Operating System Structures

1
Operating System Structures
Chapter 3
2
Operating System Structures

• OS Design Constraints
• OS Basic Functions
• OS Structures

3
Design Constraints

• Performance
• Protection Security
• Correctness
• Maintainability
• Commercial factors

4
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 gt should not use
  too much of machine resources
• Provide an environment in which programmers can
  produce solutions in a cost-effective manner
• gt trade off

5
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 gt
  trusted vs un-trusted software
• Maintainability - refers to the ease with which
  software can be changed/extended, bugs can be
  fixed, etc.

6
OS Basic Functions

• Device management
• Process resource management
• Memory Management
• File Management

7
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

8
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

9
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

10
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 s1112

11
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

12
Basic OS Functions
13
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).

14
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.