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Questions and Answers
What does the variable argc represent in C programs?
What does the variable argc represent in C programs?
Which of the following describes the 'Waiting' state of a process?
Which of the following describes the 'Waiting' state of a process?
What is the purpose of the Process Control Block (PCB)?
What is the purpose of the Process Control Block (PCB)?
Which of the following statements is true regarding argv in a C program?
Which of the following statements is true regarding argv in a C program?
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Which process state indicates that instructions are currently being executed?
Which process state indicates that instructions are currently being executed?
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What is the primary function of a socket in client-server communication?
What is the primary function of a socket in client-server communication?
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In which scenario are two FIFOs typically used?
In which scenario are two FIFOs typically used?
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What happens to a process when it reaches the 'Terminated' state?
What happens to a process when it reaches the 'Terminated' state?
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When using command line arguments in C, what is typically passed as the first element of argv?
When using command line arguments in C, what is typically passed as the first element of argv?
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What distinguishes a Remote Procedure Call (RPC) from a standard function call?
What distinguishes a Remote Procedure Call (RPC) from a standard function call?
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What state indicates that a process is prepared to be assigned to a processor?
What state indicates that a process is prepared to be assigned to a processor?
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Which of the following correctly identifies how a socket is represented?
Which of the following correctly identifies how a socket is represented?
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What feature is specific to the MS Windows version of named pipes compared to UNIX?
What feature is specific to the MS Windows version of named pipes compared to UNIX?
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What does the return value of wait(&wait_status) indicate on success?
What does the return value of wait(&wait_status) indicate on success?
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What is the primary use of the execlp() function?
What is the primary use of the execlp() function?
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What happens if the specified file name in execlp() includes a slash character?
What happens if the specified file name in execlp() includes a slash character?
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What character marks the end of the argument list in execlp()?
What character marks the end of the argument list in execlp()?
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Which of the following statements regarding execvp() is true?
Which of the following statements regarding execvp() is true?
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Which option indicates that exec() will search for executable files using the current environment variable PATH?
Which option indicates that exec() will search for executable files using the current environment variable PATH?
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What does the wait_status variable receive after a successful wait() call?
What does the wait_status variable receive after a successful wait() call?
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What is the main function of the 'in' variable in the bounded buffer?
What is the main function of the 'in' variable in the bounded buffer?
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In which scenario would execvp() be the preferred function to use?
In which scenario would execvp() be the preferred function to use?
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When will the consumer have to wait in a bounded buffer implementation?
When will the consumer have to wait in a bounded buffer implementation?
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Which condition describes a full buffer in the bounded buffer implementation?
Which condition describes a full buffer in the bounded buffer implementation?
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What is the primary benefit of using an unbounded buffer?
What is the primary benefit of using an unbounded buffer?
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What happens to the producer if the bounded buffer is full and cannot accommodate more items?
What happens to the producer if the bounded buffer is full and cannot accommodate more items?
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In the producer process code, what does the while loop check for?
In the producer process code, what does the while loop check for?
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Which data structure is used to implement the shared buffer in the producer-consumer scenario?
Which data structure is used to implement the shared buffer in the producer-consumer scenario?
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What guarantees that the buffer size does not exceed a specific limit in the bounded buffer system?
What guarantees that the buffer size does not exceed a specific limit in the bounded buffer system?
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Who started developing the GNU operating system?
Who started developing the GNU operating system?
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What year was the Free Software Foundation (FSF) founded?
What year was the Free Software Foundation (FSF) founded?
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Which of the following is NOT one of the four essential freedoms defined by the free software movement?
Which of the following is NOT one of the four essential freedoms defined by the free software movement?
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What does the GNU acronym stand for?
What does the GNU acronym stand for?
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What does the GPL primarily ensure?
What does the GPL primarily ensure?
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Which statement accurately reflects the meaning of 'free' in 'free software'?
Which statement accurately reflects the meaning of 'free' in 'free software'?
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What is a significant characteristic of software released under the GPL?
What is a significant characteristic of software released under the GPL?
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Which of the following describes the relationship between free software and open-source software?
