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Questions and Answers
What is the purpose of a Process Control Block (PCB)?
Which component of the PCB helps determine which instruction a process should execute next?
In the context of a PCB, what does CPU Scheduling information include?
What triggers the creation of a new process according to the text?
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Which type of process is associated with specific functions rather than user interaction?
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What does the Process ID (PID) represent in the context of process management?
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In a multiprogramming environment, processes never compete for resources.
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If a process requests a resource that is not available, it immediately exits the system.
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A deadlock situation can only occur if the Request condition is met.
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In a deadlock, at least one resource must be held in a shareable mode.
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Circular wait is one of the necessary conditions for a deadlock to occur.
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A process can use a resource without requesting it first.
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Under normal operation, a process may utilize resources in any arbitrary sequence.
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Round-Robin Algorithm guarantees the shortest average waiting time for processes.
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Multilevel Queue Scheduling assigns each process to a single queue.
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CPU bursts are continuous and do not have any idle time during execution.
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Study Notes
Job and Processes
- A job is a set of program instructions corresponding to a particular computational task, such as payroll or inventory.
- In multiprocessor systems, a job is a group of collaborating processes forming a unit.
- The terminology "job" developed during the time when the major activity of the Operating System (OS) was job processing.
- Jobs are typically executed without user input for minutes, hours, or days.
- The term "job" is often used interchangeably with "process".
Processes
- A process is a program in execution, requiring certain resources such as CPU time, memory, files, and I/O devices to accomplish its task.
- A process is an asynchronous activity and is referred to as the "animated spirit" of a procedure.
- A process moves through a series of discrete states, including:
- Newborn: process creation
- Running: process is executing instructions
- Waiting: process is waiting for I/O or event completion
- Ready: process is waiting for CPU
- Terminated: process has finished execution
- A process has an address space consisting of:
- Text region: stores the code that the processor executes
- Data region: stores variables and dynamically allocated memory
- Stack region: stores instructions and local variables for active procedure calls
Process Control Block (PCB)
- A Process Control Block (PCB) is a data structure that maintains information about a process.
- A PCB is created by the OS and includes information such as:
- Process ID (PID)
- Process state (running, ready, or waiting)
- Program counter
- Credentials
- Pointer to the process's parent process
- CPU scheduling information
- Pointers to the process's child processes
- Memory-management information
- I/O status information
Resource Allocation
- Resources vary from system to system, but a typical OS has to allocate the following items to a process:
- CPU
- Memory
- Registers
- I/O devices
- Files
- Scheduling queues include:
- Job queue: processes that enter the system are put in this queue
- Ready queue: keeps all processes that are residing in main memory and are ready and waiting to execute
- Device queues: keep all processes waiting for a particular I/O device
Schedulers
- Long-term scheduler (job scheduler): selects a process from a pool of processes and loads it into memory for execution.
- Short-term scheduler (CPU scheduler): selects from among the processes that are ready to execute and allocates the CPU to one of them.
- Medium-term scheduler: an additional level of scheduling that supports the idea of swapping processes in and out of memory.
CPU Scheduling
- CPU scheduling is the basis of multiprogrammed OS.
- CPU scheduling is a fundamental OS function that allows the OS to make the computer system more productive.
Scheduling Policies
- Scheduling policies include:
- First-Come-First-Served (FCFS): allocates the CPU to the process that requests the CPU first.
- Shortest-Job-First (SJF): allocates the CPU to the process with the shortest next CPU burst.
- Priority Scheduling: allocates the CPU to the process with the highest priority.
- Round-Robin (RR) Algorithm: designed especially for time-sharing systems, uses a small unit of time called a quantum or time slice.
- Multilevel Queue Scheduling: partitions the ready queue into several separate queues, each with its own scheduling algorithm.
- Multilevel Feedback Queue Scheduling: allows a process to move between queues.
Algorithm Evaluation
- Algorithm evaluation methods include:
- Analytic evaluation: uses the given algorithm and the system workload to produce a formula or number that evaluates the performance of the algorithm for that workload.
- Deterministic modeling: uses a particular workload and defines the performance of each algorithm for the workload.### Process Management
- Process Management deals with the allocation and management of system resources
- Process Control Block (PCB) is a data structure that contains information about a process
- Process Termination occurs due to:
- Normal exit (voluntary)
- Error exits (voluntary)
- Fatal error (involuntary)
- Killed by another process (involuntary)
Resource Allocation
- Resources vary from system to system, but a typical OS has to allocate:
- CPU
- Memory
- Registers
- I/O devices
- Files
- Resource Allocation involves:
- Long-term scheduling (job scheduling)
- Short-term scheduling (CPU scheduling)
- Job queue: processes that enter the system are put in this queue
- Ready queue: keeps all processes that are residing in main memory and are ready to execute
- Device queues: keep all processes waiting for a particular I/O device
Scheduling
- Scheduling involves selecting a process from the ready queue and allocating the CPU to that process
- Schedulers:
- Long-term scheduler (job scheduler): selects a process from a pool of processes and loads it into memory for execution
- Short-term scheduler (CPU scheduler): selects from among the processes that are ready to execute and allocates the CPU to one of them
- Medium-term scheduler (optional): supports the idea of adding and removing processes from main memory
- Context Switch: the task of switching the CPU to another process, which requires saving the state of the old process and loading the saved state for the new process
Scheduling Policies
- Scheduling policies include:
- First-Come, First-Served (FCFS)
- Shortest-Job-First (SJF)
- Priority Scheduling
- Round-Robin Algorithm (RR)
- Multilevel Queue Scheduling
- Multilevel Feedback Queue Scheduling
- Each policy has its own criteria, such as:
- CPU utilization
- Throughput
- Turnaround time
- Response time
- Waiting time
- Priority
Algorithm Evaluation
- Algorithm evaluation involves:
- Analytic evaluation: uses a formula or number to evaluate the performance of an algorithm for a given workload
- Deterministic modeling: evaluates the performance of an algorithm for a given workload
- Evaluation methods include:
- FCFS
- SJF
- RR (quantum = 10)
Deadlocks
- Deadlocks occur when:
- A process requests a resource that is not available
- The process waits for the resource to become available
- The waiting process holds resources that are requested by other waiting processes
- Necessary conditions for a deadlock to occur:
- Mutual exclusion: at least one resource must be held in a non-sharable mode
- Hold and wait: a process must be holding one resource and waiting for another resource
- No preemption: a process cannot be forced to release a resource
- Circular wait: a set of waiting processes must exist, each waiting for a resource held by the next process in the set
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Description
Test your knowledge on multiprogramming, process management, resource allocation, scheduling policies, and deadlock in operating systems. This quiz covers topics like jobs, processes, and the collaboration among them in a multiprocessor system.
