Processors First-Come -First -- Served Fcfs This Essay

  • Length: 6 pages
  • Sources: 5
  • Subject: Education - Computers
  • Type: Essay
  • Paper: #64393819

Excerpt from Essay :


First-come -first -- served (FCFS)

This system is also called other names such as run-to-completion and run-until-done. It has its advantages and disadvantages. Advantages include the facts that it is the simplest scheduling algorithm with processes dispatched according to their arrival time on the queue and that once a process has a CPU it fulfills its task to completion. It is also simple to understand and write. In short, the FCS scheduling is fair and predictable.

Disadvantages, on the other hand, include the potential lengthiness of the tasks with some important jobs take secondary place to less important ones and longer jobs taking up an inordinate amount of time making shorter tasks wait.

I would not use FCFS in scheduling interactive users since it does not guarantee good response time and average time is often quite long. I would not use it in a modern operating system; it can, however, be embedded in other systems.

Round Robin scheduling (RRS)

Many prefer RRS since FCFS since processes whilst dispatched in a FIFO* manner are allocated a limited amount of CPU time that is called a "quantum" or a time-slice" of computer attention. If the process is incomplete by the time its CPU-allocation expires, the process is aborted and returned to the back of the queue whilst the task next in line is seen to. In this way, it has the advantages of FCFS without having its disadvantages.

On the other hand, setting the quantum too short causes too many context switches and redoes the efficiency of the CPU, but setting the quantum too long may cause the same problems as that of the FCFS. Either way, the average waiting time for RRS to complete its tasks is frequently quite long.

3. Shortest Process Next (SPN)-

Tasks that display shortest amount of time for completion are prioritized in order of importance so that the CPU processes tasks that have the smallest quantum first. I would use this process when running batch jobs where the amount of time of tasks is known ahead of time.

The disadvantages are that longer jobs may be more important than shorter ones, and that I would have to know, ahead of time, an approximation of the running time of each task. I cannot us SPN in a timesharing environment where reasonable response time must not be guaranteed nor can I use it in a development environment where I rarely know how my program will execute. However, in the production environment where the same jobs run regularly, I may be able to approximate performance based on past experience.

4. Shortest-Remaining Time Scheduling (SRT)

In this kind of scheduling, the process with the smallest approximation of run-time to completion is run next and the job is run to completion. The process may be preempted by a new arrival whose running time to completion is even shorter than that already in existence. SRT has higher overhead than SPN since it also handles occasional interruptions. The benefits are that arrival of small tasks will be seen to immediately, but longer jobs have longer waiting time therefore important tasks may be pushed to the side.

(Hot Recruiter; CPU Scheduling)

Rate Monotonic Scheduling (RMS) algorithm,

Static priorities are assigned to the task with the shorter the cycle, the higher the job's priority and preemption given to that task above that of the rest of the jobs. Rate monotonic analysis is used a scheduling guarantee for particular applications.

RMS works according to rate-monotonic analysis where threads have the following characteristics:

They do not share resources

Their deadlines are the same as periods

Tasks with highest static priority preempts other tasks

Thread operations such as context switch times are free and do not impact model.

RMS is a mathematical model that looks at a run modeling of all threads that are contained in the system and determines the amount of time needed for the threads in question. In mathematical terms, it resembles a queue of closed periods each with its own periodic task. In a case where deadlines are grater than periods this is known as an "open problem."

It resolves scheduling conflicts by static prioritization. This helps in many applications where resources are shared and RMS allocates priority inheritance in order to prevent deadlock. Other methods that it uses to prevent deadlock are to use lock-free algorithms or to avoid sharing a semaphore across threads that have different priorities. In this way, conflicts cannot happen in the first place.

Unix-like operating systems

I am familiar with these systems, which include Solaris, Linux, Mac, Plan, and Windows. They have a virtual file system which makes all the files on each of the devices seem to exist in a single hierarchy so their is one root directly and every file on the system is located somewhere under it. These use a RAM disk or network shared resource as their root directory.

The system works via mounting a file system where the operating system is told where the files appear in the directory tree. The directory that is accorded the operating system is called the "mount point," for example / media. The / media directory is used as mount point for removable media such as DVDs, CDs, floppy disks or USB drives and exists on many Unix systems. The directory may be empty or may possess subdirectories for mounting individual devices and only the root user may authorize the mounting of the systems.

Unix-like systems often have software and tools that help in the mounting process and provide it with increased efficacy and security. These utilities are provided all the time. In systems like Solaris, for instance, the root system needs to be available as soon as the operating system has booted so that there'd a facility ready for mounting at boot time. Some systems do not mount these file systems at boot time, although oen may need the file after. Some Unix-like systems allow the mounting of certain files upon demand.

Most Unix-like systems also allow removable files via microcomputer platforms such as USB flash drives, DVDs and, and CD ROMs. These systems provide utilities that detect the presence of such a file and mount that medium with least security problems.

Advanced Unix-like systems also provide something called 'supermounting' where the floppy disk (for instance) that has been supermounted can be removed. Linux and Windows both contain this. File security is also implemented by an automounter automatically mounting a file system when reference is made to the file directly on top, which it should be mounted, and preventing others from preempting and affecting.

FAT16, FAT32, and NTFS files

All three files systems - FAT16, FAT32, and NTFS files - work like sectors or batches of clusters that each have certain bytes of information that the CPU is going to process. The sole differnce between each of the file systems - FAT16, FAT32, and NTFS - is that each handles different space and some file systems can handle space more efficiently than others can. Each cluster on a hard disk can store only one file so each stores this file in a different way with all wasting more space as that cluster increases and others being unable to take in more but each wasting space in different ways. Cluster size, in other words, is proportional to wasted space. FAT32 can handle a larger amount of clusters than FAT16 can since the latter only uses 16 binary numbers to count its clusters. FAT 32 in turn remains limited in contradistinction to NTFS since it has a shorter file system overhead.

NTFS allows ACL-based (access control list that is objected attached to an item giving it permission) permission control. It also supports other systems such as hard links, quota tracking, multiple file streams, encryption reparse points, compression, sparse files, quota tracking, indexing, multiple file streams, encryption, and compression. Reparse points include directories that work as mount-points for file systems that include systemlinks, remote storage links, and junctions.)

All three are supported by all versions of Microsoft Window. NTFS is journaled which means that it is not applicable o problems when the system is stopped abruptly since recovery is automatic at the next reboot. On the other hand, the two FATs, being non-journaled, should be examined since they may be subject to problems when the system crashes.

Similarities and Differences: Windows and Linux file system

Windows uses the FAT and NTFS file system with a drive letter code at the user level to distinguish between one disk and another. Most often, Windows uses NTFS. The path C:/Windows represents, for instance the directory Windows that is represented by the letter C. Drive C: / in fact is the most commonly used Drive that Windows usually boots itself from and on which it is installed. Both Linux and Windows also support the concept of hidden files, which are files that are not shown to the user with both tracking them in different ways. Both employ similar case sensitivity with…

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