Opessys

• Operating System


  A program that acts as an intermediary between the user and the computer hardware. It is able to run user programs, improves convenience when using the computer and efficiently uses computer hardware.
• Operating System


  • Provide ease of use and 'readability' to the user
  • Acts as a resource allocator and control program for the hardware of the system
  • Manages the execution of programs by the user
  • Kernel - Main program running at all times on the computer
  • System Program - separate from the kernel. Comes with the operating System
  • Application Program - all programs not associated with the operating system
• Middleware


  A set of software frameworks that allow developers to have additional capabilities when creating applications
• Parts of a Computer System Structure

  • Hardware
  • Operating System
  • Application Programs
  • Users
• Computer System Organization


  • CPUs and I/O devices connect through a common system bus which grants access to shared memory of the computer. These can run concurrently
  • CPU moves data from/to main memory from the local buffers that come from the I/O devices
  • The device controllers, individually, are able to control specific devices in the system, have local buffers and a device driver to manage it. These use interrupts to signal the end of an operation
• Interrupts


  • Operating Systems are interrupt driven
  • Interrupt Vector - Contains the addresses of all service routines
  • Interrupt Architecture - Would save the address of the interrupted instruction
  • Trap or Exception - software generated interrupt caused either by an error or user request
  • Interrupt Handling - Separate segments of code that determine the action taken when encountering a certain interrupt
• I/O Handling Methods


  • Control returns to user program only upon completion
  • Control returns to user program without completion
• System Call


  Request by the system to the Operating System to allow the user to wait for I/O completion
• Types of Storage


  • Main Memory - Random Access Memory (RAM) and Dynamic Random Access Memory (DRAM)
  • Secondary Storage - Hard Disk Drives (HDD)
  • Non-Volatile Memory (NVM)

  
• Hard Disk Drives (HDD)


  • Surface of the disc are divided into tracks that are divided into sectors
  • Disc Controller - Determines the logical interactions between device and computer
• Non-Volatile Memory (NVM)


  Known to be faster than hard disks. Growth recently due to the capacity and performance.
• Direct Memory Access


  • Device controller is able to transfer blocks of data from buffer storage directly to main memory without CPU intervention
  • One interrupt per block is generated
• Operating-System Operations


  • Bootstrap Program - Code that is used to initialize the system and power the Kernel
  • System Daemons - Services that are provided outside of the Kernel
  • Kernel Interrupt - Hardware interrupt is triggered by one of the devices followed by a software interrupt (either software error or system call)
• Multiprogramming


  • Batch System - Organization of the code and data for the CPU to always be busy. All total jobs are listed and kept in memory. Job Scheduling - When a job is selected out of the queued jobs by the OS
  • Timesharing - Extension of the Batch Systems capable of having the CPU switch jobs frequently so that the user is able to interact with each of the jibs happening. Response time - Less than one (1) second. Process - At least one (1) program being executed in memory. CPU Scheduling - When the system has several jobs queued to run. Swapping - When processes do not fit in the memory and thus need to be moved in and out. Virtual Memory - allows the execution of processes without the need to be reliant on the physical memory

  
• Dual-mode Operation


  • Allows the OS to rely on both the user and kernel
  • Mode Bit - Provided by hardware. Helps in identifying when the system is running based on the user or kernel code
• Timer


  Used in order to prevent infinite loops from occurring by interrupting the ongoing process after a certain criteria was reached
• Process


  Program in execution. Unit of work in a system. Active Entity
• Program


  Passive Entity
• Process Resources


  • CPU
  • Memory
  • I/O
  • Files
  • Initialization Data

  
• Single-threaded Process


  Has one program counter for location of next instruction to execute sequentially
• Multi-threaded Process


  One (1) program counter per thread. Usually has many processes operating at the same time on one or more CPUs
• Operating System in Process Management

  • User and System process creation and deletion
  • Process suspension
  • Providing mechanisms for synchronization, communication and deadlock handling
• Memory Management Activities


  • Optimizing CPU utilization and user response
  • Tracking which part of the memory is used
  • Deciding what process and data to be moved in and out of the memory
  • Memory Space organization and allocation

  
• File-system Management


  • Creating and deleting files and directories
  • Primitives to manipulate files and directories
  • Mapping files onto secondary storage
  • Backup files onto stable storage devices
• File


  Abstract physical properties to logical storage units. Organized into directories
• Mass-Storage Management


  • Mounting and connections
  • Free-space management
  • Storage Allocation
  • Disk Scheduling
  • Partitioning
  • Protection

  
• Caching


  Important principle, performed at many levels in a computer where information in use is copied from slower to faster storage temporarily
• I/O Subsystem Responsibilities


  • Buffering - Storing data temporarily while being transferred
  • Caching - Storing parts of data in faster storage for performance
  • Spooling - The overlapping of output of one job with input of another
  • Device-driver interface
• Protection and Security


  • Protection – any mechanism for controlling access of processes or users to resources defined by the OS
  • Security – defense of the system against internal and external attacks
  • User Identities - including name, number and assigns a User ID associated with all the files that the user has control over
  • Group Identifier - Allows set users, defined by a Group ID, to control files
  • Private Escalation - Allows a user to change to a more effective ID with more rights
• Virtualization


  • Emulation - Used when source CPU type different from target type (i.e. PowerPC to Intel x86)
  • Virtualization - OS natively compiled for CPU, running guest OSes also natively compiled. Includes Virtual Machines, which can run natively where they are also the host
• Network Types


  • Local Area Network (LAN)
  • Wide Area Network (WAN)
  • Metropolitan Area Network (MAN)
  • Personal Area Network (PAN)
• Network Operating System


  Provides features between systems across networks which allows systems to exchange messages
• Multiprocessor Systems


  • Advantages are an increased throughput, Economies of scale and Increased Reliability
  • Asymmetric Multiprocessing - Each processor is assigned a specific task
  • Symmetric Multiprocessing - Each processor performs all tasks
• Dual-Core


  Multi-chip and Multicore. System containing all chips and chassis containing multiple separate systems.
• Clustered Systems


  • Like multiprocessor systems, but multiple systems working together usually sharing storage through a storage-area network (SAN)
  • Asymmetric Clustering - Has one machine in standby mode
  • Symmetric Clustering - Has multiple nodes running applications while monitoring one another
  • Parallelization is required as written by applications. While some having distributed lock managers (DLMs)
• PC Motherboard is a good example of a fully-functioning computer once its slots such as processor, DRAM, PCIe (GPU and SSD), and Input/Output connectors are populated
• Types of Computer Environments

  • Traditional
  • Mobile
  • Client Servers
  • Peer to Peer
  • Cloud Computing
  • Real-Time Embedded Systems
• Client Servers


  Terminals that are used to respond to client requests and a system that is able to store client information through a database
• Compute-Server System


  Provides an interface to client request services
• File-Server System


  Provides an interface for clients to store and retrieve files