1.2 Software and software development

Question 1

What is an Operating System?

Answer 1

Software that manages hardware and provides a platform for applications; manages memory, processes, security, files, I/O.

Question 2

What is paging?

Answer 2

Dividing memory into fixed-size pages; programs are divided into pages; stored in frames.

Question 3

What is segmentation?

Answer 3

Dividing memory into variable-sized segments based on logical divisions (e.g., data segment, code segment).

Question 4

What is virtual memory?

Answer 4

Using secondary storage (HDD/SSD) as an extension of RAM when physical RAM is full.

Question 5

What is an interrupt?

Answer 5

A signal sent to the processor indicating an event requiring immediate attention.

Question 6

What is an Interrupt Service Routine (ISR)?

Answer 6

A subroutine executed in response to an interrupt.

Question 7

What is a maskable interrupt?

Answer 7

An interrupt that can be ignored or delayed by the CPU.

Question 8

What is a non-maskable interrupt (NMI)?

Answer 8

An interrupt that cannot be ignored; used for critical errors (e.g., power failure).

Question 9

Round Robin scheduling.

Answer 9

Each process gets a fixed time slice (quantum); cycles through processes.

Question 10

First Come First Served (FCFS).

Answer 10

Processes executed in the order they arrive; non-preemptive.

Question 11

Multi-level feedback queue.

Answer 11

Processes move between priority queues based on behaviour; prevents starvation.

Question 12

Shortest Job First (SJF).

Answer 12

Executes the process with the smallest total execution time next; non-preemptive.

Question 13

Shortest Remaining Time (SRT).

Answer 13

Preemptive version of SJF; executes the process with the least time remaining.

Question 14

Which scheduling algorithms are preemptive?

Answer 14

Round Robin, Shortest Remaining Time (SRT).

Question 15

Which scheduling algorithms are non-preemptive?

Answer 15

First Come First Served (FCFS), Shortest Job First (SJF).

Question 16

What is a Real Time Operating System (RTOS)?

Answer 16

Guarantees response within a strict deadline; used in medical devices, airbags.

Question 17

What is a distributed OS?

Answer 17

Manages a group of independent computers and makes them appear as a single system.

Question 18

What is an embedded OS?

Answer 18

Designed for specific devices with limited resources (e.g., smartwatch, microwave).

Question 19

What is a multi-tasking OS?

Answer 19

Allows multiple tasks/processes to run concurrently by sharing CPU time.

Question 20

What is a multi-user OS?

Answer 20

Allows multiple users to access the system simultaneously.

Question 21

What is BIOS?

Answer 21

Basic Input Output System; firmware stored in ROM; initialises hardware and boots the OS.

Question 22

What does POST stand for?

Answer 22

Power On Self Test.

Question 23

What does POST do?

Answer 23

Checks that essential hardware (RAM, keyboard, storage) is present and functioning before booting.

Question 24

What is a device driver?

Answer 24

Software that allows the OS to communicate with a specific hardware device.

Question 25

What is a **virtual machine**?

Answer 25

A software emulation of a physical computer; runs an OS within another OS (e.g., VirtualBox, JVM).

Question 26

What are **utilities**?

Answer 26

System software that performs maintenance tasks (e.g., defragmentation, backup, antivirus).

Question 27

**Open source** vs **Closed source**.

Answer 27

Open: Source code available, often free, community modified (e.g., Linux). Closed: Source code hidden, owned by company (e.g., Windows).

Question 28

What does an **interpreter** do?

Answer 28

Translates and executes source code line-by-line; slower; easier debugging.

Question 29

What does a **compiler** do?

Answer 29

Translates entire source code into machine code in one go; produces an executable; faster execution.

Question 30

What does an **assembler** do?

Answer 30

Translates assembly language (mnemonics) into machine code.

Question 31

**Lexical analysis** stage.

Answer 31

Removes comments/whitespace; replaces constants with tokens; builds symbol table.

Question 32

**Syntax analysis** stage.

Answer 32

Checks token sequence against grammar rules; builds Abstract Syntax Tree (AST).

Question 33

**Code generation** stage.

Answer 33

Converts AST into object/machine code.

Question 34

**Code optimisation** stage.

Answer 34

Makes code more efficient (faster/less memory) without changing functionality.

Question 35

What is a **linker**?

Answer 35

Combines multiple object code files and libraries into a single executable.

Question 36

What is a **loader**?

Answer 36

Loads the executable into memory and starts it.

Question 37

**Waterfall** model.

Answer 37

Sequential stages (Analysis -> Design -> Code -> Test -> Maintain); rigid; good for safety critical systems.

Question 38

**Agile** methodologies.

Answer 38

Iterative; incremental; flexible requirements; frequent customer feedback (e.g., Scrum, XP).

Question 39

**Spiral** model.

Answer 39

Risk driven; combines iterative with waterfall; suitable for large, high-risk projects.

Question 40

**Rapid Application Development (RAD)**.

Answer 40

Prototyping over planning; fast delivery; user involvement; timeboxed.

Question 41

**Extreme Programming (XP)**.

Answer 41

Agile methodology; pair programming, test-driven development, continuous integration.

Question 42

When would you use **Waterfall**?

Answer 42

Requirements are fixed and clear; safety critical systems; low client involvement needed.

Question 43

When would you use **Agile**?

Answer 43

Requirements likely to change; client available for feedback; fast delivery needed.

Question 44

**Immediate addressing**.

Answer 44

Operand is the actual value (e.g., `LDA #5`).

Question 45

**Direct addressing**.

Answer 45

Operand is the memory address where the value is stored (e.g., `LDA 50`).

Question 46

**Indirect addressing**.

Answer 46

Operand points to a memory location that contains the address of the data.

Question 47

**Indexed addressing**.

Answer 47

Adds an index register to the address to calculate effective address (useful for arrays).

Question 48

**LMC Mnemonic: ADD**

Answer 48

ADD - Add.

Question 49

**LMC Mnemonic: SUB**

Answer 49

SUB - Subtract.

Question 50

**LMC Mnemonic: STA**

Answer 50

STA - Store (Alternative: STO).

Question 51

**LMC Mnemonic: LDA**

Answer 51

LDA - Load (Alternative: LOAD).

Question 52

**LMC Mnemonic: BRA**

Answer 52

BRA - Branch always (Alternative: BR).

Question 53

**LMC Mnemonic: BRZ**

Answer 53

BRZ - Branch if zero (Alternative: BZ).

Question 54

**LMC Mnemonic: BRP**

Answer 54

BRP - Branch if positive (Alternative: BP).

Question 55

**LMC Mnemonic: INP**

Answer 55

INP - Input (Alternatives: IN, INPUT).

Question 56

**LMC Mnemonic: OUT**

Answer 56

OUT - Output.

Question 57

**LMC Mnemonic: HLT**

Answer 57

HLT - End program (Alternatives: COB, END).

Question 58

**LMC Mnemonic: DAT**

Answer 58

DAT - Data location (reserves memory).

Question 59

What is a **class**?

Answer 59

A blueprint/template for creating objects.

Question 60

What is an **object**?

Answer 60

An instance of a class.

Question 61

What is **encapsulation**?

Answer 61

Bundling data (attributes) and methods (procedures) that operate on the data; restricting direct access (private).

Question 62

What is **inheritance**?

Answer 62

Creating a new class (child) based on an existing class (parent); inherits attributes/methods.

Question 63

What is **polymorphism**?

Answer 63

Ability to present the same interface for different underlying data types (e.g., method overriding).