Operating System Concepts PDF

21/11/2021 OPERATING SSYSTEM: is the main program that controls the execution of user applications and enables the user access hardware and software resources of a computer. 1  21/11/2021
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21/11/2021 OPERATING SSYSTEM: is the main program that controls the execution of user applications and enables the user access hardware and software resources of a computer. 1  21/11/2021
Resources Under Os Control  Processor  Main memory  Storage devices  Input devices / Output devices  Communication devices 2  21/11/2021
Processor Scheduling This refers to allocating each job awaiting for execution processor time at each given interval. Jobs are scheduled according to priority. 3  21/11/2021
Resource Allocation Each available resource in a computer is given a unique identification number called Interrupt Request (IRQ). OS uses IRQ number to identify resources being requested.
Memory Management OS determines which task remains in memory awaiting for execution and which one should be kicked out back to secondary storage. 4  21/11/2021
Input/output Management OS – coordinates between the various I/O devices and other peripheral devices making sure that data is transmitted securely.
Communication Control and Management OS is responsible for managing various communication devices and provide an environment within which communication protocols operate. 5  21/11/2021 Error Handling OS monitors status of computer system by performing audit checks on users, hardware and software. …. And alerts user on errors arising out of illegal operations, on hardware or software failure.
Interrupt Handling Interrupt is a break from normal sequential processing of instructions in a program. A critical request causes the processor to stop executing the current process, before returning the control back to the process that was initially interrupted. 6  21/11/2021
Os – classified according to:  Number of tasks  Number of Users  User Interface.
Single program Os – Allows for processing one application program in the main memory at a time. User can only run one interactive program at a time. Example – Ms DOS
Multitasking Os – Allows a single CPU to execute what appears to be more than one application program apparently at the same time. Through processor scheduling Os allocates a time slice to each ready task. CPU switches attention between programs as directed by the Os 7  21/11/2021
Single User Os – designed to be used by only one person. Also runs only one user application at a time.
Multi-user Os – Also called multi-access Os. Allows more than one user to interactively use the computer. Example = server Os such as Windows server 2003. Useful in a network environment and can be accessed by all users in an organisation. Others include: UNIX, Windows NT, Linux
User Interface refers to interaction between the user and the computer. User interface determines the friendliness of computer software.
Types of User Interfaces:
Command-line user Interface.
Menu driven Interface
Graphical User Interface (GUI) 8  21/11/2021
Command-line interface:  Allows user type a command at a command prompt. The computer reads the typed command from the command line and executes it.  For it to be friendly, the words used should be descriptive verbs e.g. PRINT, COPY.  Unique abbreviations can also be used e.g. DEL, REN,  Example of command-line interface: Ms DOS.  Not popular because it is difficult to remember commands, cannot process complex graphics and hardly make use of emerging hardware and software technologies.
Menu Driven Interface – provide the user with a list of options to choose from.
Is suitable for beginners who may find it hard to recall commands. 9  21/11/2021
Graphical User Interface (GUI)  Besides menus GUI makes use rectangular work areas called Windows, graphical objects called Icons and most commands are executed using a pointing device.  Usually abbreviated as WIMP for Windows, Icons, Menus and Pointers.  Examples: Ms Windows versions – 2000, XP, Vista, Windows 7; Apple Mac Os, Linux.
Factors to Consider:  Hardware configuration – CPU, memory, HDD capacity  Type of computer – make and type.  Application software to be installed.  User friendliness  Documentation available.  Cost of OS  Reliability and security provided by the OS  Number of processors and hardware it can support.  Number of users it can support. 10  21/11/2021 THE END 11