Operating System Overview

Flashcards covering the key vocabulary and concepts of Operating Systems from the lecture notes.

Operating System

A system software that manages all the resources of the computer and acts as an intermediary between an end user and the computer hardware.

GUI

Graphical User Interface, providing elements like windows, icons, menus, and toolbars for user interaction.

Efficiency (in OS)

Allows computer system resources to be used in an efficient manner.

Convenience (in OS)

Makes the computer more convenient to use.

Interface

An intermediary that facilitates interaction between application programs and hardware.

Program execution

The process where the OS prepares resources needed for executing a program.

I/O devices

Input/Output devices that the operating system manages for ease of use by programmers.

File management

The OS helps to create, delete, read, and write files while controlling access.

System access

Controls access to the system and specific resources to protect data from unauthorized access.

Error detection

The OS is responsible for detecting and handling errors that can arise from hardware or software.

Uniprogramming

A method where only a single program executes at a time.

Multiprogramming

Allows multiple programs to reside in main memory and execute concurrently.

Kernel

The core component of the operating system that performs essential OS services.

Shell

An interface that acts as a connection between the user and the operating system.

User Mode

The mode in which user applications run and do not have direct access to hardware.

Kernel Mode

The mode where the operating system has full access to hardware and system resources.

System Call

An interface between user applications and the operating system that allows requests for services.

Process

An instance of a program in execution.

Process Control Block (PCB)

A data structure containing important information about a process, created and managed by the OS.

Process States

The different states a process can be in: new, ready, running, blocked, terminated.

Context Switch

The process of saving the state of a currently running process and loading the state of another process.

Dispatcher

A program that switches the processor from one process to another, handling task distributions.

CPU bound process

A process that spends more time performing computations than waiting for I/O operations.

I/O bound process

A process that spends more time waiting for I/O operations than performing computations.

Process Creation

The OS creates processes and manages their resources when executing user programs.

Process Termination

The event where an active process ends its execution and frees its allocated resources.

Process Scheduling

The method used by the OS to determine the execution order of processes.

Job Queue

A queue that contains all processes in the system.

Ready Queue

A queue of processes residing in memory that are ready to execute.

Long-term Scheduler

Also known as the job scheduler, it selects processes from the job queue to run.

Short-term Scheduler

Also known as the CPU scheduler, it selects processes from the ready queue for execution.

Throughput

The number of processes that complete their execution in a unit of time.

Turnaround time

The total time taken from process submission to its completion.

Waiting time

The amount of time a process has been waiting in the ready queue.

First-Come, First-Served (FCFS)

A non-preemptive scheduling algorithm where the first process to arrive gets executed first.

Shortest Job First (SJF) Scheduling

A scheduling algorithm that prioritizes processes with the shortest execution time.

Priority Scheduling

Allocates CPU to processes based on the priority assigned to each process.

Round Robin Scheduling (RR)

A preemptive scheduling algorithm assigning a fixed time slice to each process.

Multilevel Queue Scheduling

A scheduling method where different queues exist for different types of processes.

Semaphore

A synchronization tool used to manage access to shared resources and prevent race conditions.

Deadlock

A situation where two or more processes are waiting indefinitely for each other to release resources.

Mutual Exclusion (in deadlock prevention)

Only one process can use a resource at a time, preventing deadlock.

Hold and Wait (in deadlock conditions)

A process holding at least one resource while waiting for additional resources, allows potential deadlocks.

No Preemption (in deadlock conditions)

Resources allocated to a process cannot be forcibly taken away.

Circular Wait (in deadlock conditions)

A situation where a closed chain of processes exists where each process holds a resource that the next in the chain needs.

Deadlock Prevention

Techniques designed to ensure that at least one condition necessary for deadlock cannot occur.

Deadlock Avoidance

Dynamically deciding whether resource allocation might lead to a deadlock.

Banker’s Algorithm

An algorithm used to avoid deadlocks by checking the state of resource allocation.

Fragmentation

Unused memory space that occurs when processes are loaded and removed from memory.

Internal Fragmentation

Wasted space within an allocated memory block that cannot be utilized.

External Fragmentation

Memory is divided into small scattered blocks preventing large contiguous memory allocation.

Compaction

A technique for eliminating fragmentation by moving memory blocks closer together.

Paging

A memory management scheme eliminating the need for contiguous memory allocation.

Segmentation

A memory management technique dividing processes into variable-sized segments.

Virtual Memory

Technique that allows the execution of processes that may not be completely in memory.

Demand Paging

A memory management approach where pages are only loaded into RAM when needed.

Magnetic Disk

A storage device that uses magnetic material to store information on rotating platters.

Disk Scheduling

The method used by the operating system to manage the order of disk input/output requests.

FCFS (Disk Scheduling)

A disk scheduling algorithm that processes requests in the order they arrive.

SSTF (Shortest Seek Time First)

Disk scheduling that selects the request with the minimum seek time from the current head position.

SCAN (Disk Scheduling)

Disk scheduling method that moves the disk arm in one direction servicing requests.

C-SCAN (Circular SCAN)

Disk scheduling method that services requests in one direction and returns to the start without servicing on the return trip.

C-LOOK (Circular LOOK)

A variation of C-SCAN that only services requests as far as the last request in each direction.

Head Movement (in scheduling)

Distance the disk head must move to fulfill I/O requests.

Pros and Cons of Scheduling Algorithms

Each disk scheduling algorithm has unique advantages and disadvantages based on wait times, efficiency, and fairness.

Performance characteristics of mass-storage devices

Factors influencing how efficiently a storage device operates, including speed, capacity, and reliability.

Physical structure of secondary storage devices

The layout and components that make up devices like hard disks and SSDs.

Access time (Disk Characteristics)

The total time taken to access data from a storage device, including seek time and latency.

Seek time (Disk Characteristics)

The time it takes for the read/write head to move to the track of interest.

Rotational Latency (Disk Characteristics)

The delay waiting for the desired sector to rotate into position under the read/write head.

Head Crash (Disk Characteristics)

Damage caused when the read/write head comes into contact with the disk surface.

Secondary Storage Systems

Additional storage devices like hard drives, SSDs, and tapes used for data that does not require fast access.