Operating Systems Quiz

Operating Systems Overview

• Operating systems act as intermediaries between users and computer hardware.
• Primary goals include: executing user programs, simplifying problem-solving, enhancing user experience, and efficiently using hardware.
• Key components of computer systems: hardware, operating system, application programs, and users.

Topic Coverage

• What Operating Systems Do
• Computer-System Organization
• Computer-System Architecture
• Operating-System Structure
• Operating-System Operations
• Process Management
• Memory Management
• Storage Management
• Protection and Security
• Distributed Systems
• Special-Purpose Systems
• Computing Environments
• Open-Source Operating Systems

What is an Operating System

• A program that acts as an intermediary between a user and computer hardware.
• Operating systems strive to execute user programs and make problem-solving easier, to make the computer system convenient to use, to use computer hardware efficiently,

Computer System Structure

• A computer system comprises four fundamental components:
  • Hardware, which provides fundamental computing resources (CPU, memory, I/O devices).
  • Operating system, which manages and coordinates the use of hardware among applications and users.
  • Application programs define how system resources are used for tasks, examples are word processors, compilers, web browsers, database systems and video games.
  • Users, which are individuals or machines that utilize computer systems.

Four Components of a Computer System

• Users interact with the operating system through application programs.
• The operating system sits atop the hardware, managing its utilization.

Operating System Definition

• An operating system is a resource allocator, managing all available resources and mediating requests among competing tasks.
• An operating system is also categorized as a control program responsible for controlling programs to prevent errors.

Operating System Definition (Cont...)

• The kernel is the one program running at all times on the computer.
• Other programs are either system programs (supplied with the OS) or application programs.

Computer System Organization

• Computer systems typically consist of one or more CPUs connected via a common bus to shared memory and I/O devices.

Computer-System Operation

• I/O devices and the CPU can operate concurrently.
• Each device controller handles a specific device type.
• Device controllers possess local buffers for data transfer to/from main memory.
• I/O transfers occur between devices and buffer storage, then to/from main memory
• Device controllers signal the CPU when operations are complete through interrupts.

Computer Startup

• The bootstrap program, stored in ROM or EEPROM (firmware), initializes system components upon power-up or reboot.
• Initialisation includes CPU registers, device controllers and memory contents.
• The bootstrap program loads the operating system kernel and starts executing.

Common Functions of Interrupts

• Interrupts transfer control to the interrupt service routines.
• Interrupt vectors contain addresses of interrupt service routines.
• The interrupt architecture saves the interrupted instruction address.
• Incoming interrupts are disabled during processing to avoid loss.
• Traps are software-generated interrupts caused by errors (like divisions by zero) or by user requests (system calls).
• Operating systems often depend on interrupts to respond to events.

Interrupt Handling

• The OS saves CPU state (registers & program counter) upon an interrupt.
• Special code segments handle different interrupt types.

I/O Structure

• After I/O begins, control returns to the user program without waiting for completion.
• System calls allow the user to request I/O and wait for completion.
• Device-status tables track I/O devices (type, address and state).
• The operating system modifies the device-status tables and schedules interrupts when relevant.

Direct Memory Access Structure

• High-speed devices (that can maintain memory speeds) use DMA
• Device controllers can transfer blocks of data directly to/from main memory without CPU intervention.
• DMA generates only one interrupt per block instead of one per byte.

Storage Structure

• Main memory is the only storage device directly accessible to the CPU during operational use.
• Programs and data cannot reside permanently in main memory due to limitations and volatility.
• Secondary storage (like magnetic disks) extends main memory, offering non-volatile capacity, and logical organization.
• Disk controllers interact between the computer and storage devices.

Storage Hierarchy

• Storage systems are organized hierarchically by speed, cost, and volatility.
• Faster storage is often more expensive; slower is more budget-friendly.

Storage-Device Hierarchy

• Storage devices are arranged in a hierarchy based on speed and cost.

Caching

• Caching copies information from slower storage to faster storage, for temporary operational use.
• Faster storage (cache) is checked first for requested information; if found, it's used; if not, data is copied from main memory to cache then used.
• Cache management is done with defined policies ( cache size, replacement policies).

How a Modern Computer Works

• The CPU executes instructions, manages data movement between cache, main memory and I/O devices, and handles interrupts.

Computer-System Architecture

• Modern systems use a single, general-purpose processor, along with special-purpose processors.
• Multiprocessors (parallel systems) are tightly coupled systems providing advantages like throughput increase, and graceful degradation (fault tolerance).
• Two common types: Asymmetric and Symmetric Multiprocessing (SMP).

Symmetric Multiprocessing Architecture (SMP)

• SMP involves multiple CPUs sharing a common memory space.

A Dual-Core Design

• A detailed layout depicting the components of a dual-core system.

Distributed Systems

• Distributed computing distributes tasks among multiple processors, which do not share a clock or memory.
• Communication occurs via networks, with diverse processors called nodes.

Distributed Systems (contd.)

• Resources like software, data, and hardware are shared among nodes. Processes communicate and exchange information.

Clustered Systems

• Clusters are a type of distributed system composed of multiple independent machines coupled together.
• Sharing storage via storage area networks (SAN) provides high-availability.

Clustered Systems (contd.)

• Asymmetric clustering uses one machine in standby mode while others work; the hot standby takes over when the active server fails.
• Symmetric clustering involves multiple nodes working and monitoring each other concurrently. Clusters also facilitate high performance computing (HPC).

Operating System Structure

• Multiprogramming is used to keep CPU and I/O devices busy at all times.
• Jobs (code and data) are organized so the CPU always has a task to run. A subset of total jobs gets loaded.
• Job scheduling is used by the OS to switch between jobs.

Operating System Structure (Cont.)

• Timesharing allows users to interact with each job. Short response times are needed.
• Multitasking is a logical extension of timesharing.
• If a process is too large to fit in memory, swapping moves them in and out, allowing virtual memory.

Memory Layout for Multiprogrammed System

• A diagram illustrating how a multiprogrammed system utilizes memory space, including the operating system and multiple jobs.

Operating-System Operations

• The OS responds to errors or requests via hardware interrupts and software traps.
• Key operations include process management (like preventing infinite loops and process modification).
• Dual-mode operation (user mode and kernel mode) is used by the OS to protect itself and hardware components.