Contact Information

1
Contact Information

• Office 225 Neville Hall
• Office Hours Monday and Wednesday 1200-100
• E-Main dickens_at_umcs.maine.edu
• Phone [phone]
• Textbook Tanenbaum, Modern Operating Systems
  (2nd edition)
• URL http//umcs.maine.edu/dickens/COS431/COS431.
  html

2
Introduction

• Chapter 1

1.1 What is an operating system 1.2 History of
operating systems 1.3 The operating system
zoo 1.4 Computer hardware review 1.5 Operating
system concepts 1.6 System calls 1.7 Operating
system structure
3
Introduction

• A computer system consists of
• hardware
• system programs
• application programs

4
System Components

• Hardware
• Physical Devices
• Memory, CPU, I/O devices.
• Microarchitecture Executes machine-level
  instructions. Hardware or firmware.
• Machine language Hardware and instructions
  visible to an assembly language program.

5
Introduction

• Operating System
• Hides complexity of hardware and provides
  simplified set of instructions.

6
Introduction

• System programs
• Generally execute in user mode.
• Command interpreter (shell), compilers, editors,
  ..

7
So What is an Operating System?

• It is an extended machine
• Hides the messy details which must be performed
• Presents user with a virtual machine, easier to
  use
• Dont want to program I/O devices, handle
  interrupts, etc.
• It is a resource manager (and scheduler)
• Each program gets time with the resource
• E.g., CPU, I/O devices, memory
• Each program gets space on the resource
• E.g., Disk space.

8
History of Operating Systems

• First generation 1945 - 1955
• vacuum tubes, plug boards
• Scheduling algorithm was a signup sheet.
• Second generation 1955 1965
• Operator loading in programs from card deck one
  at a time.
• Led to batch systems

9

• Early batch system
• bring cards to 1401
• read cards to tape
• put tape on 7094 which does computing
• put tape on 1401 which prints output

10
History of Operating Systems (3)

• Structure of a typical FMS job 2nd generation

11
Early Operating Systems

• Automatic job sequencing automatically
  transfers control from one job to another. First
  rudimentary operating system.
• Resident monitor
• initial control in monitor
• control transfers to job
• when job completes control transfers pack to
  monitor

12
Memory Layout for a Simple Batch System
13

• Third generation 1965 1980
• Machines were very expensive and CPU frequently
  idle. Led to multiprogramming.

14

• Multiprogramming system
• three jobs in memory 3rd generation

15
Multiprogramming Batch Systems
Solution Multiplex CPU between multiple jobs.
16
OS Features Needed for Multiprogramming

• Use of disk space to hold jobs not in system.
• Job scheduling Choose jobs to bring into memory.
• Memory management the system must allocate the
  memory to several jobs.
• CPU scheduling the system must choose among
  several jobs ready to run.
• Allocation of devices.

17
Time-Sharing SystemsInteractive Computing

• The CPU is multiplexed among several jobs that
  are kept in memory and on disk (the CPU is
  allocated to a job only if the job is in memory).
• A job swapped in and out of memory to the disk.
• On-line communication between the user and the
  system is provided when the operating system
  finishes the execution of one command, it seeks
  the next control statement from the users
  keyboard.
• i.e., the shell
• Goal is to give the illusion that each user has
  own machines.
• Response time is a priority.

18
Computer Hardware Review
Monitor
Bus

• Components of a simple personal computer

19

• Special registers
• Program counter.
• Stack pointer.
• Process Status Word (PSW).

20
Computer Hardware Review

• (a) A three-stage pipeline
• (b) A superscalar CPU

21

• CPU has two modes user and kernel.
• Application obtains OS services through a system
  call.
• Traps to operating system and switches to kernel
  mode.

22

• Typical memory hierarchy
• numbers shown are rough approximations

23

• Structure of a disk drive

24

• One base-limit pair and two base-limit pairs

25
I/O Devices

• Manufacturer provides device driver (talks to the
  device).
• OS talks to device driver.
• Three ways to handle I/O operations
• Busy waiting.
• Interrupt driven
• Direct Memory Access (DMA)

26
(a)
(b)

• (a) Steps in starting an I/O device and getting
  interrupt
• (b) How the CPU is interrupted

27

• Structure of a large Pentium system

28
Operating System Concepts

• A process tree
• A created two child processes, B and C
• B created three child processes, D, E, and F

29
Operating System Concepts

• (a) A potential deadlock. (b) an actual deadlock.

30
Operating System Concepts

• File system for a university department

31
Operating System Concepts

• Before mounting,
• files on floppy are inaccessible
• After mounting floppy on b,
• files on floppy are part of file hierarchy

32
Operating System Concepts

• Two processes connected by a pipe

33
Steps in Making a System Call

• There are 11 steps in making the system call
• read (fd, buffer, nbytes)

34
Some System Calls For Process Management
35
Some System Calls For File Management