An Operating System?

• What is an Operating System?
• A program that acts as an intermediary between a user of a computer and the computer hardware.
• What is the purpose of an operating system?
• To provide an environment in which a user can execute programs.
• What are the goals of an Operating System?
• The primary goal of an Operating System is to make the computer system convenient to use.
• The secondary goal is to make the computer system efficient to use.

Computer System Components

• Hardware – provides basic computing resources (CPU, memory, I/O devices).
• Operating system – controls and coordinates the use of the hardware among the various application programs for the various users.
• Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs).
• Users (people, machines, other computers).

Abstract View of System Components

Function of Operating System

• OS as Extended machine
• Computer Architecture shows that computer is made up of chips and wires
• We do not want to program on the bare metal
• Virtual machine creates a hardware abstraction
• Abstract machine can provide hardware independent interfaces
• Increase portability
• Allow greater protection
• Implication is that it is much faster and easier to program with less errors

Function of Operating System

• OS as resource manager
• Coordination and control of limited resources such as memory, disk, network, etc
• Deal with resource conflicts
• Deal with resource fairness
• Make access efficient as possible

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Parts of an Operating System

• No universal agreement on the topic, but most likely
• Memory Management
• IO Management
• CPU Scheduling
• IPC
• MultiTasking/Multiprogramming

(On some Operating System, this functionality is provided by a single program known as the kernel)

• What about?
• File System
• Multimedia Support
• UI (X Windows, MSWin)
• Internet Browser?
• Why would extras be important

Evolution (History) of OS

• First Generation: Punched cards
• Second Generation: Transistors and batch systems.
• Third Generation: (Integrated Circuits)
• Spooling
• Multiprogramming
• Multitasking
• Virtual Memory

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CSE421, Spring 2001

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Spooling

• Stands for Simultaneous Peripheral Operation On-Line
• Takes advantage of disk technology (new at this point)
• Allows for overlap of IO from one job with the computation of another job
• While executing current job
• Read next job from card reader to disk
• Print previous job to printer
• Disk is relegated to the role of a partitioned buffer

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Job pool

• Advent of disk allows for random access
• (Tape and card are sequential)
• Several jobs can be waiting on the disk
• The job pool is a data structure that contains info and points to the jobs on the disk
• We can now have job scheduling to determine the order in which the jobs run so that CPU utilization can increase.

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Multiprogramming

• Memory partitioned into several pieces
• CPU Starts a job
• If the job is waiting for IO, the CPU can switch to another task

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Multitasking (Time-sharing)

• Extension of Multiprogramming
• Need for user interactivity
• Instead of switching jobs when waiting for IO, a timer causes jobs to switch
• User interacts with computer via CRT and keyboard
• Systems have to balance CPU utilization against response time
• Better device management
• Need for file system to allow user to access data and code
• Need to provide user with an “interaction environment”

Virtual Memory

• Programs can be larger than memory
• Program loaded into memory as needed
• Active program and data “swapped” to a disk until needed
• Memory space treated uniformly

Key Events 3^rd Generation

• 1964-1966 IBM/360 and OS/360
• 1964 Dartmouth Time Sharing System
• 1965 DEC PDP-8
• 1965 MIT – Multics Time sharing System
• 1969 – Beginnings of ARPANet
• 1969 - Unix
• 1971 IBM 4001 – Processor on a chip
• 1973 – Ethernet concept Bob Metcalf @ Xerox Parc
• 1974 - Gary Kildall – CP/M OS
• 1974 Zilog Z80 Processor

Key Events (cont)

• 1974 - Edward Roberts, William Yates and Jim Bybee
• MITS Altair 8800.
• $375
• contained 256 bytes of memory
• no keyboard, no display, and no aux storage device.
• 1976 Steve Jobs and Steve Wozniak
• Apple II
• 1977 Commodore PET, Radio Shack TRS_80
• 1979 Unix 3BSD

Fourth Generation : (1980 – 1990)

• Personal Computers
• Computer dedicated to a single user
• IO Devices now consist of keyboards, mice, CGA-VGA displays, small printers
• User convenience and responsiveness
• Can adopt lessons from larger operating systems
• No need for some of the advanced options at the personal level

Key Events 4^th Generation

• 1981 IBM PC (8086)
• 1981 Osborne 1
• 1981 Vic 20
• 1981 Xerox Star Workstation
• 1984 Apple macintosh
• 1984 SunOS
• 1985 C++
• 1985 MSWindows
• 1986 – 386 Chip

Key Events 4^th Generation (cont)

• 1987 OS/2
• 1988 Next Unix Workstations
• 1989 Motif
• 1990 Windows 3,
• 1990 Berners-Lee Prototype for the web

5^th Gen Parallel Systems

• Multiprocessor systems with more than one CPU in close communication.
• Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory.
• Advantages of parallel system:
• Increased throughput
• Economical
• Increased reliability
• graceful degradation
• fail-soft systems

Parallel Systems (Cont.)

• 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

Real-Time Systems

• Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems.
• Well-defined fixed-time constraints (known as deterministic).
• Hard real-time system.
• Secondary storage limited or absent, data stored in short-term memory, or read-only memory (ROM)
• Conflicts with time-sharing systems, not supported by general-purpose operating systems.
• Soft real-time system
• Limited utility in industrial control or robotics
• Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.

Distributed 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 (Cont.)

• Network Operating System
• provides file sharing
• provides communication scheme
• runs independently from other computers on the network
• Distributed Operating System
• less autonomy between computers
• gives the impression there is a single operating system controlling the network.

Why Operating Systems?

• OS for CSE :
• Real world OS is a software engineering problem
• Design of the Virtual/Extended machine
• Development of the Kernel
• OS Usability, Human Factors for OS
• OS for CSE:
• New algorithms to help make OS better, more efficient
• Hypothesis, experiments regarding OS approaches
• OS for anyone else :
• Help to understand better the parts of the OS and how to compare and contrast the various qualities of Operating Systems