introduction, concepts, review & historical perspective processes ◦ synchronization ◦...

Introduction to Operating Systems

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Introduction, concepts, review & historical perspective

Processes◦ Synchronization◦ Scheduling◦ Deadlock

Memory management, address translation, and virtual memory

Operating system management of I/O File systems Distributed systems (as time permits)

CS 1550, cs.pitt.edu (originaly modified by Ethan L. Miller and Scott A. Brandt)Chapter 1

Class outline

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A program that runs on the “raw” hardware and supports◦ Resource Abstraction◦ Resource Sharing

Abstracts and standardizes the interface to the user across different types of hardware◦ Virtual machine hides the messy details which must be

performed Manages the hardware resources

◦ Each program gets time with the resource◦ Each program gets space on the resource

May have potentially conflicting goals:◦ Use hardware efficiently◦ Give maximum performance to each user


What is an operating system?

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Storage pyramid

Goal: really large memory with very low latency◦ Latencies are smaller at the top of the hierarchy◦ Capacities are larger at the bottom of the hierarchy

Solution: move data between levels to create illusion of large memory with low latency

Chapter 1

CS 1550, cs.pitt.edu (originaly modified by Ethan L. Miller and Scott A. Brandt)

Access latency

1 ns

2–5 ns

50 ns

5 ms

50 sec

< 1 KB

1 MB

256 MB

40 GB

> 1 TB

Capacity

Registers

Cache (SRAM)

Main memory (DRAM)

Magnetic disk

Magnetic tapeBetter

Better

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Processes Process: program in

execution◦ Address space (memory) the

program can use◦ State (registers, including

program counter & stack pointer)

OS keeps track of all processes in a process table

Processes can create other processes◦ Process tree tracks these

relationships◦ A is the root of the tree◦ A created three child

processes: B, C, and D◦ C created two child

processes: E and F◦ D created one child process:

GChapter 1

CS 1550, cs.pitt.edu (originaly modified by Ethan L. Miller and Scott A. Brandt)

A

B

E F

C D

G

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Deadlock

Potential deadlock Actual deadlock

Scheduling the processor among all ready processes

The goal is to achieve: ◦ High processor utilization◦ High throughput

number of processes completed per of unit time◦ Low response time

time elapsed from the submission of a request until the first response is produced

CPU Scheduling

Long-term: which process to admit? Medium-term: which process to swap in or out? Short-term: which ready process to execute next?

Classification of Scheduling Activity

Queuing Diagram for Scheduling

The selection function determines which ready process is selected next for execution

The decision mode specifies the instants in time the selection function is exercised◦ Nonpreemptive

Once a process is in the running state, it will continue until it terminates or blocks for an I/O

◦ Preemptive Currently running process may be interrupted and

moved to the Ready state by the OS Prevents one process from monopolizing the

processor

Characterization of Scheduling Policies

First-Come, First-Served Scheduling Shortest-Job-First Scheduling

◦ Also referred to as Shortest Process Next Round-Robin Scheduling

Scheduling Algorithms

Process Mix Example

ProcessArriv

alTime

ServiceTime

1

2

3

4

5

0

2

4

6

8

3

6

4

5

2

Service time = total processor time needed in one (CPU-I/O) cycleJobs with long service time are CPU-bound jobs and are referredto as “long jobs”

Selection function: the process that has been waiting the longest in the ready queue (hence, FCFS)

Decision mode: non-preemptive◦ a process runs until it blocks for an I/O

First Come First Served (FCFS)

Selection function: the process with the shortest expected CPU burst time◦ I/O-bound processes will be selected first

Decision mode: non-preemptive The required processing time, i.e., the CPU

burst time, must be estimated for each process

Shortest Job First (Shortest Process Next)

Selection function: same as FCFS Decision mode: preemptive

a process is allowed to run until the time slice period (quantum, typically from 10 to 100 ms) has expired

a clock interrupt occurs and the running process is put on the ready queue

Round-Robin

Memory Management

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Subdividing memory to accommodate multiple processes

Memory needs to be allocated to ensure a reasonable supply of ready processes to consume available processor time

Memory Management

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Equal-size partitions◦ Any process whose size is less than or equal to

the partition size can be loaded into an available partition

◦ If all partitions are full, the operating system can swap a process out of a partition

◦ A program may not fit in a partition. The programmer must design the program with overlays

Fixed Partitioning

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Main memory use is inefficient. Any program, no matter how small, occupies an entire partition. This is called internal fragmentation.

Fixed Partitioning

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Base register◦ Starting address for the process

Bounds register◦ Ending location of the process

These values are set when the process is loaded or when the process is swapped in

Registers Used during Execution

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Partition memory into small equal fixed-size chunks and divide each process into the same size chunks

The chunks of a process are called pages and chunks of memory are called frames

Operating system maintains a page table for each process◦Contains the frame location for each page in

the process◦Memory address consist of a page number

and offset within the page

Paging

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Assignment of Process Pages to Free Frames

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Assignment of Process Pages to Free Frames

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Page Tables for Example

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All segments of all programs do not have to be of the same length

There is a maximum segment length Addressing consist of two parts - a segment

number and an offset Since segments are not equal,

segmentation is similar to dynamic partitioning

Segmentation

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Logical◦ Reference to a memory location independent of

the current assignment of data to memory◦ Translation must be made to the physical

address Relative

◦ Address expressed as a location relative to some known point

Physical◦ The absolute address or actual location in main

memory

Addresses

Symmetric multiprocessing (SMP)◦ Each processor runs an identical copy of the

operating system.◦ Many processes can run at once without

performance deterioration.◦ Most modern operating systems support SMP

Asymmetric multiprocessing◦ Each processor is assigned a specific task;

master processor schedules and allocates work to slave processors.

◦ More common in extremely large systems

Parallel Systems

Distribute the computation among several physical processors.

Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines.

Advantages of distributed systems.◦ Resources Sharing ◦ Computation speed up – load sharing ◦ Reliability◦ Communications

Distributed Systems

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Definition:Tightly-coupled CPUs that do not share memory

Also known as ◦cluster computers◦clusters of workstations (COWs)

CS 1550, cs.pitt.edu (originaly modified from MOS2 slides by A.

Tanenbaum)

Multicomputers

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Interconnection topologies(a) single switch(b) ring(c) grid

(d) double torus(e) cube(f) hypercubeCS 1550, cs.pitt.edu (originaly

modified from MOS2 slides by A. Tanenbaum)

Multicomputer Hardware

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