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Exposure to Computer Disciplines

Notes An early example of a large-scale real-time operating system was Transaction Processing Facility.
Current users include Sabre (reservations), Amadeus (reservations), VISA Inc (authorizations),
Holiday Inn (central reservations), CBOE (order routing), Singapore Airlines, KLM, Qantas,
Amtrak, Marriott International , Worldspan and the NYPD (911 system).

3.2.2 Single User, Single Task

As the name implies, this operating system is designed to manage the computer so that one
user can effectively do one thing at a time. The Palm OS for Palm handheld computers is a good
example of a modern single-user, single-task operating system.

Figure 3.6: The Palm

Treo 700p is one of many Smartphones produced that combines Palm PDA functions with a cell
phone, allowing for built-in voice and data.
3.2.3 Single User, Multitasking

This is the type of operating system most people use on their desktop and laptop computers today.
Microsoft’s Windows and Apple’s Mac OS platforms are both examples of operating systems
that will let a single user have several programs in operation at the same time. For example, it’s
entirely possible for a Windows user to be writing a note in a word processor while downloading
a file from the Internet while printing the text of an e-mail message.

3.2.3.1 Multi-User
Multi-user is a term that defines an operating system or application software that allows concurrent
access by multiple users of a computer. A multi-user operating system allows many different
users to take advantage of the computer’s resources simultaneously. The operating system must
make sure that the requirements of the various users are balanced, and that each of the programs
they are using has sufficient and separate resources so that a problem with one user doesn’t affect
the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are
examples of multi-user operating systems.
Time-sharing systems are multi-user systems. Most batch processing systems for mainframe
computers may also be considered “multi-user”, to avoid leaving the CPU idle while it
waits for I/O operations to complete. However, the term “multitasking” is more common
in this context.

An example is a Unix server where multiple remote users have access (such as via Secure Shell)
to the Unix shell prompt at the same time. Another example uses multiple X Window sessions
spread across multiple terminals powered by a single machine - this is an example of the use of
thin client.

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