Secondary Disk Scheduling Management

Published Date: 02 Nov 2017

Windows 8 vs Ubuntu

The operating system of Window fee for Window 8 pro (32bit) version totally is $39 to $69 for an upgrade from Windows 7. By the way Ubuntu is open source operating system, that means is free for using. The 32 bit and 64 bit CPU architecture are supported in Windows 8 and Ubuntu. But for the Ubuntu 12.10 also supports by ARM and PPC. The minimum RAM of requirement between Windows 8 PC is different from 1GB to 2GB, where in Ubuntu it’s only 512MB. For the hard disk space is required in Windows 8 in 20GB compared with Ubuntu 5 GB. Ubuntu12.10 operating system comes with advanced productivity software included in the form of Libre Office and has graphic tools. But for Window 8 are non-existent.

Below is the figure of Memory usage for Ubuntu 12.10 and Windows 8.

D:\Users\Sherman Heng\Desktop\Screenshot from 2013-02-20 08_14_15.pngwindows_8_will_have_improved_memory_management

Memory usage between Ubuntu 12.10 and Windows 8.

From bot h figure above, it shows that Ubuntu 12.10 is uses around to operate which is around 433.4 MB out of 2048 MB while Window 8 uses which is around 281 MB out of 1014.1MB.

Process Control Management

Threads 

Process in the Ubuntu 12.10 operating system is a unit work with unique which progresses in a system begins. Thus, this process will go through about a small series such as same internal representation for processes and threads. A thread is a new process it to sharing the same address space as its parent and thread is created by the clone system call when a distinction is to made.

• fork – is to creates a new process with its own entirely with new process context.

• clone – is to creates a new process with its own identity, but that is only allowed to share the data structures of its parent.

Processes states

In Ubuntu processes is created with a fork until it has completed its job and disappears from the process table, it goes through like this many different states. In addition, the state a process it will changes many times during its "States." These changes can occur, for example, the process will ask for a resource that is currently not available when the process is making a system call, it is someone else's turn to run, an interrupt occurs. A process is active while a program is passive. The operating system it will keeps track of processes when using a process table.

Below the picture was shown the process state details and diagram of process state.

Ready - The process is competing for the processor, but another process is will currently being executed.

In Ubuntu 12.10, there have many processes in memory need to execute it, but there possible make one processor to execute one process at a same time. Other processes have to wait and prepare for the allocation from the processor, it called ready state.

Execution - The process is active or running or being executed by processor.

Suspend - The process is waiting for an external event.

Stopped - The process has been suspended by an external process.

Zombie - The process has finished executed, but it is still references in the system.

Terminated -This process is complete execution.

Figure : Linus Process

Process Control Block

A Process Ubuntu 12.10 operating system is represented a data structure in the core of operating system and it also related the data records of process. It called Process Control Block, process control block which are (PCB) is to contain information associated with important information about the specific process including:

Process State - The information about the process state; ready, running, blocked, terminated, new.

Process ID – Is a process to assign an unique of identification number, when entered into the system.

Program Counter – This program counter is the information of Ubuntu about the contents of the CPU registers.

CPU Registers - Is to hold the processed of CPU Registers processed of the result with the calculations or addresses pointing to the memory locations of desired data.

CPU-Scheduling information – The Ubuntu 12.10 operating system is important include in scheduling such as information, pointers to scheduling queues, scheduling parameters, and process priority.

Memory-Management information - In this memory management information is depending about the operating system, it included the page tables, segment tables, or value of the base and limit registers.

Accounting information - Is the information about included the process number, CPU used by the process time limits etc.

I/O Status information - This I/O status information is Storage indicators, refers to the file table record which are allocated to processes it.

Process Control Block

Process Scheduling

Process Scheduling is the process a CPU scheduler is tasked with choosing which process to run first from the ready queue. The running of processes is managed by the main part of operating system that is scheduler. For the objective of multiprogramming is starting to process at all the times, to maximize CPU utilization.

Ubuntu 12.10 uses two separate process-scheduling algorithms:

One is time-sharing for fair, preemptive scheduling among multiple processes; the other is designed for real-time tasks.

Real-time algorithms are also supported, for tasks where absolute priorities are more important than fairness.

