chapter 4

• An operating system connects the user with the machine (computer, phone, etc.)
• It controls the allocation and use of the physical part of the computer (Hardware)
• An operating system acts as a conductor listening to requests from the user to put everything in place to respond
• The main functions of an operating system are to manage resources of the machine efficiently
• There are dozens of different operating systems in the market, such as Windows, Mac OS, Linux, and Symbian OS
• Operating systems provide general services that facilitate the creation of application software
• Operating systems allow running programs, reading and writing information, manipulating files, communicating between computers, and detecting errors
• The operating system protects resources against unauthorized use and resolves conflicts when multiple users request the same resource
• When an error occurs, the operating system softens its impact on the computer system and may retry the operation, stop the faulty program, or report the problem to the user
• The Basic Input Output System (BIOS) is a configuration program that starts the computer and recognizes the main hardware components
• BIOS performs tests on hardware components and allows the system to boot
• The operating system manages memory, displays data, sends data to devices, responds to inputs, and reads and writes data to storage devices
• Multi-tasking operating systems allow sharing CPU time for multiple programs to run simultaneously
• Multi-processor systems organize the execution of applications on different processors
• Multi-user systems allow different people to work with a computer at the same time
• File systems organize data on storage mediums like hard disks, floppy disks, and USB keys
• Files are grouped in directories, organized in a tree structure, and identified by names with properties like read/write access and owner
• Disk geometry includes concentric tracks, cylinders, and sectors for data tracking
• Disk capacity is determined by the size of tracks, cylinders, and trays
• HDDs and SSDs both boot systems, store applications and personal files, but have different features
• HDDs are essentially metal trays with a magnetic coating
• SSDs store data on interconnected flash memory chips that hold the data permanently
• Advantages of SSD over HDD:

  • SSD has better performance when many small files are used
  • SSD has faster access time compared to HDD
• Temperature, noise, and strength advantages of SSD over HDD:

  • SSD hardly heats up during operation
  • SSD remains silent while HDD produces noise, especially during random access to a large number of files
  • SSD is more solid and resistant to shocks compared to HDD
• Storage capacity and price advantages of HDD over SSD
• A file is a series of sectors and the order is essential

  • A directory is a collection of file names with access to the list of their sectors, and a directory is itself a file stored in a series of sectors
• • Third-generation computers introduced integrated circuits, IBM 360 series, DEC PDP-8, and Data General Nova with new techniques in operating systems like multiprogramming, shared memory, protection mechanisms, and examples of operating systems like MULTICS, UNIX, and Linux
  • Fourth-generation computers introduced microprocessors and popular models like Micral, Altair, Apple I and II, IBM PC, Commodore 64, Apple Lisa, and Apple Macintosh with operating systems like CP/M, MS-DOS, Macintosh, Windows, UNIX/Linux
• Comparison of early computers:

  • Moore School's Electronic Numerical Integrator And Computer was often considered the first computer with characteristics like 30 tons, 150 KW, 18000 vacuum tubes, and programming by rewiring
  • Second-generation computers included IBM 1401, 1620, 7000, and DEC PDP-1 with operating systems like FMS and IBYS
• Mobile operating systems:

  • Android and iOS lead the market with 80% and 15% market share respectively
  • Other challengers include Windows Phone 8 and BlackBerry 10
  • Challenges faced by Tizen, Firefox OS, and Ubuntu Phone in the mobile OS market
• Comparison between mobile OS:

  • Android faces fragmentation issues with different device versions
  • iOS updates are less problematic than Android
  • iOS is more closed compared to Android
  • Windows Phone supports Android applications for compatibility