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Comparison between real time and time sharing operating system

Protection and security

• Protection refers to a mechanism for controlling the access of program s processes, or users to the resources defined by computer system.

• The concept of protection came with the advent of multiprogramming where several processes compete for the use of CPU.

• the purpose was to confine each users program to its assigned areaof memory so that the programs cannot interface and harm each other.

• Protection in main memory is particularly important because of address translation. The purpose of protection is to allow concurrently running process to share the common physical address space.

• Protection also ensure that only process that have gained proper authorization from the operating system can operate on memory segment , the CPU, files and other resources.

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Shortest Job First Scheduling (SJF)

Shortest Job First Scheduling (SJF) · SJF ia also known as shortest-job-next(SJN) algorithm and is faster than FCFS. · In SJF, the process with the least estimated execution time is selected from the ready queue for execution. · For this, SJF algorithm associates with each process, the length of its next CPU burst. When the CPU is available, it is assigned to the process that has the smallest next CPU burst. · If tow processes have the same length of next CPU burst ,FCFS scheduling algorithm is used to break the tie. · SJF algorithm can be preemptive or non-preemptive. Non-preeptive SJF · In non-preemptive SJF, scheduling, CPU is always assigned to the ...

Scheduling Algorithms

Scheduling Algorithms CPU scheduling algorithm deal with the problem of deciding which of the processes in the ready queue is to be allocated the CPU . six commonly used scheduling algorithms are: 1. first-come First-served(FCFS) 2. Shortest job First(SJF) 3. Priority scheduling 4. Round-Robin Scheduling(RR) 5. Multi-Level Queue Scheduling(MLQ) 6. Multi-Level Feedback Queue Scheduling (MFQ) First-Come First-Served Scheduling (FCFS) · It is simplest and the most straight forward of all scheduling algorithms. · In this scheduling, the process that request the CPU first is allocated CPU first. Thus the name first come first served. · We can say that in FCFS scheduling, a process is allocated CPU time according to the arrival time of a process. · The implementation of FCFS policy is easily manged with a FIFO queue...

Priority scheduling

Priority scheduling In priority scheduling , a priority is associated with all processes. Process are executed in sequence according to their priority. The CPU time is allocated to the process with highest priority. If the priority of two or more processes are equal than the process that has been inserted first into the ready queue is selected for execution. In other words, FCFS scheduling is performed when wo or more processes have same priority. The priorities are implemented as affixed range of numbers such as 0to 7 or 0 to 4,095. In other system, a low number indicates a high priority . in that case,a process with priority 0 is executed first. Priorities can be defined in two ways : internal or externall. ...

Multi user Operating System

Multi user operating system · In a multi-user operating system, multiple number of user can access different resources of a computer at a same time. · The access is provided using a network that consists of various personal computer attached to a mainframe computer system. diagram of multi -user operating system · The various personal computer can send and receive information to mainframe computer system. · The example of multi-user OS are UNIX, windows 2000,novell netware. sing...

Exokernel architecture

Exokernel architecture Most of us know what kernels are and how do they work to make programmers’ lives easier. But, how many of us know what exokernels are? I hope you will be able to get a brief introduction on this terminology through this blog. Let’s start with a brief introduction on kernel. What is a kernel? A kernel is the foundational layer of an operating system that functions at a basic level, communicating with hardware and managing resources, such as CPU and the memory. It works as an interface between the user application and the hardware. There are two main types of kernel 1. Micro kernel 2. Monolithic Kernel 1. Monolithic architecture 2. Layerd archtecture . 3. Virtual machine architecture 4. Exokernel architecture 5. Client server architecture 6. Micro kernel architecture Now let’s head into our main focus. What is an Exokern...