Which of the following describes the relationship between free software and open-source software?
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What happens when execvp() is successful?
What happens when execvp() is successful?
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What value does execvp() return if an error occurs?
What value does execvp() return if an error occurs?
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What is typically performed by the parent process after a fork() call?
What is typically performed by the parent process after a fork() call?
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If both the parent and child processes do not invoke exec() or wait(), what occurs?
If both the parent and child processes do not invoke exec() or wait(), what occurs?
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How many times will 'bye' be displayed in the scenario where both the parent and child do not invoke exec() or wait()?
How many times will 'bye' be displayed in the scenario where both the parent and child do not invoke exec() or wait()?
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What is the result of invoking fork() two times?
What is the result of invoking fork() two times?
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What is the purpose of the exec() family of system calls?
What is the purpose of the exec() family of system calls?
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Which of the following statements about fork() is accurate?
Which of the following statements about fork() is accurate?
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Study Notes
Chapter 1: Introduction
- Operating systems (OS) are responsible for managing computer hardware and software resources;
- A computer system includes hardware components (CPU, memory, I/O devices), the operating system, application programs, and users.
- The OS controls and coordinates hardware use among applications and users. Applications define how system resources are used to solve computing problems.
- The OS is defined as "everything a vendor ships when you order an operating system", but it varies.
- Definition 2 of the Operating System is "the one program running at all times on the computer". More accurately, it's the kernel, part of the operating system.
- Everything else is either a system program (ships with the operating system but not the kernel) or an application program not associated with the operating system.
- Computer architecture deals with logical aspects of system implementation as seen by the programmer (e.g., instruction sets, instruction formats, data types, and addressing modes).
- Computer organization deals with the physical aspects of computer systems (e.g., circuit design, control signals, and memory types).
- Computer architectures like Intel/AMD X86 are often implemented in different ways across different companies.
- Multiprocessor systems, e.g., symmetric multiprocessing (SMP), use more than one processor;
- Multicore systems, which are now common, incorporate multiple processing cores on a single chip.
- Clustered systems combine multiple computers to share resources and improve performance.
Chapter 1: Computer Architecture
- Single-processor systems traditionally utilize one processor.
- Multiprocessor systems now dominate modern computers, from mobile devices to servers. These systems commonly have two or more processors, each with a single-core CPU.
- The processors often share computer bus and, sometimes, the clock, memory and peripheral devices.
Chapter 1: Multiprocessor Systems
- Symmetric multiprocessing (SMP) systems are where each CPU processor performs all kinds of tasks, including operating-system functions and user processes.
- Multicore systems have multiple processing cores inside a single chip. On-chip communication between cores is faster than communication between chips. Multicore systems consume less power than multiple single-core chips.
Chapter 1: Multiprocessor Systems (Cont.)
- Non-uniform memory access (NUMA): This approach assigns local memory to each CPU for faster access.
- CPUs are interconnected by a shared system interconnect, allowing all CPUs to share one physical address space.
Chapter 1: Computer Organization
- A typical PC system includes components like the CPU, memory, disk controllers, USB controllers, and graphics adapters, connected by a system bus.
- Input/Output (I/O) involves CPU and device controllers accessing shared memory through the common bus, each controller associated with a specific device type.
- Interrupts alert the CPU to events needing immediate attention.
- Interrupts can happen due to either hardware or software.
Chapter 1: Storage
- Main memory is the only storage medium that the CPU accesses directly; it is volatile (data is lost when power is off).
- Secondary storage, such as hard disk drives (HDDs) and solid-state drives (SSDs), provide persistent storage.
- NVM (Non-Volatile Memory) devices like Flash Memory and SSD provide faster storage than HDD.
Chapter 1: Storage (Cont.)
- A storage hierarchy exists; from the fastest access time (registers) to slowest (magnetic tapes) with increasing storage capacity.
Chapter 2: Operating System Structures
- The operating system provides services like user interface, system calls, for executing a program, handling I/O operations (including files and devices), communicating between processes on different computers or on the same computer or over a network, allocating computer resources, and managing security and protection.
