Download Chapter 3: Operating System Structures

Operating System Structures
Chapter 3
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Operating System Structures
• OS Design Constraints
• OS Basic Functions
• OS Structures
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Design Constraints
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Performance
Protection & Security
Correctness
Maintainability
Commercial factors
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Performance
• People use computers for the potential of rapid
information processing
• There are several measures of performance
– throughput
– response time
• The OS is an overhead function => should not use
too much of machine resources
• Provide an environment in which programmers
can produce solutions in a cost-effective manner
==> trade off
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Correctness & Maintainability
• Correctness - refers to whether OS functions meet
their requirements.
• Correctness is the most basic requirement on
which all other requirement are based- e.g.
security depends on correct operation of OS =>
trusted vs un-trusted software
• Maintainability - refers to the ease with which
software can be changed/extended, bugs can be
fixed, etc.
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OS Basic Functions
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Device management
Process & resource management
Memory Management
File Management
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Device Management
• OS Manages the allocation, sharing and isolation
of I/O devices (disks, tapes, terminals, etc.)
• Most Operating Systems treat all devices in the
same general manner
– UNIX treats them all like files
• Chapters 4 & 5 discuss Device Management
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Process & Resource Management
• A process is the basic unit of computation
• Resources are the elements needed by a process so
that it can execute
– CPU, Memory, I/O devices, data etc.
• OS provides a set of process management
mechanisms: for process creation , blocking,
resumption, termination ,etc
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Process & Resource Management
• OS manages computer resources so that multiple
processes can execute simultaneously
– CPU scheduling
– resource allocation, sharing & process
synchronization
– resource allocation
• Chapters 6 - 10
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Memory Management
• Allocation and use of the primary memory
resource
– memory allocation among competing processes
– enforce memory isolation and sharing
• Most modern OS support virtual memory.
– Virtual memory allows processes to access
data in secondary storage as if it were in main
memory.
• Chapter s11&12
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File Management
• Information that need to be saved "permanently"
must be stored in a secondary storage device e.g. a
disk, tape, etc.
• Files are an abstraction of secondary storage devices
• File manager is responsible for
– managing the file system: file & directory
creation and manipulation
– mapping files into physical storage devices
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Basic OS Functions
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OS Structures-Simple Approach
• MS-DOS - written to provide the most
functionality in the least space
– not divided into modules
– Although MS-DOS has some structures, its
interfaces and levels of functionality are not
well separated.
• application programs are able to access BIOS
routines directly (bypassing DOS).
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OS Structures--UNIX
• UNIX -- modular
• UNIX consists of two separate parts:
– System programs (Shells and commands,
compilers and interpreters, system libraries)
– The kernel: part of OS that is most critical to
its correct operation (trusted)
• provides CPU scheduling, memory management,
file management, and other operating system
functions.
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