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Computer Systems 1 Fundamentals of Computing


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  • 1. Computer Systems 1 Fundamentals of Computing Operating Systems
  • 2. CS1 - Week 22
    • Introduction to the OS
    • OS Fundamentals
      • Processes
      • Memory
      • Files
      • I/O
  • 3. The Operating System (OS)
    • Manages the hardware and software resources of the system
    • Resources
      • Processor
      • Memory
      • Disk space, etc.
    • Allows applications to deal with the hardware without having to know all the details of the hardware
  • 4. Operating Systems Hardware Operating System User Application Application Application User User
    • The OS acts a a ‘shell’ around the hardware.
    • The applications software need an OS to work, and users need the applications software to interact with the hardware via the OS.
  • 5. Types of OS
    • Real-Time Operating System (RTOS)
      • Fast Response (‘Real Time’ / Instant)
      • Used to control machinery and industrial systems
      • Usually Poor HCI
    • Single-User, Single Task
      • One user can do one thing at a time
      • Useful for low spec systems
    • Single-User, Multi-Tasking
      • One user can perform many tasks at a time
      • Common for current PC systems
    • Multi-User
      • Many users can use the computer's resources simultaneously
      • OS balances resources allocation against users and tasks
      • N.B- A machine on a network is not necessarily multi-user!!!
  • 6. OS Generic Structure
    • Kernel
    • Memory & Process Management
    • Input / Output
    • File System
    • User Interface
  • 7. The Kernel
    • Heart of the OS
    • Provides secure access to the computer hardware
    • Low-level software / hardware transfer
    • Manages resource availability / usage
    • A kernel includes
      • Interrupt handler
        • Handles all requests for kernel service
      • Scheduler that
        • Decides how and which programs share the kernel processing time
      • Supervisor
        • Gives use of the computer to each process when required
  • 8. Types of kernels
    • Monolithic Kernel
      • Runs most of its services in the kernel workspace
      • Error prone due to the amount of tasks in the kernel itself
      • Used in most Linux systems
    • Microkernel
      • Runs most services - like networking, filesystem, etc. - in user space
      • More stable, but more complex designs
    • Hybrid (Modified Microkernel)
      • Microkernels that have some "non-essential" code in kernel space in order for that code to run more quickly.
      • Windows NT/2000 and Macintosh OS X use hybrid kernels
  • 9. Process Management
    • Process
      • A single sequence of operation(s)
      • The basic unit of software the operating system deals with in scheduling the work done by the processor
      • Not the same as an application
        • An application can contain multiple processes
    • Process has some key attributes
      • Process ID (PID)
      • Priority Level
      • Pointers to upper and lower bounds of memory allocated
      • Status of all I/O devices needed
  • 10. Process Management
    • CPU can only do one thing at a time
      • If a process wants to use the CPU it must tell the CPU
        • Interrupts or Polling
    • To give the appearance multi-tasking, the quickly OS switches between different processes
      • This function is performed by a process scheduler
    • Schedulers decide what process should run, when , and for how long
    • Scheduling decision factors
      • Priority
      • Resources needed
      • Resources used to date
      • Waiting time to date
  • 11. Memory Management
    • Provide memory space to enable multiple processes to be executed at the same time
    • Give satisfactory level of performance for users
    • Protect each process
      • Don’t get data mixed-up between processes
    • Enable sharing of memory between processes
      • More dynamic & efficient use of the memory resources
    • Make addressing of memory transparent to programmers
    • Provides Virtual Memory
      • Extra memory, larger than the physical allocation
      • Done by storing portions of data to backing storage
  • 12. Input / Output Need more input….
    • Devices use an I/O sub-system of a computer use to communicate
      • Communication carried out via registers
    • I/O devices use interrupts to signal to the CPU that a task has been completed
      • IRQ – Interrupt ReQuests.
