L8 Network & Operating Systems Flashcards by Joey Pang

What are the key services an operating system provides?

• User Interface (CLI, GUI, Batch)
• Program execution
• I/O operations
• File-system manipulation
• Communication
• Error detection
• Resource allocation
• Accounting
• Protection and Security

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What types of user interfaces do operating systems typically offer?

• Command-Line Interface (CLI)
• Batch interface
• Graphical User Interface (GUI)

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What is program execution in the context of OS services?

• The ability to load and run programs in memory
• Handle normal and abnormal termination
• Manage resources for execution

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What does the operating system do in terms of I/O operations?

• Provides an interface to I/O devices
• Facilitates data exchange with files and peripherals
• Prevents direct device manipulation by users

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How does an OS facilitate file-system manipulation?

• Allows creation, deletion, reading, and writing of files
• Manages directories and permissions
• Provides search and metadata access

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Describe how OS handles communication between processes.

• Shared memory or message passing
• Inter-process or inter-system communication
• Handled via OS for data integrity and synchronization

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What is error detection in operating systems?

• Identifying and handling hardware/software errors
• Includes power failure, memory issues, invalid instructions
• OS may terminate or recover processes

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What is resource allocation in OS?

• Distribution of CPU time, memory, and I/O devices
• Done for concurrent users/processes
• May involve specific or general allocation algorithms

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What is the role of the command interpreter or shell?

• Accepts user commands and executes them
• May be part of the kernel or user-level system program
• Examples include BASH, cmd.exe

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How do batch files relate to OS?

• Scripts containing CLI commands
• Automate tasks
• Used in system diagnostics, automation, etc.

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Describe the three major APIs for system calls.

• Win32 API (Windows)
• POSIX API (UNIX-based)
• Java API (Java VM)

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How are system calls typically invoked?

• Programs use API functions
• System call number passed to OS kernel
• Kernel executes the call and returns status/result

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What are some common types of system calls?

• Process control
• File manipulation
• Device management
• Information maintenance
• Communication

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What are system programs?

• Utilities that provide a programming environment
• Examples: File managers, compilers, loaders, device drivers

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What is a process in operating systems?

• A program in execution
• Needs resources like memory, CPU, files
• Can be user or system process

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What is a process composed of?

• Text: Program code
• Stack: Temporary data
• Data: Global variables
• Heap: Dynamically allocated memory

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What are the different states of a process?

• New
• Running
• Waiting
• Ready
• Terminated

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What is the Process Control Block (PCB)?

• Data structure storing information about a process:
- Process state, program counter, CPU registers
- Scheduling info, memory info, I/O status

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When is the PCB updated?

• Whenever a process changes state
• During interrupts, scheduling, or completion of tasks

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What are the three major process scheduling queues?

• Job queue: All processes in system
• Ready queue: Processes in memory ready to execute
• Device queue: Processes waiting for I/O devices

What does the short-term scheduler do?

• Chooses next process to run
• Runs frequently (e.g., every few ms)
• Allocates CPU to processes

What is the role of the long-term scheduler?

• Decides which processes to bring into ready queue
• Runs less frequently
• Controls multiprogramming level

Differentiate between I/O-bound and CPU-bound processes.

• I/O-bound: More time in I/O, short CPU bursts
• CPU-bound: Long CPU usage, few I/O operations

What is depicted in Diagram 1?

Hierarchical structure showing user programs accessing system and application programs, which interface with the OS and hardware

Where does the operating system sit in the architecture?

* Between system/application programs and computer hardware

What are some system/application programs in the diagram?

* Compiler, assembler, text editor, database system

What is the role of the system call interface in this diagram?

* Bridges user mode and kernel mode for system calls

What happens when an application makes an `open()` system call?

* The request goes through the system call interface, kernel looks up implementation, executes it, and returns the result

What does this diagram show?

* Flow of a high-level function (`printf`) through standard C library to a system call (`write()`)

Why is the C library involved before a system call?

* It abstracts direct system call use and manages parameters

What layers are shown in this OS services model?

* User programs, user interfaces, system calls, services, OS, hardware

Which layer handles file systems and communication?

* Services layer under system calls

What regions are shown in the process memory layout?

* Text, Data, Heap, Stack

How do stack and heap grow?

* Stack grows downward, heap grows upward

What is the purpose of this comparison table?

* Shows equivalent system calls in Windows and Unix for common operations

Give a file manipulation example from both OSes.

* Windows: `CreateFile()`, Unix: `open()`

What components make up a PCB?

* State, process number, PC, registers, memory limits, open files

Why is the PCB essential for scheduling?

* Stores process-specific data needed to resume execution

What state changes are shown in the diagram?

* New → Ready → Running → Waiting → Terminated

When does a process enter the waiting state?

* During I/O wait or event wait

What does the diagram show?

* How processes move between ready and device queues

What queues are color-coded?

* Ready queue (blue), Device queue (yellow)

What is shown in the queue layout?

* Linked-list style ready/device queues with pointers to PCBs

How are PCBs connected in queues?

* Each has a pointer to the next in the linked list

What does the green star represent?

* New process entering the ready queue

What event causes a context switch?

* Interrupt or system call

What does the OS do during context switching?

* Saves current state to PCB, loads new process state

Why is context switching necessary?

* To allow multitasking by switching between processes