Software Hierarchy

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Software Hierarchy
Software
Development software
System software
Application software

• compilers
• interpreters
• editors
• debuggers
• Integrated
• Development
• Environments
• (IDE)

• word processing
• presentation
• spreadsheet
• database
• desktop publishing
• multimedia
• communication
• graphics

Utility Programs
Device Drivers
Operating system
Shell
Kernel
Allow input/output devices to communicate with
programs and other system components
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The Components of System Software

• Operating system - the principal component of
  system software
• Device drivers - help the computer control
  peripheral devices
• Utility programs - support, enhance, or expand
  existing programs

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Structure of the OS

• The operating system shell includes the user
  interface (UI).
• Users only interact with the OS through the UI.
• The UI can be
• Command/character-based (e.g., DOS or UNIX)
• Graphical user interface (GUI), involving
  windows, menus, icons, etc.

kernel
kernel - program which remains in main memory
while the computer is running, and directs other
nonresident programs to perform tasks that
support application programs
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What Is an Operating System?

• The operating system
• A collection of programs that help you use the
  computer.
• Acts as a smart assistant that moves controls the
  flow of information to various components and
  other programs.
• Manages the usage, storage, and access of
  programs, data, and processes.

Common Tasks Performed by the OS
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Where is the OS Stored?

• Where does the operating system reside?
• ROM (Read Only Memory)
• ROM is non-volatile memory that contains the
  skeleton operating system, along with information
  about where the OS is stored on the Hard disk or
  other external storage.
• The skeleton operating system allows use of
  keyboard and both floppy and hard disk drives.
• RAM (Random Access Memory)
• The main part of the operating system is
  transferred from a secondary storage (e.g., hard
  disk) to RAM when the computer is first
  turned-on.
• This is called the booting process or
  boot-up.
• After the boot-up, a portion of RAM is taken up
  by the OS and other system software, while other
  portions are available for loading application
  software or data.

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The Booting Process
(BIOS)
BIOS stands for basic input/output system basic
input/output system
(RAM)
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The Booting Process
(BIOS)
(RAM)
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Overview of The Booting Process
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Main Operating System Functions

• Task management
• preparing, scheduling, and monitoring of tasks
  for continuous processing by the CPU
• Memory management
• allocation of memory for various tasks transfer
  of data and programs from external storage to
  memory and back virtual memory management cache
  management
• Device management
• controlling flow of data to an from input/output
  devices, and management of device drivers
• File and data management
• controlling how files are created, accessed,
  organized, copied, and modified controlling and
  managing the storage of data in external storage
  devices
• System monitoring
• monitoring of system resources and devices error
  detection and recovery

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Some Terminology

• Process
• A process is an instance of a program running in
  a computer. In Unix and some other operating
  systems, a process is started when a program is
  initiated. A process is a running program with
  which a particular set of data is associated so
  that the process can be kept track of.
• Task
• A task is a basic unit of processing that an
  operating system controls. A process may be a
  single task or may involve multiple tasks that
  are performed together or consecutively.

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Task Management Concepts

• Multi-tasking
• Running more than one task (or process)
  simultaneously.
• Each process stealing or sharing CPU time.
• Such as playing a game while a large document is
  being printed.
• Each process is allocated a CPU time slice at
  the end of the time slice the process in
  interrupted and its state is saved until the
  CPU can come back to the process CPU is then
  allocated to the next process on the queue.
• Context Switching
• Switching from one process or one user to
  another.
• Such as from a word processor to a spreadsheet
  and back again (both reside in RAM).

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Multi-tasking
CPU Time shared between process A and process B
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Task Management Concepts

• The Process States

The process life cycle
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Task Management Concepts

• CPU Scheduling Determining which process in the
  ready state should be moved to the running state
• That is, decide which process should be given
  over to the CPU
• The operating system must manage a large amount
  of data for each active process
• Usually that data is stored in a data structure
  called a process control block (PCB)
• Each time a new process is moved to the running
  state
• The CPU must store the intermediate data for the
  currently running process into its PCB.
• Then, the CPU most load the running state of the
  new process from its PCB (this is loaded into
  special memory devices inside the CPU called
  registers).
• This exchange of information is what we call a
  context switch

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Task Management Concepts

• Multi-Programming
• Same as multi-tasking, but there are multiple
  users that are running programs (e.g., multiple
  users logged in on the same computer). OS needs
  to be able to switch context and allocate CPU and
  memory resources among multiple users.
• Parallel processing (Multiprocessing)
• Computing that is done with more than one CPU.
• Several processors or CPUs are simultaneously
  computing a program.
• Load Balancing OS tries to manage the allocation
  of tasks to multiple CPUs, in order to optimize
  the load on each processor.
• Scaling OS needs to be able to break up tasks
  into independent units that can be processed
  simultaneously by different processors.
• Distributed processing
• Makes use of a network.
• Decentralizes and distributes the computing needs
  over several interconnected computers.
• Requires a network operating system that can
  handle allocation and management of tasks across
  the network among multiple computers.

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Task Management Summary
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Memory Management Concepts

• At any point in time memory is divided into a set
  of partitions, some empty and some allocated to
  running processes.
• A portion of the memory is always reserved for
  the operating system and other system processes.
• When a process is activated, its memory address
  (location of the first instruction in the
  program) and the total space (length) for the
  process are stored the CPU registers.
• This way, the CPU will know how to get back to
  the process as it switches among different
  running processes.

