Operating Systems Overview Quiz

Operating Systems: CoSc 3081

• Course name: Operating Systems
• Course code: CoSc 3081
• Lecture date: February 3, 2025

Chapter One: Introduction to Operating Systems

• An operating system acts as an intermediary between the user and the computer hardware
• Operating system goals include executing user programs and making problem-solving easier
• It makes the computer system convenient to use and efficiently utilizes computer hardware
• It's a resource allocator, managing all resources and deciding between conflicting requests for efficient and fair resource use
• It's a control program that controls the execution of programs to prevent errors and improper use of the computer
• Kernel is the one program running at all times and the first layer of software loaded into computer working memory
• The kernel acts as an interface between the user, computer software, and hardware resources, providing a software platform for other programs to run.
• Other components are system programs (ships with the operating system) and application programs

Computer System Structure

• Components of a computer include users (machines/persons/computers), application programs (special software solving user problems), operating systems (controls and coordinates hardware use among various users & applications), and computer hardware (I/O, memory, CPU)
• Parts connect via a common bus for access to shared memory.

Computer System Organization

• One or more CPUs, device controllers connect through a common bus for access to shared memory
• Concurrent execution of CPUs and devices compete for memory

Computer-System Operation

• I/O devices and the CPU can execute concurrently
• Each device controller is in charge of a particular device type
• Each device controller has a local buffer
• CPU moves data between main memory and local buffers
• I/O is from the device to the controller's local buffer
• Device controller informs the CPU when its operation is finished via an interrupt

Computer Startup

• Bootstrap program is loaded at power-up or reboot
• Typically stored in ROM or EEPROM (firmware within computer hardware)
• Initializes all aspects of the system
• Loads operating system kernel and starts execution

Interrupts

• Interrupts interrupt the normal sequence of execution, improving processing efficiency
• Allow the processor to execute other instructions while an I/O operation is in progress
• A process suspension caused by an external event (such an interrupt) allows for resuming the process in an orderly fashion
• Interrupt handler is a program determining the nature of the interrupt and performing needed actions in response
• Control is transferred to the handler, which is generally part of the operating system

Common Functions of Interrupts

• Interrupts transfer control to the interrupt service routine through the interrupt vector (containing service routine addresses)
• Interrupt architecture saves the address of the interrupted instruction
• Incoming interrupts are disabled while another interrupt is processed to avoid a lost interrupt
• A trap is a software-generated interrupt caused by an error or user request
• Operating systems are interrupt-driven

Operating System Structure

• Multiprogramming is needed for efficiency
• A single user cannot keep the CPU and I/O devices busy at all times
• Multiprogramming increases CPU utilization by organizing jobs (code and data) so the CPU has jobs to execute
• Subset of total jobs is kept in memory; one job selected is run via job scheduling
• When a job waits (e.g., for I/O), OS switches to another job

Operating System Structure (Continued)

• Timesharing (multitasking) extends multiprogramming by frequently switching among jobs.
• The switch frequency creates an interactive computing environment
• Users provide instructions to the OS or program via an input device, while waiting for immediate results on an output device
• Response time should typically be <1 second.
• Such systems use minimal CPU time per user due to short time intervals for commands/actions
• Enables simultaneous user use

Operating-System Operations

• Interrupt driven by hardware or software requests (exception or trap)
• Processes like division by zero, infinite loops, modifications, and other issues are handled and prevented
• Dual-mode operation (monitor/user) protects the OS and other system components
• User mode: execution done on behalf of a user
• Monitor mode: execution done behalf of the operating system

Transition from User to Kernel Mode

• Timer prevents infinite loops/resource hogging
• OS decrements timer counter, generating an interrupt when counter reaches zero.
• This sets up before scheduling process control or termination of a program exceeding allotted time

Computing Environments

• Collection of computer hardware, software machines, and networks supporting electronic information processing for computational problems
• Traditional environments, Client-Server environments, Peer-to-Peer (P2P) environments, Web-based environments

Computing Environments (Continued)

• Traditional: PCs connected to network, terminals connected to mainframe or minicomputers with batch & timesharing capabilities.
• Now, networked and remote access use portals.
• Home networks were once single systems, now often firewalled and networked.

Computing Environments (Continued)

• Client-Server: Smart PCs replace dumb terminals, with servers responding to client requests.
  • Compute server handles client service requests (e.g., database).
  • File server processes client file requests (storage & retrieval).

