Introduction
Operating Systems’ Concepts and Structure
Lecture 1
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TUCN. Operating Systems. Lecture 1
Contents
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Definition of an Operating System (OS)
Role of an Operating System
History of Operating Systems
Classification of Operating Systems
Specific terms and concepts
Structure of an OS
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The Definition of an OS
Where comes the OS in?
A computer system consists of:
User software
System software
Hardware
User
Applications
Compilers
Editors
Shells
Operating System
System hardware
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The Definition of an OS
What is an OS?
• A system software
• A collection of procedures that:
– manage all the system’s hardware resources
– provide the users the environment in which
they can:
• use the system resources
• run their own applications
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The Role of an OS
• Extended or virtual machine
• The external or the user point of view
• A top-down perspective
– Hides the complexity of using the hardware devices
– Provides the user a more convenient view of the system resources
– Purpose: Convenience
• Resource manager
• The inside or the designer point of view
• A bottom-up perspective
– Brings the hardware resources in a functional state
– Provides each program with time and space for using resources
– Purpose: Efficiency
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A Classification of OSs
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Mainframe operating systems: OS/390
Server operating systems: UNIX, Windows 2000, Linux
Multiprocessor operating systems
PC operating systems:
• Windows 98, Windows ME, Macintosh, Linux
• Real-time operating systems: VxWorks, QNX
• Embedded operating systems:
• PalmOS, Windows CE, Windows Mobile, Symbia
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Specific Terms and Concepts
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Batch systems: no user interaction
Multiprogramming: multiple programs loaded in memory
Time-sharing: each process receives slices of CPU time
Interactive systems: provides quick response to user’s actions
Multi-user: distinction between users
Network OS: users aware of the existence of multiple computers
Distributed OS: looks like a traditional single-processor system
Processes, Files, System Calls
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Computer Hardware (1)
• An OS is closely tied to the HW it runs on
• HW components
– CPU
– Memory
– I/O devices
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Monitor
Keyboard
Storage devices (HDD, Floppy etc.)
Others
– BUSes
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Computer Hardware (2)
Monitor
BUS
Tanenbaum, Fig. 1-5.
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CPU
• Functionality
– fetch instructions from memory, decode and execute them
• Instruction set
– has a specific set of instructions that can be executed
– specific executable programs each processor can run
• Registers
• Program counter
• Stack pointer
• Many others – architecture dependent
• Machine state – saved at context switch
• Kernel vs. User mode of execution
– switches between
• system calls
• hardware exceptions, interruptions
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Memory
• Should be extremely fast, large and cheap
• Hierarchy of layers
– Registers: fastest, no delay, but limited size
– Cache memory
• cache hits and misses
– Main memory – RAM (Random Access Memory)
– HDDs
• 2 orders of magnitude cheaper and larger then RAM, but 3 orders of
magnitude slower
• mechanical device – heads, tracks (cylinders), sectors,
– Magnetic tapes
• used as a backup for very large data sets
• very slow, but very cheap and removable
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I/O Devices
• Components
– controller and the device itself
• Controller
– Directly controls the physical device
– Receives commands from the OS
• Device driver
– Supplied by controller manufacturer
– Inserted into the OS – run in kernel mode
• Functionality
– Busy waiting
– Interrupts
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Processes
• Definition
• A program in execution
• Consists of: executable code, data, stack, CPU registers
value, and other information
• A process hierarchy (tree)
• A created two child processes:
B and C
• B created three child processes:
D, E, and F
• Process synchronization
• Inter-Process Communication (IPC)
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Files
• Definition
• A collection of related information
• An abstraction of data stored on HDD
• A process tree
• File system mounting
• File linking
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System calls (1)
• Definition
– a call to an OS service
– a trap into the OS code
• Examples of system calls
– File manipulation: open(), read(), write(), lseek(), close() …
– File system management: mkdir(), mount(), link(), chown() …
– Process management: fork(), exec(), wait(), exit() …
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System Calls (2)
Steps in making a system call
There are 11 steps executing
the system call:
read (fd, buffer, nbytes)
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The Structure of an OS
Architectures(1). Monolithic OS
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The Structure of an OS
Architectures (2). Layered OS
The Structure of the THE operating system
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The Structure of an OS
Architectures (3). Client-Server
The client-server model
A distributed OS
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The Structure of an OS
Architectures (4).Advantages …
• Advantages of micro-kernels
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the modules run in user mode  protection against bugs
adaptability to use in distributed systems
forces the programmers to adopt a modularize approach
easily ported to other architectures
better use of RAM than monolithic ones
• Modules in monolithic systems (Linux) - advantages
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monolithic OS faster than micro-kernel OS
modularized approach
platform independence
frugal main memory usage
no performance penalty
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The Structure of an OS
Components
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Process manager: creates, schedules and destroy processes
Memory manager: allocates and releases memory
Disk manager
I/O devices manager
File system: create, read, modify, remove etc. files
Communication system
Protection system
Shells
• text interface – command interpreter
• graphical interface
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Readings
• Andrew Tannenbaum, “Modern Operating
Systems”, second edition, Prentice Hall,
2001, pgs. 1-20, 34-63
• D. Bovet, M. Cesati, “Understanding
Linux Kernel”, O’Reilly, 2001, pgs.11-12
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