Lecture 1: Introduction to operating systems

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Exam

Introduction to operating systems and their history

Important questions:

• Why were operating systems developed initially?
• How did the features of operating systems evolve along with the development of the available hardware?
• How do we define the term "operating system" today?

You do not need to know details about the historical computers and operating systems discussed in that lecture

Defining an OS

• There are many definitions of the term 'operating system'
• Common ideas are:
  • The OS serves the users and their programs, it is never an end to itself
  • The OS has to know the hardware in detail and provides suitable abstractions to application programs
• Hardware and application requirements determine the services provided by an OS
  • From this, its structure and functionality derives
• To understand which hardware abstractions are provided by operating systems today, we take a look at their history of development along with advances in hardware and typical applications

In the beginning: Punched cards

• Punched cards - paper cards with holes indicating a '1'
• Since 1725 used to control weaving looms
• Used by Hermann Hollerith for the 1890 US census
  • Hollerith and two other companies formed IBM later
• Used until 1970s as versatile memory

The first Norwegian computer

• NUSSE - 'Norsk Universell Siffermaskin Selvstyrt Elektronisk", developed at UiO
• Constructed between 1950-1955
• 1000 vacuum tubes, 2 kB main memory, 40 kHz clock time

The first computer at NTNU (NTH)

• GIER - 'Geodætisk Instituts Elektroniske Regnemaskine', from Denmark in 1962
• 5 kB main memory
• Already provided:
  • Operating system
  • Algol-60 compiler
  • Runtime library with virtual memory management

Serial processing

• Non-interactive programming of computers
  • Input via punched card reader
  • Output via printer
  • Errors indicated using lamps
• Minimal CPU utilisation
  • Because of slow I/O devices
• First system software as reusable program libraries
  • Linker, loader, debugger, device drivers

Simple batch systems (from 1955)

• Reduced frequency op operator interactions
• First operating systems: 'resident monitors'
  • Interpretation of job control commands
  • Loading and execution of programs
  • Device control
• The monitor stayed resident in memory and executed one application after the other
• Problems due to erroneous applications:
  • Program doesn't terminate
  • Writes in the memory of the resident monitor
  • Accesses card reader directly and interprets control commands as data
• Solutions:
  • Addition of a timer circuit generating interrupts
  • Traps for erroneous programs
    • Fence register to realise primitive memory protection
    • Privileged operating mode of the CPU (supervisor mode)
      • Deactivates fence register
      • Allows input and output

Input/Output bottleneck

• Problem: CPU is faster than card reader and printer
  • Valuable compute time is wasted by (active) waiting
• Solution 1: off line processing
  • Enabled by magnetic tape dries
  • Parallelisation of I/O using multiple satellite computers
• Solution 2: spooling
  • Enabled by magnetic disk drives (random access) and direct memory access (DMA)
  • Computation and I/O can now overlap
  • Requires rules for processor allocation

Multiprogramming (from 1965)

• Despite spooling, a single program does not utlise the CPU efficiently
  • System operation alternates between CPU bursts and I/O bursts, during with the CPU has to wait
• With multiprogramming, the CPU works on multiple jobs at the same time
• Consequence:
  • The operating system becomes increasingly more complex
    • Handling concurrent I/O activites
    • Managing the main memory for multiple programs
    • Internal management of pragrams in execution (processes)
    • Processor scheduling
    • Multi user operation: security and accounting
• Memory managmement
  • Programs to be started need an assigned memory range
• Memory protection
  • Simple fence register is no longer sufficient to isolate processes from each other
  • Solution: use a simple memory management unit (MMU)
• Process management
  • Every 'program in execution' has its own context
  • When switching between processes, the context has to be switched as well

Dialog computing (from 1970)

• New I/O devices enable interactive software
  • Keyboard, screen, later mouse
• Time sharing operation
  • Enables acceptable response times for interactive users
  • Timer interrupts ensure the preemption of processes which run (too) long
• System programs enable interactive software development
  • Editor, shell, compiler, debugger
• Disks and file systems allow to allow access to programs and data at any time