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Active Recall

Updated 4 Oct 2026

I'll create a set of active recall questions and answers about operating systems based on your document:

  • What are the four layers of a computer system?

    • Computer hardware (CPU, RAM, etc.)
    • Operating system (OS)
    • Application programs (MS Word, Pages, etc.)
    • Users

  • What are the two main roles of an operating system?

    • Resource/Hardware Management: Managing and allocating hardware resources efficiently and fairly
    • Services: Acting as an interface between applications/users and hardware

  • What happens when we run a program?

    • The hard disk application converts into a set of machine instructions (process)
    • These instructions are stored in main memory (RAM)
    • The CPU fetches and executes the instructions, displaying the program output

  • What is a process?

    • A process is an executing instance of a program

  • What are the two stages of CPU execution in the basic instruction cycle?

    • Fetch Stage: The CPU fetches an instruction from memory
    • Execution Stage: The CPU decodes and executes the instruction

  • What is the purpose of hardware interrupts?

    • Increases CPU utilization by preventing idle time
    • Allows the CPU to work on other tasks while I/O operations are in progress
    • Signals the CPU when an I/O operation is complete

  • What are the types of storage in a computer system, from fastest to slowest?

    • Registers and cache (fastest)
    • Main memory (RAM)
    • Secondary storage (HDD, SSD)
    • Tertiary storage (CD-ROMs, tapes, etc.) (slowest)

  • What is Direct Memory Access (DMA) and why is it important?

    • DMA allows a DMA controller to handle data transfer between I/O devices and memory without CPU intervention
    • It frees up the CPU for other tasks, improving efficiency

  • What is the difference between multiprogramming and multitasking?

    • Multiprogramming: The capability to load multiple processes and store them in main memory
    • Multitasking (Time-Sharing): The capability to run multiple processes by using time-sharing, where the CPU frequently switches between processes

  • What are the two modes of operation in a dual-mode system?

    • Kernel Mode (0): The OS runs with full control over the computer and can execute all instructions
    • User Mode (1): User programs run with restrictions on privileged instructions

  • What is a system call?

    • A CPU instruction that requests the OS to perform a privileged task
    • Allows a user program to request privileged tasks from the OS

  • What triggers context switching between processes?

    • Hardware Interrupts: Signals sent by an I/O controller
    • Software Interrupts (Traps): Triggered by errors or system calls
    • Timer Interrupts: To prevent indefinite execution of a single process

  • What are the three main OS structures discussed?

    • Monolithic Structure: OS as one large program in a single address space
    • Layered Structure: OS divided into multiple layers with defined interfaces
    • Microkernel Structure: Only essential components in the kernel, other services in user space

  • What is the advantage of the modular approach in OS design?

    • Changes in one part won't affect the whole system
    • Easier to update and modify components
    • Better maintainability and debugging

  • What are the main resource management responsibilities of an OS?

    • Process Management
    • Memory Management
    • File Management
    • Storage Management
    • I/O System Management
    • Protection and Security