Page 29 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes
Figure 1.6: 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

1.7.5.3 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.
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 “multi-tasking” 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.
Management systems are implicitly designed to be used by multiple users, typically one system
administrator or more and an end-user community.
It’s important to differentiate between multi-user operating systems and single-user operating
systems that support networking. Windows 2000 and Novell Netware can each support hundreds
or thousands of networked users, but the operating systems themselves are not true multi-user
operating systems. The system administrator is the only “user” for Windows 2000 or Netware.
The network support and all of the remote user logins the network enables are, in the overall
plan of the operating system, a program being run by the administrative user.

1.7.5.4 Multiprogramming

Disjoint Processes:
Our starting point is the concurrent statement:
cobegin S1; S2; . . . ; Sn coend

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