System Software

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System Software
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Components of System Software

• System Software enables application software to
  interact with the computer and manages the
  computers resources
• Operating System (OS) The principal component of
  system software, manages basic operations of the
  computer
• Device Driver Helps the computer control
  peripheral devices
• Utility Program Supports, enhances, and expands
  capabilities of existing programs
• Language Translator Translates high-level
  language programs to machine code

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Utility Programs

• Backup Makes a duplicate copy of the specified
  data
• Data-Recovery Restores data that has been
  physically damaged or corrupted
• Virus Protection Scans files, detects, and
  removes viruses
• Data Compression Removes redundant elements,
  gaps, and unnecessary data from files
• Disk Scanner Cleanup Detects and removes
  unnecessary files, detects and corrects disk
  problems
• Defragmenter Finds all scattered files on a hard
  disk and reorganizes them as contiguous files

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Fragmentation Visualized
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The Operating System

• The operating system (OS) is the principal
  component of system software
• It consists of the master system of programs that
  manage the basic operations of the computer
• Some of the functions of the OS are
• Memory management
• CPU scheduling
• Process management
• File management
• Security management

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Common Operating Systems

• Software Platform A particular operating system
  on which a computer is based
• GUI vs. command driven operating systems
• Disk Operating System (DOS) The original OS by
  Microsoft, command-driven user interface
• Windows 3.X, 95, 98, etc.
• Mac OS For Apple Macintosh computers, first
  GUI-based OS
• Network Operating Systems Netware, Linux, Unix,
  etc.
• What factors would you consider when selecting a
  new OS?

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The Booting Process

• Booting is the process of loading the OS into the
  computers main memory
• When the computer is turned on, diagnostic tests
  are performed to check that the CPU and other
  parts of the system are running properly
• The CPU automatically begins executing the BIOS
  stored in the ROM
• The OS is loaded from the hard disk to the main
  memory (RAM)
• Control is passed to the OS
• Cold vs. Warm Boot
• The Boot Disk A CD that contains all the files
  needed to launch the OS
• When the computer is turned on with the boot disk
  in the disc drive, the OS files are forced to the
  BIOS, i.e. it takes precedence over obtaining the
  OS files from the hard drive
• Once in the OS is loaded, one can perform
  maintenance, troubleshooting, etc.

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Process

• A process is a program in execution. Program is a
  static set of instructions. Process is a dynamic
  entity that represents the program while it is
  being executed.
• The process states
• New
• Ready
• Running
• Waiting
• Terminated

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Process Management

• Process Management is the act of carefully
  tracking the progress of a process and all of its
  intermediate states.
• CPU Scheduling is determining which process in
  memory is executed by the CPU at any given point.
  
• Mainly CPU scheduling is done in 2 ways
• Batch processing
• Time sharing

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Batch Processing

• The first Operating System was Human Operator.
• Operator used to organize various jobs from
  multiple users into batches of jobs that needed
  the same resources . Together program and set of
  instructions in together are called Job.
• Modern OS incorporate batch processing by
  allowing the user to define a set of OS Commands
  as a batch file .bat to control the processing of
  large program.

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Timesharing

• A timesharing system allows multiple users to
  interact with a computer at the same time. They
  all timeshare the same resource.
• Timesharing create an illusion that each user has
  exclusive access to the computer. So they do not
  have to compete for resources.
• Though is what exactly happens behind the scene.
• The OS Manages the sharing of the resources,
  including CPU behind the scene.
• Each user has his/her own Virtual Machine, in
  which all system resources are (in effect)
  available for use.

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CPU Scheduling

• CPU Scheduling is the act of determining which
  process in the ready state should be moved to the
  running state.
• This happen when a process switches from running
  state to waiting state or terminated state.
• Scheduling offers under 2 circumstances
• Non-preemptive Scheduling Scheduling that occurs
  when the currently executing process gives up the
  CPU voluntarily.
• Preemptive Scheduling Scheduling that occurs
  when the OS decides to favor another process,
  preempting the currently executing process
• Turnaround Time The scheduling metric that
  measures the elapsed time between a process
  arrival in the ready state and its completion

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Approach to CPU Scheduling

• First-come first-serve (FCFS) diagram 1. Avg
  turnaround time 529.
• Shortest job next (SJN)- diagram 2. Avg
  turnaround time 435.
• Round robin- Every process is treated the same.
  Eventually all preempted process will be given
  another time slice on the CPU.
• Time slice - The amount of time each process
  receives before being preempted and returned to
  the ready state to allow another process its
  turn. Avg turnaround time 668

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Memory Management

• The OS must employ techniques
• Track where and how a program resides in memory
• Convert logical program addresses
• A logical address is a value that specifies a
  generic location relative to the program but not
  with respect to the actual main memory device
• A physical address is an actual address in the
  main memory device
• Address binding The mapping from a logical
  address to a physical address
• Three memory management techniques
• Single contiguous memory management
• Partition memory management
• Paged memory management

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Single Contiguous Memory Management

• The approach to memory management in which a
  program is loaded into one continuous area of
  memory

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Partition Memory Management

• Fixed Partition Technique The memory is divided
  into a specific number of partitions into which
  programs are loaded
• Dynamic Partition Technique The memory is
  divided into partitions as needed to accommodate
  programs
• Partition selection
• First fit
• Best fit
• Worst fit
• Which partition selection technique is better?

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Paged Memory Technique

• An approach in which process are divided into
  fixed-size pages and stored in memory frames when
  loaded
• Frame A fixed-size portion of main memory that
  holds a process page
• Page A fixed-size portion of a process that is
  stored in a memory frame
• Page-Map Table (PMT) The table used to keep
  track of page/frame relationships

Memory
P1 PMT