First in First out (SCHED_FIFO)

First in First out is the simplest CPU scheduling algorithm of first-served scheduling (FCFS) algorithm in Ubuntu implements.

FCFS is very simple - Just like a FIFO queue, normally the customers is waiting in line to buy movie ticket at the cinema or to see the doctor. Unfortunately, the FCFS can yield longer average wait times for each people, some particularly if the first process to get there takes a long time. For example, consider the following three processes:

Process

Burst Time

P1

24

P2

3

P3

3

Round robin (SCHED_RR)

The process will leave the CPU if it takes a running time out, call ‘quantum time’.

The round-robin (RR) scheduling is designed especially for time sharing systems.

a time quantum / time slice is defined for each process

the ready queue is treated as a circular queue

A context switch will be executed and the process will be put at the tail of the ready queue.

C:\Users\user\Desktop\RR.JPG

SCHED_OTHER: Tasks are normal user tasks (default)

SCHED_FIFO: Task that running with this policy will never be preempted. It is a real-time policy.

SCHED_RR: This is another real-time policy, but the task will leave the CPU if there is another real-time task in the run queue.

Deadlock Management

Ubuntu 12.10 in deadlock can occurs in many situations and also it may not be handled. Deadlock it can be happen on any kind of shared resource and with more than two processes think of three or more then processes in a circle. Linux Kernel ignores deadlocks because it happen so infrequently that the cost to manage monitoring and resolution far exceeds the benefit of available at all that time, the process it able to enters a waiting state and the process requests resources. Deadlock is defined as the deadlocked if each process is set waiting for an event and permanent blocking of a set of processes that compete for system resources. In addition, a deadlock situation arises if two of the following conditions are held simultaneously in the Ubuntu operating system:

Mutual exclusion

- Only can one process can use a resource ate time

- The mutual-exclusion condition must be holding for a non-sharable resources example printer.

- In Ubuntu 12.10 we cannot prevent deadlocks by denying the mutual-exclusion condition, because some of the resources are intrinsically non-sharable.

Hold and wait

- A process can able to continue to hold a resource while once is waiting for other resource.

- A protocol that can be used required for each process to request and able be allocated all its resources before it begins an implementation.

No preemption condition

- No resource can forcibly be removed from a process holding it.

- Resources previously granted is cannot be forcibly by taken away from a process. They must be explicitly released by the process holding them.

Circular Wait condition

All the process can be able to demand resources only in an increasing order of enumeration.

If these both protocols are used, then the circular-wait condition is cannot be hold.

In Ubuntu 12.10 the way to overcome deadlock situations we have:

Deadlock handling strategies:

Just ignore the problem altogether(The Ostrich algorithm)

Deadlock prevention – Deadlock prevention is a condition imposition to remove any of possibility of deadlock occurrence, sometimes it can be clean solution or cause poor resources utilization.

Deadlock avoidance - Ubuntu 12.10 in deadlock avoidance is less stringent conditioning otherwise is better resources utilization and does not precondition the system to remove all deadlock possibility.

Deadlock detection - is a systems that allow deadlocks to occur and identify the deadlocked process, resource or to clear deadlock.

Deadlock prevention - It is to removing no preemption condition may be hard to ignore because each process should have at least few resources to perform a given task.

Deadlock recovery – Deadlock recovery of Ubuntu is a methods used to clear deadlock of process flush and partial or all previous work done by these processes being lost.

Banker's Algorithm

The Ubuntu 12.10 in Banker's algorithm is running by the operating system which a process requests resources. Other than that, the algorithm prevents deadlock by denying or postponing in the request of determines that accepting the request it could put the system in an unsafe state or it will happen where deadlock could occur. When the time new process is enters into a system, it must be declaring the full of maximum number instances of each resource type that may not exceed the total number of resources in the system.

• It a state of the system of current allocation of resources to process

• It a safe state where there in the least of the one sequence that does not show the result in deadlock.

• Unsafe state is a state of not safe

Memory management

Memory management is a general term which describes how operating systems handle the RAM available in a system. The memory management provided by Ubuntu 12.10 has clearly improved by nowadays compared to previous version of Ubuntu operating system. Ubuntu 12.10 does the memory manager offers the system services to assign and free virtual memory implements provides a core set of services such as memory mapped files, copy-on-write memory, large memory support, and locking pages in physical memory. For the memory is divided into two categories which are physical memory and the logical memory.

