there was no single unite various features supported by standard design for UNIX. Because the UNIX sytem into a consistent and the operating system was simple and simple whole. The first design goal is easy to change, almost every site to support a very basic level of func- altered it to meet their specific needs. tionality within the operating system Harvard, the University of California itself, relying on normal user pro- at Berkeley, and the RAND Corpora- grams to provide sophistication. Such tion each offered a set of modifica- features as line printer queuing, tions. A number of incompatible ver- login/logout, monitor commands, sions of UNIX existed within Western and file access methods are im- Electric. plemented as normal user programs In addition, there has been a legal instead of operating-system func- impediment to the UNIX system's tions. This approach, which reduces distribution. The system is available the overall complexity of the system, essentially free-of-charge for educa- has several advantages. Functions are tional institutions. Legally, however, more modular, and therefore easier to Western Electric cannot be in the soft- debug, features can be altered and ware business, so the commercial upgraded without stopping the world is offered the operating system operating system, and alterations under noncompetitive terms: source made to one feature are less likely to code as is and no warranty, support, affect the rest of the system. Finally, or maintenance-a steep fee for soft- individual users may create personal ware that was never intended to serve versions of certain features. commercial applications outside of The second design goal is gen- Western Electric. erality-that is, having a single It had become clear that the sup- method serve a variety of related pur- port of a commercial software com- poses. For example, the same system Computer pany was essential if UNIX was to calls are used to read and write disk become a software standard. In files, devices, and interprocess August of 1980, Microsoft announced message buffers. Likewise, the same Warehouse that it would offer and support naming, aliasing, and access protec- XENIX, a commercial version of the tion mechanisms apply to data files, P.O. Box 1777 operating system, on 16-bit micro- directories, and devices. As a final Honolulu, HI 96806 processors. Working closely with example, the same mechanism is used Western Electric and a newly formed to trap software interrupts, user abort (808) 523-1552 commercial users' organization, requests, and processor traps. The Microsoft intends to establish a stan- benefits of generality extend well 252 Jne lam B BYTE Publieatians lnc Circle 1'8 on inquiry card. d beyond the simplicity of design; output and the commands needed to number of characters, words, and UNIX programming style is notably produce it, and yields all the benefits lines in a file, that we only want to see flexible, extensible, easily learned, of modular solutions to complex the number of lines. Thus, this com- and easily debugged. problems. posite command prints a number The third goal is to accomplish The vast number of utilities pro- which.is the number of users on the large tasks by combining several vided with the system and the ease of system: small tasks whenever possible. linking them together via pipes pro- UNIX's filters are an excellent exam- vide a surprising amount of func- ple, A filter is a program that pro- tionality. For example, to find out cesses a single stream of input to how many people are currently using generate one output stream.