Chapter 2: User Interface (CLI)
- Command-Line Interface (CLI), a.k.a. command interpreter, allows direct command entry. CLIs fetch user commands and execute them. Built-in commands are part of the CLI, while external commands correspond to independent programs.
Chapter 2: User Interface (GUI)
- Many operating systems use Graphical User Interfaces (GUIs), with Microsoft Windows and Apple macOS being prominent examples. Unix-like systems also support GUIs like CDE, KDE, and GNOME.
Chapter 2: System Calls
- System calls act as an interface between the OS and applications, providing access to kernel services. System calls are implemented as functions in languages like C and C++. Some low-level tasks may require assembly language instructions.
Chapter 2: System Calls (Cont.)
- APIs (Application Programming Interfaces) provide developers with higher-level interfaces to the OS services. Important examples include the Win32 API, POSIX API, and the Java API.
Chapter 2: Compiler, Linker, and Loader
- Compilers translate high-level source code into low-level object code.
- Linkers combine multiple object files into a final executable.
- Loaders are responsible for bringing executable files to memory for execution.
- Static and dynamic linking of libraries differs; dynamic linking happens at run-time instead of compile time. Dynamic linking is an advantage because it keeps the size of executables small and avoids redundant loading of libraries.
Chapter 3: Processes
- A process is a program in execution. Early computer systems ran one program at a time, while modern systems can run multiple programs concurrently.
Chapter 3: Processes (Cont.)
- A process includes a text section (executable code), a data section (global variables), a heap section (dynamically allocated memory), and a stack section (temporary data).
Chapter 3: Processes (Cont.)
- The stack and heap sections can change size dynamically during program execution. Parameters, return addresses, and local variables are stored on the stack. The heap grows for dynamically allocated memory and shrinks as that memory is freed.
Chapter 3: Processes (Cont.) - Process States
- A process transitions through states: new (creation), ready (waiting to execute), running (in execution), waiting (blocked, waiting on an event), and terminated (finished).
Chapter 3: Processes (Cont.) - Process Control Block
- A process control block (PCB) is a data structure in the operating system that stores information to manage process scheduling.
Chapter 3: Processes (Cont.) - Threads
- A thread is a basic unit of CPU utilization within a single process; many processes can support multiple threads; the same process’s memory and resources are shared among the threads by default.
Chapter 3: Process Scheduling - Scheduling Queues
- The operating system uses queues (e.g., ready queue and wait queue) to manage processes awaiting execution or waiting for an event. The ready queue stores processes ready to run.
- The wait queue stores processes waiting for a particular event (like I/O).
Chapter 3: Process Scheduling - CPU Scheduling
- The CPU scheduler chooses a process from the ready queue—it is crucial to quickly switch between processes to enable responsiveness and avoid delays.
Chapter 3: Process Scheduling - Context Switch
- A context switch involves saving the state of a running process and loading the state of the next process selected by the CPU scheduler.
Chapter 3: Operations on Processes - Process Creation
- A parent process creates a child process, and the child may then create further processes. processes have IDs.
- In some cases, a new child process will inherit the parent's memory space;
- In other cases, it will execute a new program.
- When a process terminates, the parent process typically uses the
wait()system call.
Chapter 3: Operations on Processes - Process Termination
A process terminates when it finishes its defined instructions or uses the exit() system call, returning an exit status.
Chapter 7: Synchronization Examples: The Bounded-Buffer Problem
- A bounded buffer is a finite-sized buffer that is frequently used to illustrate synchronization issues in concurrent settings.
- Processes—a producer that adds items and a consumer that removes items—use a shared buffer, requiring synchronization techniques to ensure data integrity.
- Semaphores are used for this purpose.
Chapter 7: Synchronization Examples: The Dining Philosophers Problem
- Philosophers seated at a circular table, each needing both chopsticks to eat.
- The problem illustrates the deadlock possibility if processes simultaneously acquire resources needed for completion.
- Several solutions are available to solve this problem (e.g. allowing maximum four philosophers to sit, using an asymmetric approach whereby odd-numbered philosophers pick the left chopstick first and then the right and reverse for even-numbered philosophers).
