Computers

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Computers

• Operating System Essentials

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Operating Systems
PROGRAM
HARDWARE
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Operating Components
APPLICATION PROGRAMS
MEMORY
SYSTEM PROGRAMS (COMPILERS, etc.)
OPERATING SYSTEM
KERNEL
MACHINE LANGUAGE
MICROPROGRAMMING
ROM
PHYSICAL EXECUTION
CPU
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System Structure Layers

• Processor Hardware functions circuits,
  instruction set, procedures, interrupts
• Process management multiprogramming, management
  of secondary storage, logical addressing
• External resource management communication among
  process, file management, device access and
  addressing, user support

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OS Functions

• User Interface
• Resource Management
• Evolution

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User Interface Functions

• Create programs
• Execute programs
• Access I/O devices
• Manage file access
• Provide shared access
• Manage error detection
• Provide accounting

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Resource Management

• Shares resources among applications
• Increases efficiency

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Evolution

• Support hardware upgrades
• Enables operating system upgrades and additional
  features
• Fixes

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Essential OS Functions

• Process management
• Memory management
• Information protection and security
• Scheduling and resource management
• System architecture

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Process

• Consists of
• Executable program
• Data and data resources
• Execution context register contents, priorities
  and module status

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Process Management

• Multiprogramming
• Running several programs at a time to increase
  cpu utilization
• Time sharing
• Allowing multiple interactive users to log in at
  the same time
• Real time transaction processing
• Allow multiple users/programs to use the same
  copy of a program at once

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Batch Multiprogramming (Short term dispatching)
READY
READY
READY
NEW
RUNNING
HALTED
NEW
RUNNING
ERROR/ COMPLETE
WAITING
WAITING
I/O
I/O
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Process Control Block (Short term scheduling)
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Dispatching lower level process scheduling

• 50 - 60 automatic interrupts per second
• Returns control to the OS for rescheduling
• preemptive scheduling
• run to completion

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Process Management Problems

• Synchronization correct management of
  interrupted processes
• Mutual exclusion keeping shared resource use
  separate
• Determinate program operation programs get the
  same result every time independent of what else
  is running
• Deadlock

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Memory Management

• Virtual memory and file management
• Isolation
• Automatic allocation and management
• Support modular programming
• Protection and access control
• Long-term storage

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Addresses

• Physical address actual memory location.
  NEEDED BY THE CPU
• Relative address offset from a reference
  physical address. NEEDED BY THE OPERATING SYSTEM
• Logical address address within a programmed
  unit (e.g. page). NEEDED BY APPLICATION PROGRAMS

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Virtual Memory
FRAME NUMBER OFFSET
PAGE NUMBER OFFSET
PAGE TABLE
PAGE TABLE
PAGE TABLE
Page Frames
Pages
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Page Table Access

• A page table is an index to the current location
  of a page. Access can be
• Swapped
• Page Segmentation (hierarchical)
• Hashed

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Translation Lookaside Buffer Page Cache
ALU
CNTL
.....
CACHE
BUS
MAIN MEMORY
DASD
TLB
Page Frames
Pages
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Information Protection and Security

• Access control authorization and access
  limitation
• Information flow control manage the
  distribution of information to the proper
  location
• Certification assure that protection and
  security systems are working correctly

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Scheduling and Resource Management

• Considers
• Fairness
• Differential response
• Efficiency

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Modern Operating Systems

• Microkernel Architecture
• Multithreading
• Symmetric pultiprocessing

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Virtual Machine O/S

• Users think they have the entire machine
• Copies of machine can execute the complete
  machine language
• May run different operating systems in different
  partitions

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OS Management