OS Support

Question 1

7 key functions of an OS

Answer 1

1. program creation
2. program execution
3. I/O device management
4. file system control
5. system access
6. error handling
7. performance monitoring

Question 2

what is an OS

Answer 2

fundamental software that manages a computer’s hardware and software resources, allowing users to interact with their devices and applications

Question 3

what is program creation with OS

Answer 3

utilities like editors and debuggers to assist in software development

Question 4

what is program execution with OS

Answer 4

manages loading programs into memory, initialising I/O, and allocating resources

Question 5

what is I/O device management with OS

Answer 5

simplifies interactions by abstracting device-specific commands

Question 6

what is file system control with OS

Answer 6

handles file organisation, storage and access permissions

Question 7

what is system access with OS

Answer 7

protects resources from unauthorised access and manages user permissions

Question 8

what is error handling with OS

Answer 8

detects and responds to hardware/software failures to minimise system disruptions

Question 9

what is performance monitoring with OS

Answer 9

tracks resource usage and system efficiency for optimisation

Question 10

what are the 4 types of OS

Answer 10

1. early computers
2. batch OS
3. multiprogrammed batch systems
4. time-sharing systems

Question 11

describe OS in early computers

Answer 11

• no OS
• loaded using toggle switches or card readers
• manual debugging
• issues: setup & scheduling

Question 12

describe a batch OS

Answer 12

• users submit jobs
• computer operator collects multiple jobs & batches them
• monitor loads & runs jobs 1-by-1 automatically
• processor executes each job sequentially
• job control language tells monitor what program to execute

Question 13

what were the new hardware features needed in batch OS

Answer 13

1. memory protection - preventing user programs from modifying the OS
2. timer - ensuring no job monopolises the system
3. privileged instructions - certain commands can only be executed by the OS
4. interrupts - allow OS to regain control from user programs

Question 14

describe multiprogrammed batch systems

Answer 14

• allows multiple programs in memory
• when one program waits for I/O, the CPU switches to another
• ^ CPU utilisation
• no multiprogramming = idle resources
• uses I/O interrupts & DMA
• requires memory management
• needs scheduling algorithms

Question 15

describe time-sharing systems

Answer 15

• allows multiple users to interact with the system simultaneously
• OS rapidly switches between user programs, giving each as short time slice
• users experience fast response times

Question 16

difference between multiprogrammed batch systems & time-sharing systems

Answer 16

• multiprogrammed batch: CPU switches between jobs only when one is waiting for I/O
• time-sharing: CPU switches ar regular intervals to fairly share time among users

Question 17

why is scheduling needed

Answer 17

essential for efficient multiprogramming, ensuring resource utilisation

Question 18

4 types of scheduling

Answer 18

1. long-term
2. medium-term
3. short-term
4. I/O scheduling

Question 19

describe long-term scheduling

Answer 19

• decides which jobs are admitted into the system
• controls the degree of multiprogramming
• BATCH = jobs were queued and prioritised before being admitted to execution
• TIME-SHARING = OS accepts all users until the system reaches saturation
• job becomes a process and moves to the short-term scheduler’s queue

Question 20

describe medium-term scheduling

Answer 20

• helps control degree of multiprogramming by ensuring efficient memory use
• swapping-out: RAM to disk when memory is full
• swapping-In: brings processes back to RAM when memory becomes available
• important in systems without virtual memory to optimise resource use

Question 21

describe short-term scheduling

Answer 21

makes frequent decisions on which job to execute next

Question 22

what are the 5 process states during its lifetime

Answer 22

1. new: admitted but not yet ready for execution
2. ready: waiting for processor access
3. running: actively being executed
4. waiting: suspended, waiting for system resource
5. halted: process has completed execution

Question 23

what is a process control block (PCB)

Answer 23

• OS maintains a PCB for each process, storing its state & essential execution info
• new job = OS creates a blank PCB & initialises it before moving the process to the ready state

Question 24

what three queues does the OS maintain in scheduling

Answer 24

1. long-term - jobs waiting to enter the system
2. short-term - ready processes competing for CPU time
3. I/O - processes waiting for specific output devices

Question 25

how does the OS use queues & scheduling

Answer 25

- OS gains control when an interrupt or service call occurs - short term scheduler selects the next process to execute from the maintained OS queues - typically round-robin or priority-based

Question 26

describe the process flow in OS scheduling

Answer 26

- new process requests enter the long-term queue - once admitted, a process moves to the short-term queue - OS selects a process for execution& hands control over to the CPU - processes may be suspended for I/O or timeout, moving to I/O or short-term queues - OS manages I/O queues and resumes processes when their I/O completes