Tugas Orkom Rangkum perkuliahan 6

 ORGANISASI &ARSITEKTUR KOMPUTER

PERTEMUAN KE-6

Dukungan Sistem Operasi

TIK:

Objectives and Functions

Convenience

Making the computer easier to use

Efficiency

Allowing better use of computer resources

Operating System Services

Program creation

Program execution

Access to I/O devices

Controlled access to files

System access

Error detection and response

Accounting

Types of Operating System

Interactive

Batch

Single program (Uni-programming)

Multi-programming (Multi-tasking)

Early Systems

Late 1940s to mid 1950s

No Operating System

Programs interact directly with hardware

Two main problems:

Scheduling

Setup time

Simple Batch Systems

Resident Monitor program

Users submit jobs to operator

Operator batches jobs

Monitor controls sequence of events to process batch

When one job is finished, control returns to Monitor which

reads next job

Monitor handles scheduling

Desirable Hardware Features

Memory protection

To protect the Monitor

Timer

To prevent a job monopolizing the system

Privileged instructions

Only executed by Monitor

e.g. I/O

Interrupts

Allows for relinquishing and regaining control

Multi-programmed Batch Systems

I/O devices very slow

When one program is waiting for I/O, another can use the CPU

Time Sharing Systems

Allow users to interact directly with the computer

i.e. Interactive

Multi-programming allows a number of users to interact with

the computer

Scheduling

Key to multi-programming

Long term

Medium term

Short term

I/O

Long Term Scheduling

Determines which programs are submitted for processing

i.e. controls the degree of multi-programming

Once submitted, a job becomes a process for the short term

scheduler

(or it becomes a swapped out job for the medium term

scheduler)

Medium Term Scheduling

Part of the swapping function (later…)

Usually based on the need to manage multi-programming

If no virtual memory, memory management is also an issue

Short Term Scheduler

Dispatcher

Fine grained decisions of which job to execute next

i.e. which job actually gets to use the processor in the next time

slot

Process Control Block

Identifier

State

Priority

Program counter

Memory pointers

Context data

I/O status

Accounting information

Memory Management

Uni-program

Memory split into two

One for Operating System (monitor)

One for currently executing program

Multi-program

“User” part is sub-divided and shared among active processes

Swapping

Problem: I/O is so slow compared with CPU that even in

multi-programming system, CPU can be idle most of the time

Solutions:

Increase main memory

Expensive

Leads to larger programs

Swapping

What is Swapping?

Long term queue of processes stored on disk

Processes “swapped” in as space becomes available

As a process completes it is moved out of main memory

If none of the processes in memory are ready (i.e. all I/O

blocked)

Swap out a blocked process to intermediate queue

Swap in a ready process or a new process

But swapping is an I/O process...

Partitioning

Splitting memory into sections to allocate to processes

(including Operating System)

Fixed-sized partitions

May not be equal size

Process is fitted into smallest hole that will take it (best fit)

Some wasted memory

Leads to variable sized partitions

Variable Sized Partitions (1)

Allocate exactly the required memory to a process

This leads to a hole at the end of memory, too small to use

Only one small hole - less waste

When all processes are blocked, swap out a process and bring

in another

New process may be smaller than swapped out process

Another hole

Variable Sized Partitions (2)

Eventually have lots of holes (fragmentation)

Solutions:

Coalesce - Join adjacent holes into one large hole

Compaction - From time to time go through memory and move all

hole into one free block (c.f. disk de-fragmentation)

Relocation

No guarantee that process will load into the same place in

memory

Instructions contain addresses

Locations of data

Addresses for instructions (branching)

Logical address - relative to beginning of program

Physical address - actual location in memory (this time)

Automatic conversion using base address

Paging

Split memory into equal sized, small chunks -page frames

Split programs (processes) into equal sized small chunks -

pages

Allocate the required number page frames to a process

Operating System maintains list of free frames

A process does not require contiguous page frames

Use page table to keep track

Virtual Memory

Demand paging

Do not require all pages of a process in memory

Bring in pages as required

Page fault

Required page is not in memory

Operating System must swap in required page

May need to swap out a page to make space

Select page to throw out based on recent history

Thrashing

Too many processes in too little memory

Operating System spends all its time swapping

Little or no real work is done

Disk light is on all the time

Solutions

Good page replacement algorithms

Reduce number of processes running

Fit more memory

Bonus

We do not need all of a process in memory for it to run

We can swap in pages as required

So - we can now run processes that are bigger than total

memory available!

Main memory is called real memory

User/programmer sees much bigger memory - virtual memory

Segmentation

Paging is not (usually) visible to the programmer

Segmentation is visible to the programmer

Usually different segments allocated to program and data

May be a number of program and data segments

Advantages of Segmentation

Simplifies handling of growing data structures

Allows programs to be altered and recompiled independently,

without re-linking and re-loading

Lends itself to sharing among processes

Lends itself to protection

Some systems combine segmentation with paging

Required Reading

Stallings chapter 7

Stallings, W. Operating Systems, Internals and Design

Principles, Prentice Hall 1998

Loads of Web sites on Operating Systems

NAMA : M. ANANG MA'RUF

KELAS: TEKNIK INFORMATIKA (B)

NIM     : 23420003