Computing Environments (Continued)

• Peer-to-Peer (P2P): Distributed system where all nodes (peers) are considered equal, able to act as clients or servers.
  • Nodes must register services with a central lookup service on the network, or broadcast requests for service.

Computing Environments (Continued)

• Web-based: Ubiquitous PCs and devices networked to support web access. New device categories manage web traffic among similar servers (load balancers). Modern OS like Linux and Windows XP can act as clients or servers.

Special Purpose Systems

• Real-time embedded systems: Fixed constraints for operation, embedded computers in various devices (home, industry). Devices often monitor and control (e.g., scientific experiments, industry processes, or appliances)
• Multi-media systems: Extends conventional systems to handle multimedia data (e.g., video, audio, text). Includes personal digital assistants (PDAs) like pocket PCs and palm PCs and cellular telephones. Specialized embedded OS may be used.

Operating-System View

• Functional view (what it does): Program execution/handling, I/O operations, file/system management, and communications between users or processes. Exception handling, protection and resource allocation are also functions.
• Component view (designers view): Processes (programs in execution), storage management (main memory, secondary storage), and I/O management (device drivers, files & systems)

Operating-System View (continued)

• Component view (Continued): Networking (support for communication), protection (controlling access to resources)

Services View

• Interpreters: user interface and interaction.
• System calls: programming interface to the OS (commonly coded via APIs rather than direct system calls). Popular APIs include POSIX, Windows.
• System programs (provide convenient environment): includes commands, compilers, editors, etc.

Services View (continued)

• System programs further break down into support functions: file manipulation, status information, file modification, programming language support, program loading/execution, communications, application programs

Shell: an OS Interface

• Program sitting on top of the kernel; command interpreter; interactive access to system calls.
• Has its own programming ability as well.
• Simple programming languages, popularized through UNIX.

Structure View: Simple Structure

• MS-DOS: Designed for efficient functionality in limited space but with a less structured approach, not divided into modules, and interfaces/levels are less separated. It's thus more vulnerable to errors or malicious programs.

Structure View: Layered Approach

• Operating system divided into layers (e.g., layers on top of each other).
• Lowest layer is hardware, top layer is user interface.

Structure View: Layered Approach (Unix)

• UNIX OS consists of the kernel (everything below the system call interface and above the physical hardware) and System programs.
• Kernel provides file systems, scheduling, memory, and other operations.

Structure View: Layered Approach (continued)

• UNIX System Structure: Includes components like shells, commands, compilers, system calls, signals, and different device drivers (e.g., terminal) that interact with hardware (e.g., disks and tapes, memory controllers).

Structure View: Microkernel

• Moves kernel functions (previously kernel-based) to user space.
• Kernel-user communication occurs via explicit message passing.

Structure View: Microkernel (continued)

• This structure is easier to extend, port and secure because many tasks occur outside kernel mode.

Structure View: Modules

• Modern operating system kernels often use modules for core components.
• Communication occurs through well-defined interfaces in an object-oriented approach
• Each module is loadable, making the kernel more flexible.

Structure View: Virtual Machines

• A virtual machine emulates a hardware environment. Operating system kernel is used as though for a whole machine (the virtual one).
• Isolation keeps resources separate between them.
• Is a useful tool for research and development; virtual environment doesn't interfere with the real OS.

Structure View: Virtual Machines (continued)

• The virtual machine concept is complex, requiring resource emulation.

Structure View: Virtual Machines (continued)

• This structure uses a virtualization layer, with guest operating systems (e.g., Windows or Linux) and applications running on it.

The Java Virtual Machine

• A virtual machine for executing Java programs
• Java programs compile into byte codes that are executed by the interpreter

Reading Assignments

• Review OS from different views like service and functional.
• Explore system programs & their role, identifying various types
• Analyze cache memory, highlighting its advantages.
• Understand and categorize OS functionalities. Analyze users' interfaces in OS, program execution, I/O, file systems, operations for communications, and various types of resources like file manipulation, status information, file modification support, programming loading/execution, and other OS communications and applications.
• Review different types of operating systems, their characteristics(e.g. serial processing, simple batch systems, multiprogrammed batch systems, timesharing systems), and examine functions in detail.

Recommended Websites

• Sources of operating system information and resources, including discussions & reviews