Operating Systems
Introduction I
Aslam Safla
aslam@cs.uct.ac.za
OS Module Overview
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Introduction and OS Structures (Chapters 1-2).
Processes and Threads (Chapters 3-4).
Process Synchronization, Scheduling, Deadlocks (Chapters 5-8)
Main and Virtual Memory (Chapters 9-10).
File-Systems and I/O (Chapters 11-15).
Protection (Chapter 17).
OS Module Textbook
Operating System Concepts – 10th Edition (2018):
Avi Silberschatz
Peter Baer Galvin
Greg Gagne
John Wiley & Sons, Inc.
ISBN 978-1-118-06333-0
https://codex.cs.yale.edu/avi/os-book/OS10/index.html
OS1 Practical Assignment
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Assignment: (Closed Practical):
Memory management – Paging algorithms.
60-minute slots: 21th / 22nd of April.
Approx. 7.5% of course mark.
Check Amathuba for updates and sign-up
procedure!
Why Study Operating Systems (OS)?
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OS are fundamental to CS:
Most people use a handful of mature OS.
Hard to get people to switch OS.
Hard to have impact with a new OS.
Resource consumption is an OS issue:
Battery life, radio spectrum, …
Security is an OS issue.
New “smart” devices need new OS.
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What is an
Operating System?
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Is an
Operating System (OS)
just a program?
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OS = Program!
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UNIX OS (1972): Rewritten in C to move UNIX kernel code from
assembly to high level language (do same tasks with less code).
Microsoft Windows:
MS Windows kernel developed mostly in C (some in assembly).
Mac OS:
OS X kernel is written mostly in C.
Mobile
iOS, Android and Windows Phone kernels: Coded in C (just mobile
adaptations of existing Mac OS, Linux and Windows kernels).
Custom Operating Systems
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Nintendo Switch system software, aka: Horizon (2017):
Written in C, C++, proprietary microkernel architecture.
Closed source.
OS = The First Program
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A program that lets you run other programs.
A program providing controlled access to resources:
CPU.
Memory.
Devices: Display, keyboard, mouse.
Persistent storage.
Network.
System Software
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General piece of software with common functionalities
that support many applications.
Examples:
C compiler and library functions.
Database management system.
OS: Software that operates directly with system
hardware.
An OS is like these things…
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OS = Illusionist Government !?
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OS as an illusionist:
Clever resource management to overcome hardware
limitations.
OS as a government:
Protects users from one another.
Allocates resources efficiently and fairly.
Provides an environment within which other programs
can do useful things.
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OS: System View
OS is a resource allocator:
Manages all resources.
Handles conflicting requests for efficient & fair
resource use.
OS is a control program:
Controls execution of programs – prevent errors –
ensures programs run.
An OS is an Abstraction
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Interface: Between users and computer (hardware).
Convenience: Hides tedious stuff.
Efficiency and Control: Allocates resources, allows
parallel applications, protects information.
Reality versus Abstraction
Reality
Abstraction
A single CPU
Multiple CPUs
Limited RAM capacity
Infinite capacity
Mechanical/SSD disk
Memory speed access
Insecure and
unreliable networks
Many physical
machines
Reliable and secure
A single machine
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Why have
Abstractions?
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Why have Abstractions?
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Reduce functional complexity.
Provide single abstraction over multiple devices.
Resource sharing:
Efficiency.
Fairness.
Security.
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Example I: User Abstractions
End User
View
Application
Developer View
System
Developer View
Example II: Disk Abstractions
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Direct
control
write()
abstraction
fprintf()
abstraction
Example III: Process Abstraction
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OS Abstractions
Hardware
Disks
Memory
Processors
Network
Monitor
Keyboard
Mouse
Operating System:
Files
Programs
Threads of control
Communication
Windows, graphics
Input.
Files as an Abstraction of Memory
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Issues with Files
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Naming.
Allocating space on disk (permanent storage)
How to organise for fast access and minimise waste.
How to shuffle data between disk and memory
(high-speed temporary storage).
How to handle crashes and (disk / memory) errors.
Programs
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Memory Sharing
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Virtual Memory
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Resource Sharing
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OS = Kind of Virtual Machine!
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Hides complexity and limitations of hardware from
application developers.
Applications
Operating system
(virtual machine)
Physical machine
Virtual machine interface
Physical machine interface
Application Virtual Machines
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Examples?
Application Virtual Machines
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VMware:
Hypervisors
Java Virtual
Machine (JVM)
Example: Java Virtual Machine
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Concurrency
vs
Parallelism?
Concurrency
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Parallelism
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Concurrency vs. Parallelism
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Concurrency: Can exist on single CPU: Multi-tasking OS.
Parallelism: Speed-up via N computations in parallel.
Problems get tricky when you introduce parallelism:
Multi-core.
Multiple CPUs.
e.g.: C/C++ with MPI parallel processing libraries.
Current popular idea of common shared state between
multiple threads is risky.
Concurrency and Parallelism
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Historical growth in
single-processor
performance and a
forecast of processor
performance to 2020
What do these have in Common?
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Von Neumann Computer Architecture
+ Operating System
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Von Neumann architecture
Main Memory
central
processing
unit
data
+
machine
instructions
Operating
System
abstraction
compilation
global data
+
sequence of
commands
Problems..?
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Currently ~ 5–15% of the world’s energy is spent in some
form of data manipulation, transmission, or processing.
> 5 billion transistors per chip common-place.
Transistor sizes now approaching 10 nm.
Parallel computing (Multi-core / CPU) now common-place.
Increased overall energy consumption.
Current predictions: “Data processing centres will end up
costing more energy than we have”1
1. https://theconversation.com/data-centres-are-guzzling-up-too-much-electricity-can-we-make-them-more-efficient-235591
New Types of OS?
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Can we design hardware and software with a
completely different model of computation ?
Neuro-Morphic Computing
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System architecture emulates brain (neural) structure.
Inherently parallel processing.
Ideal for “biological” machine learning algorithms – e.g.:
speech / facial recognition.
What would a neuro-morphic OS look like?
Quantum Computing
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Theorised to be exponentially faster than classical computers:
Solving classical hard CS problems (e.g. factorizing integers).
Information stored as quantum bits (qubits).
30 qubits ~ 10 tera-FLOP (1012) computer.
IBM,16 qubit processor1.
What would a Quantum computing OS look like?
1. https://www.sciencenews.org/article/quantum-computers-are-about-get-real
New Types of OS?
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What would Operating Systems for these
computer architectures look like ?
Reading
Operating System Concepts – 10th Edition (2018):
Chapter 1: Introduction
https://codex.cs.yale.edu/avi/osbook/OS10/index.html
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