Introducing Operating Systems
The operating system is a set of programs which manages the operation of a computer. It sits between the hardware and the user to provide an interface by which to control processes and devices on the computer. The operating system has four primary functions which are all dealt with in separate posts.
- Process Management [Read More]
- Memory Management [Read More]
- I/O Control [Read More]
- File Management [Read More]
Interfaces
The interface of an operating system is the way in which it can communicate with the user. The interface may be command line, graphical or take the form of job control language.
Command Line Interface.
Here the user accesses the computer via a terminal which provides a text input and output facility. A command line interpreter (CLI) is responsible for identifying the correct process the user has requested.
Job Control Language
In a JCL interface a user has no direct way of interacting with the computer; instead they prepare a program using a series of instructions, and allow this program to be executed with any results being prepared for viewing at a later date. A JCL program will have to specify things such as:
- Who owns the job
- What priority the job has
- The names of any data files used.
- Action to take if the task does not execute properly
- The maximum resources to allocate to the job
Graphical User Interfaces
A GUI allows the user to interact in more ways with the computer. This is often by use of a WIMP (Windows, Icons, Mouse and Pointers) system which is more intuitive than a command line system. GUIs do however use far more resources than a basic interface and can be inefficient when it comes to repeating processes numerous times.
Modes of Operation
- Batch. This is where a job (often defined in JCL) runs from beginning to end without direct user intervention.
- Interactive. This is where the user interacts directly with the system, entering commands and data whilst the program executes.
- Real Time. This is where data is processed with minimal delay so the system can respond instantly to changes in variables.
- Single User. The OS can only allow one user to be using the machine at a given time.
- Single Process. The OS can only execute a single process at a time.
- Multi Programming. The OS appears to be able to process two or more programs concurrently.
- Multi User. The OS allows two or more users to be communicating with the computer simultaneously.
- Multi Tasking. The OS allows the user to be working on two or more (related) tasks simultaneously, and allows these tasks to interact.
- Network. A computer which wishes to communicate with other computers must run network software to enable such communication
References:
- Janet Lavery - Durham University Computer Systems, Operating Systems Lecture 1, 2007
- A2 Computing Revision - Paul Nicholls - http://resources.r9paul.org/ASA2/Computing/A2ComputingRevision.pdf