The Logical memory is an operating system of the computer has to assign to more of the one physical memory blocks from the RAM for a particular process. In this case the process will have more than one physical address and this will cause problems in situations where paging is done. The physical memory is the memory available in Random Access Memory (RAM) and is further divided into much memory with a physical address which is used for loading application.

Logical memory

Ubuntu 12.10 separates physical memory into three different zones:

Zone_DMA is the first section that consist 16MB of physical memory which is for the Direct Access Memory able page. After the Zone DMA is Zone_NORMAL which are first 16...896MB of physical memory that is normally accessible. If the system has more than 896MB of memory, then it will be allocated as Zone_HIGHMEM.

Virtual Memory

The Virtual Memory management system is where a logical memory area that is generated by the CPU and the most important part of an operating system. From the beginning of the computer operations there has been a need for more memory than the exciting physical memory in a computer. It creates pages of virtual memory for the manages the loading of each pages from disk or their swapping back out to disk as required. Virtual memory is their most successful method. Virtual memory possible to makes the computer appear have more memory than compared with physical memory.

Virtual Memory

Swap-In and Swap-Out

Swap –in Swap- out is use when the physical memory using in your computer by the time to running processes yet an additional the demand for memory resources exist. Swap space is the important part of the Virtual Memory of user’s machine on a hard drive, which is make a combination of accessible physical memory (RAM) and swap space. Ubuntu 12.10 in Swap space by using with the amount of physical memory (RAM) is totally full holds memory pages that are inactive. Swap space is using by the system when needs more memory resources and the RAM is full, the memory are moved to the swap space. Swap space can be swap partition which are (recommended), a swap file, or combination of swap partitions and swap files. When the pages are swapping, swap space are needed by the physical memory again, then will happen swapped backed into the physical memory again. These operations are called swapping out and swapping in, respectively. Swap equal to 2x physical RAM for up to 2 GB of physical RAM, for an additional is 1x physical RAM for 2 GB, but never less than 32 MB.

Swap-In and Swap-Out

Secondary Disk Scheduling Management

The secondary disk also known as secondary storage in computer system, where the place data in held in an electromagnetic or optical form for access by a computer" (Rouse, 2005). A hard disk drive is a collection of plates called platters. It a large data storage device to stores more data and information from the hard disk component. Secondary disk scheduling helps to operate the hardware efficiently which is faster access time and increase disk band width Invalid source specified. Thus, disk scheduling system are using algorithm to improve the access time and increase disk bandwidth.

There are two objectives for any disk scheduling algorithm:

Maximize the throughput - the average number of requests satisfied per time unit.

Minimize the response time - the average time that a request must wait before it is satisfied.

http://users.cs.cf.ac.uk/O.F.Rana/os/lectureos11/img12.gif

FS i DISK SCHEDULING Served) FCFS (First Come, First Served) FCFS (First Come, First

FCFS (First Come, First Served) FCFS (First Come, First Served)

Some of the disks scheduling algorithms are explained below:

First Come-First Serve (FCFS) - To requests arrive based on order which first to arrive.

Shortest Seek Time First (SSTF) –To requests are serviced based on which request is getting near to the current head position of the hard disk.

SCAN – To request arrives of the head serviced first, the request will need to wait till the arm moves back.

Circular SCAN (C-SCAN) –It starts from the head moves from one end of the disk to the other service request then the arm moves back without servicing any request

C-LOOK - Starts from the current head and moves towards to the end.

Round-Robin Scheduling

The round-robin (RR) scheduling algorithm actually is for advanced designed for the time-sharing between the systems. It is similar to FCFS scheduling, but pre-emption is added to switch between processes.

Implement RR scheduling,

• Similar to keep the ready queue as a FIFO queue of processes.

• Similar to the new processes are added to the tail of the ready queue.

Round Robin scheduling

Secondary Disk Scheduling Management

For the Ubuntu 12.10 secondary disk scheduling management will able to allow user to partition to the disk with their own interest or it only to create default partition. The disk manager shows that partitions are available for each and all the storage disk. Which only the file system that uses for those partitions, path for access that device, size of that device and the free space available in that device and status about that space whether the user can access that device or not.

This is the following diagram shows a screenshot of disk manager and its properties.