Lec2.CS604 - Operating Systems[CS-604 Lecture No 2...

Operating Systems [CS-604] Lecture No. 2
Operating Systems
Lecture No. 2
Reading Material
? Operating Systems Concepts, Chapter 1
? PowerPoint Slides for Lecture 2
Summary
? Single-user systems
? Batch systems
? Multi programmed systems
? Time-sharing systems
? Real time systems
? Interrupts, traps and software interrupts (UNIX signals)
? Hardware protection
Single-user systems
A computer system that allows only one user to use the computer at a given time is
known as a single-user system . The goals of such systems are maximizing user
convenience and responsiveness, instead of maximizing the utilization of the CPU and
peripheral devices. Single-user systems use I/O devices such as keyboards, mice, display
screens, scanners, and small printers. They can adopt technology developed for larger
operating systems. Often individuals have sole use of computer and do not need advanced
CPU utilization and hardware protection features. They may run different types of
operating systems, including DOS, Windows, and MacOS. Linux and UNIX operating
systems can also be run in single-user mode.
Batch Systems
Early computers were large machines run from a console with card readers and tape
drives as input devices and line printers, tape drives, and card punches as output devices.
The user did not interact directly with the system; instead the user prepared a job, (which
consisted of the program, data, and some control information about the nature of the job
in the form of control cards) and submitted this to the computer operator. The job was in
the form of punch cards, and at some later time the output was generated by the system—
user didn’t get to interact with his/her job. The output consisted of the result of the
program, as well as a dump of the final memory and register contents for debugging.
To speed up processing, operators batched together jobs with similar needs, and ran
them through the computer as a group. For example, all FORTRAN programs were
complied one after the other. The major task of such an operating system was to transfer
control automatically from one job to the next. In this execution environment, the CPU is
often idle because the speeds of the mechanical I/O devices such as a tape drive are
slower than that of electronic devices. Such systems in which the user does not get to