Chapter 8 Operating System Support Pokok-Pokok Penting Sistem Operasi merupakan s/w yg mengontrol eksekusi program-program pada sebuah prosesor dan mengatur sumber daya prosesornya. Salah satu fungsi paling utama Sistem Operasi adalah penjadwalan proses-proses Fungsi sistem operasi penting lainnya adalah manajemen memori.

Chapter 8 Operating System Support Tujuan dan Fungsi Sistem Operasi Kenyamanan : dengan sistem operasi membuat komputer lebih mudah untuk digunakan Efisiensi: memungkinkan sumber daya sistem komputer dapat digunakan dgn cara yang efisien.

1. Sebagai extended machine FUNGSI SISTEM OPERASI 1. Sebagai extended machine Menyembunyikan kompleksitas pemrograman hardware dari programmer atau user Menyajikan fasilitas yang lebih mudah untuk menggunakan hardware 2. Sebagai resource manager Mengatur dan mengefisienkan penggunaan sumber daya komputer Masing-masing program mendapatkan waktu dan space terhadap sumber daya

Layers and Views of a Computer System

Komponen utama sistem komputer

Penempatan Sistem Operasi pada Sistem Komputer

Operating System Services (Layanan-layanan Sistem Operasi Pembuatan Program Biasanya dlm bentuk utiliti spt: editor, debugger untuk membantu programmer Eksekusi Program Menaruh instruksi dan data ke main memory Akses ke perangkat I/O Sistem operasi mengatasi masalah detail operasional perangkat I/O, shg pemrogram dpt menggunakan dlm bentuk yg lebih sederhana. Controlled access to files Sistem multi user, o/s menyediakan mekanisme perlindungan untuk akses ke file System access Perlindungan sumber daya dan data Error detection and response Accounting o/s mengumpulkan statistik pemakaian untuk berbagai sumber daya, yg berguna untuk peningkatan kinerja

O/S as a Resource Manager (Sistem Operasi sebagai Manajer Sumber Daya)

Types of Operating System ( Jenis-jenis Sistem Opersai ) Interactive User berinteraksi secara langsung dgn komputer Batch Program user ditampung bersama-sama dgn user yg lainnya, dan kemudian disampaikan ke operator komputer. (sekarang jarang) Single program (Uni-programming) Mengerjakan satu program setiap saat Multi-programming (Multi-tasking) Menjaga agar prosesor sibuk setiap saat, dgn mengerjakan program lebih dari satu setiap saat Beberapa program di-load ke main memory dan prosesor beralih dari satu program ke program yang lainnya.

MonoProgrammming, MultiProgramming, ParalelProgramming job Selesai 3 2 1 T0 T1 T2 T3 waktu Mono Programming

MonoProgrammming, MultiProgramming, ParalelProgramming job 3 2 1 waktu T0 Multi Programming

MonoProgrammming, MultiProgramming, ParalelProgramming 3 2 1 waktu T0 Paralel Programming

A B MonoProgramming

MonoProgramming

MonoProgramming

MonoProgramming

MonoProgramming

MonoProgramming

MultiProgramming

MultiProgramming

Quantum MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

MultiProgramming

Paralel Programming

Paralel Programming

Paralel Programming

Paralel Programming

Paralel Programming

Early Systems (sistem-sistem awal) Akhir 1940 s/d pertengahan 1950 Tidak menggunakan Sistem Operasi Program berinteraksi langsung dgn hardware Dua masalah utama: Scheduling (penjadwalan) Mendaftar menggunakan prosesor dlm waktu kelipatan 30 menit, jika ada error => berhenti sebelum dpt memecahkan masalah. Setup time (Waktu setup) Pemasangan pita atau punch card, dll

Simple Batch Systems (Sistem Batch Sederhana) Simple batch system disebut juga dgn: Monitor Resident Monitor program (lihat gbr slide berikutnya) Users menyerahkan jobs ke operator Operator melakukan batches jobs => melalui perangkat input yg bisa diakses oleh Monitor Monitor mengontrol urutan peristiwa Bila satu job sdh selesai, control dikembalikan ke Monitor, dan Monitor akan membaca job berikutnya Monitor handles scheduling

Batch System

Memory Layout for Resident Monitor

Job Control Language (JCL) Bahasa pemrogram khusus yg digunakan untuk memberikan instruksi ke Monitor Contoh: e.g. $JOB $FTN //memuat kompiler ... Some Fortran instructions $LOAD //kompilasi $RUN ... Some data $END

Desirable Hardware Features ( Fitur-fitur perangkat keras yg dibutuhkan) Memory protection To protect the Monitor (program user tdk boleh merubah area memori monitor) Timer / pengatur waktu To prevent a job monopolizing the system Jika pengatur waktu berakhir, terjadi interrupt dan kontrol kembali ke monitor Privileged instructions / istruksi-instruksi istimewa Only executed by Monitor e.g. I/O Interrupts Memberikan o/s lebih fleksibel dlm melepaskan kontrol ke program pengguna dan mendapatkan kembali kontrol dari pengguna.

Multi-programmed Batch Systems I/O devices very slow When one program is waiting for I/O, another can use the CPU Single Program

Multi-Programming with Two Programs

Multi-Programming with Three Programs

Utilization

Time Sharing Systems (Sistem berbagi waktu) Sistem Multiprogramming: Memaksimalkan penggunaan prossor Perintah dari Jobs Time sharing system: Meminimumkan waktu respon Perintah dimasukkan dari terminal

Scheduling Long term (penjadwalan Jangka Panjang) Medium term (penjadwalan Jangka Menengah) Short term (penjadwalan jangka pendek) I/O (penjadwalan I/O)

Long Term Scheduling Menentukan program yang akan diproses / submitted Mengontrol degree of multi-programming Sekali di-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 Swapping-in & Swapping-out

Short Term Scheduler Disebut juga = Dispatcher Fine grained decisions of which job to execute next

Process States

Process Control Block Isi dari PCB : Identifier : Setiap proses yg sedang berjalan mempunyai Identifier yg unik State Priority Program counter Memory pointers : Lokasi awal dan akhir dari proses di memori Context data : Data pada register pada saat program dieksekusi I/O status : Permintaan I/O yg belum dipenuhi, I/O yg ditugaskan pd proses ini, daftar file yg di open. Accounting information : Jumlah waktu prosesor dan waktu yg digunakan.

PCB Diagram

Key Elements of O/S (Elemen-elemen penting sistem operasi untuk multiprogramming)

Process Scheduling

Memory Management Uni-program Multi-program Memori dibagi menjadi dua Satu untuk Operating System (monitor) Satunya lagi untuk mengeksekusi 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 Program kecenderungannya bertambah besar 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 (dipindahkan dari memori utama) 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

Fixed Partitioning

Variable Sized Partitions (1) Allocate exactly the required memory to a process 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)

Effect of Dynamic Partitioning

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, =>page frames Split programs (processes) into equal sized => 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

Logical and Physical Addresses - Paging

Virtual Memory Demand paging Page fault 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

Page Table Structure

Translation Lookaside Buffer Every virtual memory reference causes two physical memory access Fetch page table entry Fetch data Use special cache for page table TLB

TLB Operation

TLB and Cache Operation

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