>Well, I think so far all we've come up with is "I'll know an operating
>system when I see one". We've had both opinions stated, but no one defined
>exactly what an operating system is and used that definition to support
>either side. Would those who have stated an opinion please support that
>position with a definition?
These aren't opinions Earl, there is no debate about this. As David G.
stated there were debates among PC hobbyist about this issue but no serious
organization like PC Mag ever endorsed this theory and Microsoft has never
called Windows 1-3x a operating system. As has been previously stated Win
1-3x was called an Environment.
There are a lot of definitions of the term operating system but I think Jim
has provided the List with a very good explanation of what makes a OS an OS.
However I have appended this post with a more comprehensive definition of
the term Operating System.
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operating system
The master control program that runs the computer. It is the first program
loaded when the computer is turned on, and its main part, called the
kernel, resides in memory at all times. It may be developed by the vendor
of the computer it's running in or by a third party.
It is an important component of the computer system, because it sets the
standards for the application programs that run in it. All programs must
"talk to" the operating system.
The main difference between an operating system and a network operating
system is its multiuser capability. Operating systems, such as Macintosh
System 7, DOS and Windows, are single user, designed for one person at a
desktop computer. Windows NT and UNIX on the other hand are network
operating systems, because they are designed to manage multiple user
requests at the same time.
An operating system is also called an executive or supervisor. Operating
systems perform the following functions.
User Interface
The user interface, or shell, provides the interaction between the user and
the operating system. Operating systems may allow for different shells;
for example, DOS and UNIX provide command-driven interfaces but can host
other shells that provide a menu-driven or graphical interface. Even
Windows, which is graphics based to begin with, allows other shells to
provide an interface to the user.
Job Management
Job management controls the running of programs. Which one gets executed
first, then next. In small computers, the operating system responds to
interactive commands from the user and loads the requested application
program into memory for execution. Larger computers are more oriented to
accepting a batch of instructions. For example, job control language (JCL)
may describe the programs that must be run for an entire shift. In some
cases, the output of one program may then be input into another and so on.
Task Management
Task management controls the simultaneous execution of programs. In single
tasking computers, the operating system has virtually no task management to
do, but in multitasking computers, it is responsible for the concurrent
operation of one or more programs (jobs). Advanced operating systems have
the ability to prioritize programs so that one job gets done before the other.
In order to provide users at terminals with the fastest response time,
batch programs can be put on lowest priority and interactive programs can
be given highest priority. Advanced operating systems can be fine tuned by
the computer operator so that a specific job can be speeded up or slowed down.
Multitasking is accomplished by executing instructions for one function
while data is coming into or going out of the computer for another. Large
computers are designed to overlap these operations, and data can move
simultaneously in and out of the computer through separate channels with
the operating system governing these actions.
In small computers, the operating system can monitor idle time when a
user is interactively working with a program to execute another program in
the background. Even the milliseconds between keystrokes can be used for
something else. A user, pausing at the keyboard for just a couple of
seconds, is light years to the computer, which can use that time to execute
hundreds of thousands of instructions.
Data Management
Data management keeps track of data on the disk; hence the term DOS, or
disk operating system. The application program does not know where the
data is actually stored or how to get it. That knowledge is contained in
the operating system's access method, or device driver, routines. When a
program is ready to accept data, it signals the operating system with a
message. The operating system finds the data and delivers it to the
program. Conversely, when the program is ready to output, the operating
system transfers the data from the program onto the available space on disk.
Device Management
Device management controls the input and output of data to and from the
peripheral devices. The operating system is responsible for providing
central management of all devices, not just disk drives. When a new type
of peripheral is added to the computer, the operating system is updated
with a new driver for that device. The driver contains the specific
instructions necessary to run it. The operating system calls the drivers
for input and output, and the drivers talk to the hardware.
In the DOS world, software developers often bypassed the operating system
and addressed the hardware directly to improve performance. In addition,
DOS does not support device management for all peripheral devices,
requiring application developers to support myriads of brands of hardware.
This is a major reason why DOS gave way to Windows, which provides
centralized device management.
Security
Multiuser operating systems maintain a list of authorized users and provide
password protection to unauthorized users who may try to gain access to the
system. Large operating systems also maintain activity logs and accounting
of the user's time for billing purposes. They also provide backup and
recovery routines to start over again in the event of a system failure.
History
The earliest operating systems were developed in the late 1950s to manage
tape storage, but programmers mostly wrote their own I/O routines. In the
mid 1960s, operating systems became essential to manage disks, complex
timesharing and multitasking systems.
Today, all multi-purpose computers from micro to mainframe use an
operating system. Special-purpose devices (appliances, games, toys, etc.)
generally do not. They usually employ a single program that performs all
the required I/O and processing tasks.
Common Operating Systems
PCs primarily use DOS, Windows 3.x, Windows 95/98, Windows NT and OS/2 with
all the various Windows versions being the most popular. Macintoshes use
the Mac OS (System 7, System 8, etc.). Minicomputers and workstations use a
variety of UNIX operating systems, and IBM mainframes primarily use OS/390
(formerly MVS).
In the past, when a vendor introduced a new operating system, users had
little understanding of this behind-the-glass-enclosed-datacenter
phenomenon. Today, it is squarely in their hands.
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