Chapter 8: Deadlocks - System Model
- A deadlock occurs when each process in a set of processes is waiting for an event that can be caused only by another process in the set.
Chapter 8: Deadlock Characterization
- Deadlocks can be characterized based on four necessary conditions:
- Mutual Exclusion: Only one process can use a resource at a time.
- Hold and Wait: At least one resource is being held, and a process is waiting for another resource that is held by another process.
- No Preemption: A resource cannot be taken away from a process before it is voluntarily released.
- Circular Wait: Processes are waiting in a circular fashion, where each process is waiting for a resource held by another process that's waiting for a resource held by the original first process.
Chapter 8: Deadlock Characterization - Resource Allocation Graph
- The resource allocation graph is used to model and analyze deadlocks. Vertices consist of sets of active processes or resource types and edges represent either a request or an assignment.
Chapter 8: Deadlock Prevention
- Deadlock prevention involves preventing at least one of the four deadlock conditions:
- Mutual Exclusion: This is rarely avoidable as some resources are not sharable (e.g., printers).
- Hold and Wait: Ensuring that a process does not hold one resource while at the same time waiting for others. All the resources required by a process before starting are often the best way to manage this condition.
- No Preemption: This can be avoided by letting the OS preempt resources from a process.
- Circular Wait: To avoid this, you need to define a total ordering of resource types, ensuring that a resource is always requested in increasing order. (e.g., A process that starts by requesting processor R1 cannot later request R2, but can request R3 and then R4).
- These tactics limit how resources can be requested, potentially reducing resource utilization.
Chapter 8: Deadlock Avoidance
- Deadlock avoidance involves dynamically checking the resource allocation state to guarantee a future safe state.
- A system is in a safe state if a sequence of processes exists in which each process is able to be allocated enough required resources from those currently available to finish its execution.
Chapter 8: Deadlock Avoidance Algorithms
- Deadlock avoidance algorithms dynamically determine whether a new process can be safely granted required resources and if the system would be able to enter an unsafe state.
Chapter 8: Deadlock Detection
- Deadlock detection algorithms periodically check the system for any cyclic dependencies—meaning a deadlock situation—in the graph of resource requests.
Chapter 8: Deadlock Recovery
- Deadlock recovery strategies include:
- Abort all deadlocked processes to break up the circular relationships;
- Preempt some resources from the deadlocked processes and allocate them to other processes.
Chapter 9: Main Memory - Background
- Primary memory is where programs are loaded to execute.
- Processes must be in contiguous locations.
- The OS should manage memory to prevent processes from accessing each other's memory spaces.
Chapter 9: Main Memory - Contiguous Memory Allocation
- An early memory allocation technique that places each process in a contiguous block of memory, either in low or high memory depending on the OS.
- This approach, however, suffers from external fragmentation.
Chapter 9: Dynamic Storage Allocation
- Various algorithms—first-fit, best-fit, and worst-fit—deal with allocating suitable memory holes to processes.
Chapter 9: Paging
- A paging scheme avoids external fragmentation by breaking logical memory into fixed-size pages and physical memory into fixed-sized frames.
Chapter 9: Paging - Address Translation
- Mapping logical addresses to physical addresses by using a page table. Each virtual address has a page number and offset;
- The page number is used to index into the page table to get the frame number;
- The page offset is part of the resultant physical memory address.
Chapter 9: Internal Fragmentation
- A process might require more frames because of internal fragments to accommodate its size.
- Memory is only allocated in frames.
Chapter 9: Frame Table
- Frame tables track the status (free or occupied), and the process to which a frame is currently assigned, for each frame in memory.
Chapter 9: Structure of Page Table
- Large logical address spaces can result in very large page tables.
- To reduce this (large page table), a multilevel page table is a popular solution.
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Description
Test your knowledge on operating systems and C programming concepts including process states, command line arguments, and socket communication. This quiz covers fundamental concepts that are essential for understanding how processes work within an operating system and their interactions with C programs.
