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CSCI 423 EXAM 1

QuestionAnswer
What is an Operating System (OS)? A program that acts as an intermediary between the user and computer hardware
What are the three main goals of an OS? Execute user programs and make solving problems easier Make the system convenient to use Use hardware efficiently
What are the four components of a computer system? Hardware Operating System Application Programs Users
From a user’s perspective, what does an OS provide? Convenience, ease of use, performance, and fairness on shared systems.
From a system perspective, what is the OS? A resource allocator and control program.
Why is there no universal definition of an OS? Because definitions vary (e.g., “everything a vendor ships” vs. “the one program always running”).
What is always running on a computer? The kernel.
What are system programs? Programs that provide services to applications but are not the kernel.
What are application programs? Programs that perform specific user tasks.
What is the first program that runs when a computer powers on? The bootstrap program.
Where is the bootstrap program stored? In ROM or EPROM (firmware).
What does the bootstrap program do? Initializes hardware Loads the OS kernel Starts execution
What is an interrupt? A signal that causes the CPU to stop current execution and handle an event.
What happens when an interrupt occurs? Save address of interrupted instruction Use interrupt vector Transfer control to interrupt service routine (ISR)
What is an interrupt vector? A table containing addresses of interrupt service routines.
What is a trap? A software-generated interrupt (exception).
Give an example of a software interrupt. System call, divide-by-zero error.
Give an example of a hardware interrupt. Keyboard input, mouse click, disk completion.
Why is the OS called interrupt-driven? Because it waits for interrupts to determine what to do next.
What is caching? Copying data from slower storage to faster storage temporarily.
Why is cache checked first? It is faster than main memory or disk.
Why is cache smaller than main storage? Faster memory is more expensive.
Is RAM volatile or nonvolatile? Volatile (data lost when power off).
Are disks and SSDs volatile? No, they are nonvolatile.
What is the storage hierarchy (fastest → slowest)? Registers → Cache → RAM → SSD → Disk → Tape.
Why are higher levels more expensive? They are faster.
What manages I/O devices? Device controllers.
What provides a uniform interface to devices? Device drivers.
What is interrupt-driven I/O good for? Small transfers.
What is DMA? Direct Memory Access — large transfers without CPU involvement.
Why is DMA efficient? CPU remains free for other tasks.
What defines a single-processor system? One general-purpose CPU.
Are special-purpose processors considered separate CPUs? No.
What is a multiprocessor system? Two or more CPUs working together.
Advantages of multiprocessor systems? Higher throughput Lower cost Higher reliability
What is Asymmetric Multiprocessing (AMP)? One boss CPU controls worker CPUs.
What is Symmetric Multiprocessing (SMP)? All CPUs are equal and share memory.
Which type do modern OSs use? SMP (Windows, Linux, macOS).
What is a multicore system? Multiple cores on one chip.
Advantage of multicore systems? Faster communication and lower power.
What is UMA? Uniform Memory Access — equal access time.
What is NUMA? Non-Uniform Memory Access — some memory slower.
What is a cluster system? Multiple independent computers connected via network.
Why use clusters? High availability and high performance.
What is asymmetric clustering? One active node, one standby.
What is symmetric clustering? All nodes active.
What is a Beowulf cluster? A Linux cluster built from inexpensive hardware.
What is multiprogramming? Keeping multiple jobs in memory.
Why does multiprogramming improve CPU utilization? CPU switches jobs when one waits for I/O.
What is time sharing? Extension of multiprogramming for interactive use.
Difference between multiprogramming and time sharing? Multiprogramming = maximize CPU efficiency Time sharing = fast interactive response
What is a process? A running program.
What is job scheduling? Choosing which jobs enter memory.
What is CPU scheduling? Choosing which job runs next.
What is memory management? Managing multiple jobs in memory safely.
What is virtual memory? Allows programs to run without being fully in RAM.
Why is virtual memory useful? Allows programs larger than physical memory.
What are the two CPU modes? User mode and Kernel mode.
What is the mode bit? A bit indicating current mode (0 = kernel, 1 = user).
What are privileged instructions? Instructions allowed only in kernel mode.
Why are privileged instructions restricted? To protect the OS and other programs.
What is a system call? A request from a user program to the OS.
What happens during a system call? Switch to kernel mode OS validates request Executes service Returns to user mode
What happens on illegal memory access? Trap to OS.
What may the OS do with a faulty program? Terminate it and generate memory dump.
Why does the OS use a timer? Prevent infinite loops.
What happens when timer expires? control returns to OS.
Are timer instructions privileged? Yes.
How does OS stop a user from running privileged instruction? Dual-mode operation + trap to kernel.
How does OS stop infinite loops? Timer interrupt allows OS to regain control.
Why does multiprogramming increase efficiency? CPU is never idle — runs another job while one waits.
What is the main goal of an OS? Execute user programs and make problem-solving easier.
What are the two main roles of the OS? Resource allocator and control program.
Why is symmetric multiprocessing better than asymmetric? No single point of failure and better load balancing.
Created by: user-1979725
 

 



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