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<LI>
<A HREF="#I1">1 — Operating System</A></LI>
<UL>
<UL>
<UL>
<UL>
<LI>
<A HREF="#I3">By Rachel and Robert Sartin</A></LI></UL></UL>
<LI>
<A HREF="#I4">What is an Operating System?</A></LI>
<UL>
<LI>
<A HREF="#I5">Hardware Management, Part 1</A></LI>
<LI>
<A HREF="#I6">Process Management</A></LI></UL>
<LI>
<A HREF="#I7">The UNIX Operating System</A></LI>
<LI>
<A HREF="#I8">The History of UNIX</A></LI>
<UL>
<LI>
<A HREF="#I9">The Early Days</A></LI>
<LI>
<A HREF="#I10">Berkeley Software Distributions</A></LI></UL>
<LI>
<A HREF="#I11">UNIX and Standards</A></LI>
<UL>
<LI>
<A HREF="#I12">UNIX for Mainframes and Workstations</A></LI>
<LI>
<A HREF="#I13">UNIX for Intel Platforms</A></LI>
<LI>
<A HREF="#I14">Source Versions of "UNIX"</A></LI>
<LI>
<A HREF="#I15">Making Changes to UNIX</A></LI></UL>
<LI>
<A HREF="#I16">Introduction to the UNIX Philosophy</A></LI>
<UL>
<LI>
<A HREF="#I17">Simple, Orthogonal Commands</A></LI>
<LI>
<A HREF="#I18">Commands Connected Through Pipes</A></LI>
<LI>
<A HREF="#I19">A (Mostly) Common Option Interface Style</A></LI>
<LI>
<A HREF="#I20">No File Types</A></LI></UL>
<LI>
<A HREF="#I21">Summary</A></LI></UL></UL></UL>
<H1 ALIGN="CENTER">
<CENTER><A ID="I1" NAME="I1">
<BR>
<FONT SIZE=5><A ID="I2" NAME="I2"></A><B>1 — Operating System</B>
<BR></FONT></A></CENTER></H1>
<H5 ALIGN="CENTER">
<CENTER><A ID="I3" NAME="I3">
<FONT SIZE=3><B>By Rachel and Robert Sartin</B>
<BR></FONT></A></CENTER></H5>
<H3 ALIGN="CENTER">
<CENTER><A ID="I4" NAME="I4">
<FONT SIZE=4><B>What is an Operating System?</B>
<BR></FONT></A></CENTER></H3>
<P>An operating system is an important part of a computer system. You can view a computer system as being built from three general components: the hardware, the operating system, and the applications. (See Figure 1.1.) The hardware includes pieces such as
a central processing unit (CPU), a keyboard, a hard drive, and a printer. You can think of these as the parts you are able to touch physically. Applications are why you use computers; they use the rest of the system to perform the desired task (for
example, play a game, edit a memo, send electronic mail). The operating system is the component that on one side manages and controls the hardware and on the other manages the applications.
<BR></P>
<P>
<BR><B><A HREF="01unx01.gif">Figure 1.1. Computer system components.</A></B>
<BR></P>
<P>When you purchase a computer system, you must have at least hardware and an operating system. The hardware you purchase is able to use (or run) one or more different operating systems. You can purchase a bundled computer package, which includes the
hardware, the operating system, and possibly one or more applications. The operating system is necessary in order to manage the hardware and the applications.
<BR></P>
<P>When you turn on your computer, the operating system performs a series of tasks, presented in chronological order in the next few sections.
<BR></P>
<H4 ALIGN="CENTER">
<CENTER><A ID="I5" NAME="I5">
<FONT SIZE=3><B>Hardware Management, Part 1</B>
<BR></FONT></A></CENTER></H4>
<P>One of the first things you do, after successfully plugging together a plethora of cables and components, is turn on your computer. The operating system takes care of all the starting functions that must occur to get your computer to a usable state.
Various pieces of hardware need to be initialized. After the start-up procedure is complete, the operating system awaits further instructions. If you shut down the computer, the operating system also has a procedure that makes sure all the hardware is shut
down correctly. Before turning your computer off again, you might want to do something useful, which means that one or more applications are executed. Most boot ROMs do some hardware initialization but not much. Initialization of I/O devices is part of the
UNIX kernel.
