Java Reference
In-Depth Information
FIGURE 1.1
A simplified view of a computer system
The program is stored on some secondary memory device, such as a hard disk.
When you instruct the computer to execute your program, a copy of the program
is brought in from secondary memory and stored in main memory. The CPU reads
the individual program instructions from main memory. The CPU
then executes the instructions one at a time until the program ends.
The data that the instructions use, such as two numbers that will
be added together, also are stored in main memory. They are either
brought in from secondary memory or read from an input device
such as the keyboard. During execution, the program may display
information to an output device such as a monitor.
The process of executing a program is fundamental to the operation of a com-
puter. All computer systems basically work in the same way.
KEY CONCEPT
The CPU reads the program
instructions from main memory,
executing them one at a time until
the program ends.
Software Categories
Software can be classified into many categories using various criteria. At this point
we will simply differentiate between system programs and application programs.
The
operating system
is the core software of a computer. It performs two
important functions. First, it provides a
user interface
that allows the user to inter-
act with the machine. Second, the operating system manages computer resources
such as the CPU and main memory. It determines when programs are allowed
to run, where they are loaded into memory, and how hardware devices commu-
nicate. It is the operating system's job to make the computer easy to use and to
ensure that it runs efficiently.
Several popular operating systems are in use today. The Windows
operating system was developed for personal computers by Microsoft,
which has captured an operating system market share of almost
90%. Various versions of the Unix operating system are also quite
KEY CONCEPT
The operating system provides
a user interface and manages
computer resources.
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