Review OS : Chapter 2

1. definition of term (4)- eg scheduling ...

Penjadualan Kerja (Penjadualan jangka panjang) - LTS

Keputusan untuk menambah kepada kumpulan proses ke

      dilaksanakan (proses aktif)

Dilakukan apabila proses baru dibuat



Penjadualan jangka sederhana - MTS

Keputusan untuk menambah bilangan proses yang ada

     sebahagian atau sepenuhnya dalam memori utama (kini aktif)

sebahagian daripada fungsi swap



Penjadualan CPU (Penjadualan jangka pendek) - STS

Keputusan mengenai proses yang sedia ada (proses siap) akan dilaksanakan oleh pemproses



Penjadualan I / O - (akan dibincangkan di bab I / O)

Keputusan mengenai permintaan I / O yang menunggu proses itu akan ditangani oleh peranti I / O yang tersedia

2. draw the process switching and dispatcher

dispatcher

Dispatcher –
Dispatcher is a special program which comes into play after scheduler. When scheduler completed its job of selecting a process, then after it is the dispatcher which takes that process to the desired state/queue. The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler. This function involves the following:

• Switching context
• Switching to user mode
• Jumping to proper location in user program to restart that program

Difference between the Scheduler and Dispatcher –
Consider a situation, where various process residing in ready queue and waiting for execution. But CPU can’t execute all the process of ready queue simultaneously, operating system have to choose a particular process on the basis of scheduling algorithm used. So, this procedure of selecting a process among various process is done by scheduler. Now here the task of scheduler completed. Now dispatcher comes into picture as scheduler have decide a process for execution, it is dispatcher who takes that process from ready queue to the running status, or you can say that providing CPU to that process is the task of dispatcher.

Example –
There are 4 process in ready queue, i.e., P1, P2, P3, P4; They all are arrived at t0, t1, t2, t3 respectively. First in First out scheduling algorithm is used. So, scheduler decided that first of all P1 has came, so this is to be executed first. Now dispatcher takes P1 to the running state.

Schedulers are special system software which handle process scheduling in various ways. Their main task is to select the jobs to be submitted into the system and to decide which process to run. There are three types of Scheduler:

Long term (job) scheduler – Due to smaller size of main memory initially all program are stored in secondary memory. When they are stored or loaded in main memory they are called process. This is decision of long term scheduler that how many process will stay in ready queue. Hence, in simple words long term scheduler decides degree of multi-programming of system.


Medium term scheduler – Most often, a running process needs I/O operation which doesn’t requires CPU. Hence during execution of a process when a I/O operation is required then operating system sends that process from running queue to blocked queue. When a process completes its I/O operation then it should again shifted to ready queue. ALL these decisions are taken by medium term scheduler. Medium-term scheduling is a part of swapping.


Short term (CPU) scheduler – When there are lots of processes in main memory initially all are present in ready queue. Among all of the process a single process is to be selected for execution. This decision is handled by short term scheduler.

Lets have a look on the figure given below. It may make more clear view for you.

PROPERTIES
DISPATCHER
SCHEDULER

Definition:
Dispatcher is a module that gives control of CPU to the process selected by short term scheduler
Scheduler is something which selects a process among various processes
Types:
There are no diifrent types in dispatcher.It is just a code segment.
There are 3 types of scheduler i.e. Long-term, Short-term, Medium-term

Dependency:
Working of dispatcher is dependednt on scheduler.Means dispatcher have to wait untill scheduler selects a process.
Scheduler works idependently.It works immediately when needed
Algorithm:
Dispatcher has no specific algorithm for its implementation
Scheduler works on various algorithm such as FCFS, SJF, RR etc.
Time Taken:
The time taken by dispatcher is called dispatch latency.
TIme taken by scheduler is usually negligible.Hence we neglect it.
Functions:
Dispatcher is also responsible for:Context Switching, Switch to user mode, Jumping to proper location when process again restarted
The only work of scheduler is selection of processes.

3. given a program, determine whether a line of code is CPU bound or I/O bound /diberi program, tentukan sama ada garisan kod adalah terikat CPU atau I / O terikat

CPU Bound means the rate at which process progresses is limited by the speed of the CPU. A task that performs calculations on a small set of numbers, for example multiplying small matrices, is likely to be CPU bound.




Bound CPU bermaksud kadar di mana proses berlangsung adalah terhad oleh kelajuan CPU. Satu tugas yang melakukan pengiraan pada set kecil nombor, contohnya mengalikan matriks kecil, mungkin menjadi terikat CPU.




I/O Bound means the rate at which a process progresses is limited by the speed of the I/O subsystem. A task that processes data from disk, for example, counting the number of lines in a file is likely to be I/O bound.




I / O Bound bermaksud kadar di mana proses berlangsung terhad oleh kelajuan subsistem I / O. Satu tugas yang memproses data dari cakera, sebagai contoh, mengira bilangan garisan dalam fail mungkin I / O terikat.







-------------------

CPU Bound means the rate at which process progresses is limited by the speed of the CPU.

A task that performs calculations on a small set of numbers, for example multiplying small matrices, is likely to be CPU bound.
A program is CPU bound if it would go faster if the CPU were faster.



Bound CPU bermaksud kadar di mana proses berlangsung adalah terhad oleh kelajuan CPU.
Satu tugas yang melakukan pengiraan pada set kecil nombor, contohnya mengalikan matriks kecil, mungkin menjadi terikat CPU.
Program adalah terikat CPU jika ia akan lebih cepat jika CPU lebih cepat.







I/O Bound means the rate at which a process progresses is limited by the speed of the I/O subsystem.

A task that processes data from disk, for example, counting the number of lines in a file is likely to be I/O bound.
A program is I/O bound if it would go faster if the I/O subsystem was faster.

I / O Bound bermaksud kadar di mana proses berlangsung terhad oleh kelajuan subsistem I / O.
Satu tugas yang memproses data dari cakera, sebagai contoh, mengira bilangan garisan dalam fail mungkin I / O terikat.
Satu program adalah I / O terikat jika ia akan berjalan lebih cepat jika subsistem I / O lebih cepat.

4. state model

https://t4tutorials.com/five-state-process-model-in-operating-systems/

5. given a code, draw the process tree

6. On scheduling, given a table of job, calculate AWT and ATT for different scheduling policy

waiting time P1 = 6 ; P2
































*** too specific questions not mention here
** in general - you have to read and digest Chapter 2