      • Each device has a unique IRQ
    • On ISA buses, data can be sent from the I/O controller to memory, bypassing the the CPU
      • This is DMA (Direct Memory Access)
  • 13. Input / Output
    • Input / Output Control System (IOCS)
      • The part of the O/S that deals with I/O activity
      • Deals with requests and routes to and from devices
    • Device Driver
      • A software module which manages the communication with, and control of, a specific I/O device
      • Interprets requests from the application to specific commands to the I/O device
    Application Program Input-output Control System (IOCS) Device Driver Device Controller I/O Device System Calls I/O Bus } Operating System
  • 14. File System
    • File can be stored data, although programs and folders are also considered files at a low level
    • OS knows nothing about file structure
      • Applications can interpret file data
    • File System tasks
      • Creating & deleting files
      • Storing and organising files on storage medium
    • A new file is allocated one cluster
    • As the file grows the cluster becomes filled and more clusters are assigned to the file
  • 15. File System
    • Ideally, successive file clusters should be in sequence on the disk
      • Faster access as less disk movement in required
    • Usually a disk contains many files
      • Clusters get mixed out of sequence
      • This is known as fragmentation
    • Fragmentation can reach a critical level where system performance becomes greatly reduced
    A A B A B C C B B End of file A Free cluster End of file B
  • 16. File System
    • Windows file systems are FAT
      • File Allocation Table
      • FAT16
        • Uses 16-bit value to record file properties
      • FAT32
        • Very similar to FAT16, except it uses 32-bit values
    • Linux / UNIX Use iNodes
      • Similar procedure to Windows
      • Usually 32-bit values
      • Every file has an iNode
      • OS tracks iNodes and file names
  • 17. User Interface
    • The user interface (UI) is a layer above the operating system
      • What users “see” or interact with
    • UI deals with getting user commands and providing feedback / representation
    • Two common types of user interfaces:
      • Command-Line Interface (CLI)
      • Graphical User Interface (GUI)
  • 18. Command-Line Interface
    • Textual commands
      • Either from the keyboard or from a script
    • User types a command after the computer displays a prompt character
      • For example, MS-DOS, UNIX, etc.
    • Advantages
      • Faster for skilled users
      • All options and commands available in a standard format
      • Can perform operations in a batch processing mode without user interaction
    • Disadvantages
      • Perplexes new users / Not user-friendly
      • Multiple operations made complex
      • Have to remember commands / not intuitive
  • 19. Graphical User Interface
    • Graphical representations & metaphors
    • GUIs have a number of common features:
      • Windows, Icons, Menus, Pointers (WIMP)
      • As well as buttons, toolbars, etc.
    • Advantages
      • Consistent look and feel, even across platforms
      • Commands can be executed using either mouse or keyboard
      • High levels of operation and dialog
    • Disadvantages
      • Often restrictive
      • Use more system resources / more intense
  • 20. UNIX
    • Designed by Ken Thomson of AT&T Bell Laboratories improved by Dennis Ritchie
    • Multi-user
      • More than one person suing the OS at a time
    • Multitasking
      • Each user can run more than one process
    • Platform independent
      • Runs on almost any hardware platform
    • Complex
    • Large distribution
    • User control and administration
    • Used as multiple types of server
  • 21. LINUX
    • Created by Linus Torvalds
    • Particularly aimed at PC users
    • Two parts:
      • Kernel
        • The Linux operations section
        • The UNIX part of things
      • Distribution
        • Particular flavour of Linux
    • Open source
      • Free! (more or less)
    • Many now have a windows style interface
      • Easy to get to grips with
      • Some expertise is required to become a master
    • Low hardware requirements
      • 100 MHz CPU, 12Mb RAM, 500Mb HDD
  • 22. Microsoft Windows
    • Founded by Bill Gates
    • Developed from MS-DOS
      • Microsoft Disk Operating System
        • ‘ Borrowed’ from XEROX Q-DOS
    • Windows 1.0 began life as an interface running on MS-DOS
    • GUI improved and networking capabilities added in future versions
    • Is now independent of MS-DOS
    • Many varieties available
      • Majority are multi-user and multi-task
        • Windows XP
        • Windows Server
        • Windows 2000
  • 23. Macintosh OS X
    • Rooted in a UNIX system
      • Providing all the good bits of a powerful UNIX OS
    • Super-nice GUI as front-end
      • Ease of use and interaction
    • Macintosh OS have always been pioneers in user-friendly interfaces and functionality
    • High level of accessibility
    • Scalable from first-time users to advanced
    • Seamless integration of OS and system applications
  • 24. Week 22
    • Operating System Structure & Components
      • Kernel
      • Memory management
      • Process management
      • Input / output
      • File system
      • User interface