Operating System Concepts Three User Interfaces Command-line Job-Control Language (JCL) Graphical User Interface (GUI)

Command Line Interface (CLI) An interactive terminal allows the system to prompt What does the end user have to do? –Then the end user types a command via a keyboard. A well known example is MS-DOS

Command Line Interface (CLI) House-keeping command like… C:\>Copy Project. *a: –This will cause all files named Project to be copied to the current folder on the A-drive > is the command prompt C:\ is the pathname for the current folder The command-line interpreter (CLI) performs the task of identifying and executing the command

Command Line Interface (CLI) Why could this type of interface be considered the least user friendly? –Large range of text-based commands –Understand the syntax that goes with them An advantage of this type of interface is? –Direct control of the O.S. –There are more commands available than can be displayed on the screen at any one time –The user does not have to follow a sequence of menus or windows and this saves time

Job Control Language Some sophisticated Op.Systems allow the user to control the way the O.S. copes with tasks or jobs –The user has no direct interaction with the computer system but uses a series of instructions to alter the priority of the tasks These instructions are prepared off-line using a JCL to describe the system requirements of the task A user’s job is executed, the execution is guided by the JCL-prepared description and the results are made at a later time via an off-line medium (line printer paper) –See chapter page 271 for an example

Graphical User Interface A GUI allows the end user to interact with the system using windows, icons, menus and a pointer to control the O.S. What can icons represent? –Programs –Groups of programs –Folders –Devices –Files A GUI is also sometimes known as WIMP: which means? Windows, Icons, Menu (or Mouse) and Pointer

Graphical User Interface How is selection achieved? –Moving a pointer with a mouse and clicking on a button What type of computer user is the GUI more suitable for? Why –The interface is more intuitive through the use of metaphors and graphical symbols –Only valid options are available and the layout is consistent –On-line help –Command representation in applications Novice user

Graphical User Interface What are the disadvantages with a GUI? –Use more immediate access store and secondary store –Require a more powerful processor and better graphics display –Slower when executing a command because a lot more interpretation takes place –Can be irritating to use for simple tasks because a greater number of operations are required

The Process Concept This is important in multi-programming operating systems What type of an operating system is this? –This is an O.S. that allows a number of programs to appear to be running simultaneously on one computer Definition: a process is a program actually running on the CPU, even though it might be waiting for I/O at a particular moment

The Process Concept Fine! What does that mean? –a Pascal Compiler may be executed by several people simultaneously on a network –There will only be one copy in memory –Different parts of it will be used by several different people to compile their programs –They will share the same code –Each instance of the program running will be a process, with separate data areas maintained for each execution –A program working this way is said to be re- entrant

Runnable RunningSuspended Time-slice exceeded Event completed I/O or event request A process is dynamic Process can contain one or more threads. Each thread has a scheduling state OS maintains info about a process within a data structure called a process control block Each thread has its own thread control block