Post on 18-Apr-2020
Operating Systems
Operating Systems - Winter 2012
Andrew S. TanenbaumMelanie Rieback
Arno Bakker
Design and Implementation
Vrije Universiteit Amsterdam
Outline
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• Introduction• What is an OS?
• Concepts
• Processes and Threads
• Memory Management
• File Systems
Operating Systems 2012
Chap 1 - Overview
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• What is an Operating System?
• Concepts
• System Calls
• Structure
Operating Systems 2012
What is an OS?
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Operating Systems 2012
2 Views on OSes
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• OS as a Virtual Machine
• Extending the HW functionality
• Hides the messy details of programming the HW
• OS as a Resource Manager
• Protects against simultaneous usage of resources
• Fair sharing of resources (scheduling)
• Resource accounting
Operating Systems 2012
How to View an OSOperating Systems 2011
Vrije Universiteit Amsterdam Slide 16
OS
Program
System calls
Concept: ProcessesOperating Systems 2011
Vrije Universiteit Amsterdam Slide 17
Multiple ProcessesOperating Systems 2011
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some_program
init
shell
System CallsOperating Systems 2011
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Hardware
Operating SystemSystem Calls
LibrariesLibrary functions
Applications / Processes
Instruction Set Architecture
• System Calls are the interface the Operating System offers to applications.• Problem: Mechanics of issuing a system call are highly machine dependent• Solution: Provide a library to allow system calls from C programs: libc
Bashlibc
Linux kernel
x86_64
System Calls: Process Management (1/2)
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System Calls: Process Management (2/2)
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System Calls: SignalsOperating Systems 2011
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Concept: Mounting (1/2) Operating Systems 2011
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File System Mounting (2/2) Operating Systems 2011
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Special Files (1/2) Operating Systems 2011
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Storage devices are mapped into the file tree via mounting. Idea: do this for all devices.
Mechanism: Special files in /dev
Two types:
Special Files (2/2) Operating Systems 2011
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System Calls: FilesOperating Systems 2011
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System Calls: DirectoriesOperating Systems 2011
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System Calls: Implementation Operating Systems 2011
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OS Structure: UNIXOperating Systems 2011
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OS Structure: LinuxOperating Systems 2011
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Operating Systems
Operating Systems - Winter 2012
Chapter 2 - Processes
Vrije Universiteit Amsterdam
Chap 2 - OverviewOperating Systems 2012
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• Scheduling Processes
• Threads
Recall: Process
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Operating Systems 2012
One CPU, Many Processes
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Operating Systems 2012
• Processes share the CPU(s)• A scheduler determines which process to run next• Keeps track of the process state• Following some scheduling policy (random robin, shortest
job first, etc).
Process States
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Operating Systems 2012
Context SwitchingOperating Systems 2011
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Process ImplementationOperating Systems 2011
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ProcessTable: ps -ef
ThreadsOperating Systems 2011
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Threads: Minimal SupportOperating Systems 2011
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Threads – Some ProblemsOperating Systems 2011
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Mutual ExclusionOperating Systems 2011
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Operating Systems
Operating Systems - Winter 2012
Chapter 4 – Memory Management
Vrije Universiteit Amsterdam
Chap 4 - OverviewOperating Systems 2012
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• Memory Management
• Paged Memory
• Virtual Memory
• Segmentation
Memory Management – SimpleOperating Systems 2012
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Memory Management - ComplexOperating Systems 2012
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Multiple processes in the same memory
Paged Memory Systems (1/2) Operating Systems 2012
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Paged Memory Systems (2/2)
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Virtual Memory Operating Systems 2012
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• Idea: Not all virtual pages have to be in physical memory• Instead stored on disk -> cheap storage• In swap partition• Much more memory available• Works if not all pages are used at the same time
Segmentation Operating Systems 2012
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Stack
Data
Code
N
0Code Data Stack
N
0
• Segments can grow independently• Hardware helps to map segments to virtual memory• Hardware helps to protect: read-only, no-execute
Operating Systems
Operating Systems - Winter 2012
Chapter 5 – File Systems
Vrije Universiteit Amsterdam
Chap 5 - OverviewOperating Systems 2012
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• Files
• Directories
• File system implementation
• UNIX/MINIX filesystem
Directories
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Operating Systems 2012
i-node
File Attributes
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Operating Systems 2012
Directories – Pathnames
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Operating Systems 2012
File System Design
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Operating Systems 2012
File Storage: Disk Layout
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Operating Systems 2012
File Storage – Inodes
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Operating Systems 2012
File Storage – UNIX
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Operating Systems 2012
File Storage – Name Resolution
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Operating Systems 2012
Disk Space Management (1/2)
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Operating Systems 2012
File System Consistency
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Operating Systems 2012
Buffer Cache
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Operating Systems 2012
Log-Structured File Systems
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Operating Systems 2012
MINIX Filesystem
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Operating Systems 2012
MINIX Superblock
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Operating Systems 2012