<BR></P>
<H4 ALIGN="CENTER">
<CENTER><A ID="I6" NAME="I6">
<FONT SIZE=3><B>Process Management</B>
<BR></FONT></A></CENTER></H4>
<P>After the operating system completes hardware initialization, you can execute an application. This executing application is called a process. (See Chapter 18, "What Is a Process?") It is the operating system's job to manage execution of the
application. When you execute a program, the operating system creates a new process. Many processes can exist simultaneously, but only one process can actually be executing on a CPU at one time. The operating system switches between your processes so
quickly that it can appear that the processes are executing simultaneously. This concept is referred to as time-sharing or multitasking.
<BR></P>
<P>When you exit your program (or it finishes executing), the process terminates, and the operating system manages the termination by reclaiming any resources that were being used.
<BR></P>
<P>Most applications perform some tasks between the time that the process is created and the time that it terminates. To perform these tasks, the program makes requests to the operating system and the operating system responds to the requests and allocates
necessary resources to the program. When an executing process needs to use some hardware, the operating system provides access for the process.
<BR></P>
<P><B>Hardware Management, Part 2</B>
<BR></P>
<P>To perform its task, a process may need to access hardware resources. The process may need to read or write to a file, send data to a network card (to communicate with another computer), or send data to a printer. The operating system provides such
services for the process. This is referred to as resource allocation. A piece of hardware is a resource, and the operating system allocates available resources to the different processes that are running.
<BR></P>
<P>See Table 1.1 for a summary of different actions and what the operating system (OS) does to manage them.
<BR></P>
<UL>
<LH><B>Table 1.1. Operating system functions.</B>
<BR></LH></UL>
<TABLE BORDER>
<TR>
<TD>
<PRE><I>Action</I>
<BR></PRE>
<TD>
<PRE><I>OS Does This</I>
<BR></PRE>
<TR>
<TD>
<P>You turn on the computer</P>
<TD>
<P>Hardware management</P>
<TR>
<TD>
<P>You execute an application</P>
<TD>
<P>Process management</P>
<TR>
<TD>
<P>Application reads a tape</P>
<TD>
<P>Hardware management</P>
<TR>
<TD>
<P>Application waits for data</P>
<TD>
<P>Process management</P>
<TR>
<TD>
<P>Process waits while other process runs</P>
<TD>
<P>Process management</P>
<TR>
<TD>
<P>Process displays data on screen</P>
<TD>
<P>Hardware management</P>
<TR>
<TD>
<P>Process writes data to tape</P>
<TD>
<P>Hardware management</P>
<TR>
<TD>
<P>You quit, the process terminates</P>
<TD>
<P>Process management</P>
<TR>
<TD>
<P>You turn off the computer</P>
<TD>
<P>Hardware management</P></TABLE>
<P>From the time you turn on your computer until you turn it off, the operating system is coordinating the operations. As hardware is initialized, accessed, or shut down, the operating system manages these resources. As applications execute, request, and
receive resources, or terminate, the operating system takes care of these actions. Without an operating system, no application can run and your computer is just an expensive paperweight.
<BR></P>
<H3 ALIGN="CENTER">
<CENTER><A ID="I7" NAME="I7">
<FONT SIZE=4><B>The UNIX Operating System</B>
<BR></FONT></A></CENTER></H3>
<P>The previous section looked at an operating system in general. This section looks at a specific operating system: UNIX. UNIX is an increasingly popular operating system. Traditionally used on minicomputers and workstations in the academic community,
UNIX is now available on personal computers, and the business community has started to choose UNIX for its openness. Previous PC and mainframe users are now looking to UNIX as their operating system solution. This section looks at how UNIX fits into the
operating system model.
<BR></P>
<P>UNIX, like other operating systems, is a layer between the hardware and the applications that run on the computer. It has functions that manage the hardware and functions that manage executing applications. So what's the difference between UNIX and any
other operating system? Basically two things: internal implementation and the interface that is seen and used by users. For the most part this book ignores the internal implementation. If you wish to know these details, many texts exist that cover them.
The interface is what this book describes in detail. The majority of UNIX users need to be familiar with the interface and need not understand the internal workings of UNIX.
<BR></P>
<P>The UNIX system is actually more than strictly an operating system. UNIX includes the traditional operating system components. In addition, a standard UNIX system includes a set of libraries and a set of applications. Figure 1.2 shows the components and
layers of UNIX. Sitting above the hardware are two components: the file system and process control. Next is the set of libraries. On top are the applications. The user has access to the libraries and to the applications. These two components are what many
users think of as UNIX, because together they constitute the UNIX interface.
<BR></P>
<P>
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