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Memory Management Concepts

• Cache memory
• If the primary memory were as large as ever
  needed, the following ideas would not be
  necessary.
• Cache memory Addresses the concerns of speed and
  efficiency (two types).
• 1. Disk cache - saves the most frequently used
  parts of the program being run or executed in the
  RAM memory - it will be there ready to go (very
  fast).
• 2. RAM disk - fools the program into thinking it
  is accessing the disk, but instead the needed
  information has been transferred to RAM (RAM is
  much faster than disk access).

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Memory Management Concepts

• Virtual Memory
• addresses the problem of a program (or multiple
  programs) being too big to fit into the available
  RAM.
• The operating system divides the program into
  pieces.
• The pieces are stored on the hard disk.
• The pieces are retrieved into RAM as needed.
• Disadvantage This slows the system down, because
  retrieval of information from the disk is time
  consuming.

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File Management Concepts

• A file is a named collection of related data
• A file system is the logical view that an
  operating system provides so that users can
  manage information as a collection of files
• A file system is often organized by grouping
  files into directories (Folders)
• Most files, whether they are in text or binary
  format, contain a specific type of information
• For example, a file may contain a Java program, a
  JPEG image, or an MP3 audio clip
• The kind of information contained in a document
  is called the file type
• Most operating systems recognize a list of
  specific file types

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File Management Concepts
File Types

• File names are often separated, usually by a
  period, into two parts
• Main name
• File extension
• The file extension indicates the type of the file

Some common file types and their extensions
File Operations

• Create a file
• Delete a file
• Open a file
• Close a file

• Read data from a file
• Write data to a file
• Rename a file
• Copy a file
• Move a file

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File Management Concepts

• File Protection
• In multi-user systems, file protection is of
  primary importance
• We dont want one user to be able to access
  another users files unless the access is
  specifically allowed
• A file protection mechanism determines who can
  use a file and for what general purpose
• A files protection settings in the Unix
  operating system is divided into three
  categories Owner, Group, World (all users)

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File Management Concepts
Directory Trees

• A directory of files can be contained within
  another directory
• The directory containing another is usually
  called the parent directory, and the one inside
  is called a subdirectory
• The directory at the highest level is called the
  root directory
• A file system is often viewed as a directory tree
• At any point in time, you can be thought of as
  working in a particular location (that is, a
  particular subdirectory)
• This subdirectory is referred to as the current
  working directory

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Example Directory Tree in Windows
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Path Names

• A particular file is identified by specifying
  that files path, which is the series of
  directories through which you must go to find the
  file
• An absolute path name begins at the root and
  specifies each step down the tree until it
  reaches the desired file or directory
• A relative path name begins from the current
  working directory
• Examples of absolute paths
• C\Program Files\MS Office\WinWord.exe
• C\My Documents\letters\applications\vaTech.doc
• C\Windows\System\QuickTime
• Suppose the current working directory is
• C\My Documents\letters
• Then the following relative path name
• applications\depaul.doc
• Corresponds to the absolute path
• C\My Documents\letters\applications\depaul.doc

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Disk Scheduling

• File systems must be accessed in an efficient
  manner
• As a computer deals with multiple processes over
  a period of time, a list of requests to access
  the disk builds up
• The technique that the operating system uses to
  determine which requests to satisfy first is
  called disk scheduling

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Disk Scheduling

• First-Come, First-Served Disk Scheduling
• In FCFS, we process the requests in the order
  they arrive, without regard to the current
  position of the heads
• The shortest-seek-time-first (SSTF)
  disk-scheduling
• moves the heads the minimum amount it can to
  satisfy any pending request
• SCAN Disk Scheduling
• An elevator is designed to visit floors that have
  people waiting. Elevator moves from one extreme
  to the other (top of the building to the bottom),
  servicing requests as appropriate.
• The SCAN disk-scheduling works in a similar way,
  except instead of moving up and down, the
  read/write heads move in toward the spindle, then
  out toward the platter edge, then back toward the
  spindle, and so forth.

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System Software - Utility Programs

• Backup utility
• program which makes a duplicate copy of the
  information on your hard disk
• Data-recovery utility
• program which restores data that has been
  physically damaged or corrupted
• Antivirus software
• program that scans hard disks, floppy disks, and
  memory to detect viruses
• Data compression utility
• program which removes redundant elements, gaps,
  and unnecessary data from a computers storage
  space so that less space (fewer bits) is required
  to store or transmit data
• Disk cleanup utilities
• Detect remove unnecessary files
• Detect correct disk problems

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System Software - Utility Programs

• Fragmentation - the scattering of portions of
  files about the disk in nonadjacent areas, thus
  greatly slowing access to the files
• Defragmenter utility - program that finds all the
  scattered files on your hard disk and reorganizes
  them as contiguous files

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Development Software

• Computers can only understand instructions that
  are in machine language
• Machine language instructions are binary encoded
  operations that make up a program
• Programmers, however write programs in a
  high-level language, not in binary
• A special program, called a translator needs to
  be used to convert the high-level language source
  code into binary machine code that the computer
  understands. The machine code program is called
  the object program.
• Two types of translators
• Compilers translate the whole source code into
  machine code in one step. After the translation,
  the machine code can be executed as a single
  program.
• Interpreters translate and execute the source
  code one statement at a time. The processing is
  done interactively.

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Development Software
The Compilation Process