Computers

Question 1

What is a

computer?

Answer 1

a machine that takes some kind of input from its surroundings and then processes it to produce an output

Question 2

What are

hardware?

Answer 2

the physical components of a computer system

Question 3

What is

software?

Answer 3

the set of programs running on the hardware which direct the computer to perform specific operations

Question 4

What is the

stored program concept?

Answer 4

a proposed design for a new computer architecture where both program instructions and data are stored together in a computer’s main memory

this was by von Neumann

this is based on the premise that program instructions are only stored in a computer’s memory for as long as they are needed

Question 5

What does the

von Neumann architecture consist of?

Answer 5

main memory and a central processing unit interconnected by buses

Question 6

What does

main memory consist of?

Answer 6

a collection of storage locations, each with their own memory address

Question 7

What does it mean to be

volatile?

Answer 7

the content is lost when the power is turned off

Question 8

What does the

CPU consist of?

(3)

Answer 8

• control unit (CU)
• arithmetic logic unit (ALU)
• registers

Question 9

What does the

control unit do?

(2)

Answer 9

• decodes instructions received from main memory
• coordinates the actions of the other parts of the CPU in order to execute them

Question 10

What does the

arithmetic logic unit do?

Answer 10

performs arithmetic and logic operations on data

Question 11

What do

registers do?

and what are some examples? (2)

Answer 11

provide fast, temporary storage for instructions, intermediate results and data

instruction register -> holds the instruction currently being executed
accumulator -> holds the results of calculations performed by the ALU

Question 12

What are the

three types of bus?

Answer 12

• address bus
• data bus
• control bus

Question 13

What does the

address bus do?

Answer 13

carries the address of the memory location that the CPU will read from or write to

(this is unidirectional)

Question 14

What does the

data bus do?

Answer 14

holds the value being read from or written to memory

(this is bidirectional)

Question 15

What does the

control bus do?

Answer 15

carries the command signals from the control unit to other components so that they know whether to read or write data, and the status signals back to the CPU

(this is bidirectional)

Question 16

What is the

bus width?

Answer 16

the number of connections on a bus

a greater bus width means that a larger number of values can be communicated

Question 17

What does the

clock do?

Answer 17

sends out electronic signals at regular intervals to all the other hardware components in order to synchronise their actions

Question 18

What does

clock speed affect?

Answer 18

the faster the clock, the more instructions the CPU can execute per second

Question 19

What is

pipelining?

Answer 19

the process of modern CPUs that execute programs more quickly by overlapping the stages of the fetch-execute cycle

Question 20

What are the differences between

main memory and secondary storage?

(4)

Answer 20

secondary storage:
- non-volatile
- slower
- cheaper
- higher capacity

Question 21

What are the

three common physical ways of recording binary data?

Answer 21

• magnetic storage (hard drives)
• optical storage (CDs and DVDs)
• solid-state storage - aka ‘flash’ memory (USB memory sticks and SD cards)

Question 22

What is inside a

hard disk drive?

(magnetic secondary storage)

Answer 22

A stack of disks called platters made from a hard material (e.g. glass or ceramic).
The surface of each platter has a thin magnetic coating and is divided into billions of tiny areas.

Question 23

How is data stored in a

hard disk drive?

(magnetic storage)

Answer 23

Data is stored on the surface of a platter as a series of bits. An area that is magnetised represents a 1.

(and vice versa)

Question 24

How is data read/written onto a

hard disk drive?

(magnetic storage) (3 steps)

Answer 24

1. Each platter has two magnetic read-write heads.
2. These move in and out above the surface as the platter rotates at a high speed. (The arm positions the heads over the correct area of the platter to read or write data.)
3. To write data to the disk, the heads alter the magnetic state of the surface. To read data, they detect the magnetic state.

Question 25

# How is data stored on optical storage?

Answer 25

Data is written along a single track that spirals out from the centre of the disk. It is stored as a series of pits and lands on the surface of the disk. A land represents the binary value 1 and a pit the value 0.

Question 26

# How do you write data onto an optical disk?

Answer 26

The laser heats the recording material, which changes its form to become more or less reflective. Reflective areas represent lands and less reflective areas represent pits.

Question 27

# How do you read data from an optical disk?

Answer 27

A laser beam is shone onto the surface. The amount of light reflected is detected by a light sensor and then interpreted as 1s and 0s.

Question 28

# What are some positives of solid-state storage? | (4)

Answer 28

- no moving parts - energy-efficient - small - high-capacity

Question 29

# How is data stored on solid-state storage?

Answer 29

chips (called NAND flash) trap electrons in a 'pool' | full pools represent 0s, empty pools represent 1s

Question 30

# How do you write data onto a solid-state storage? | (3 steps)

Answer 30

1. Control signals identify the pool to be written. 2. They apply very precise electrical charges. 3. These cause electrons to move between two pools. ## Footnote A higher voltage pulls more electrons, which block current flow. Blocked current flow represents 0.

Question 31

# How do you read data from solid-state storage?

Answer 31

1. Control signals identify which bit is to be read. 2. They apply a small voltage. 3. If the electron pool is empty, the transistor turns on and a 1 is read out. If the electron pool is full the transistor doesn't turn on and a 0 is read out.

Question 32

# What is the key negative of solid-state storage?

Answer 32

both erasing and writing cause the transistor to break down over time | this limits the life of a flash drive

Question 33

# Define embedded system.

Answer 33

a small computer designed to perform one specific function

Question 34

# What are some characteristics of embedded systems? | (2)

Answer 34

- limited functionality - customised hardware and software

Question 35

# What components are in an embedded system? | (4)

Answer 35

- sensors - battery - microcontroller - actuators

Question 36

# What does the microcontroller in an embedded system consist of? | (4)

Answer 36

- flash memory - RAM - CPU - peripherals

Question 37

# How does an embedded system work? | (4 steps)

Answer 37

1. Input devices (e.g. sensors) supply an embedded system with information from the outside world. 2. Data received is stored temporarily in the microcontrollers RAM. 3. The CPU interprets and acts upon the data according to the program instructions stored in flash memory. 4. If necessary a signal is sent to an output device (e.g. actuators) to carry out an appropriate action.

Question 38

# What is the Internet of Things?

Answer 38

the collection and exchange of data by embedded systems with little or no human intervention

Question 39

# What are the three main types of software?

Answer 39

- operating system - application software - utility software

Question 40

# What is the operating system?

Answer 40

a program that controls and manages the hardware and all other software on a computer and provides an interface for users

Question 41

# What is application software?

Answer 41

programs or apps designed for end users | e.g. web browser, spreadsheet, console game, email client

Question 42

# What are some examples of operating systems? | (4)

Answer 42

- Microsoft Windows - Linux - Android - iOS

Question 43

# What are the key functions of an operating system? | (4)

Answer 43

1. File management 2. Process management 3. Peripheral management 4. User management

Question 44

# How are files organised by an operating system?

Answer 44

Files are organised in a hierarchical tree structure. ## Footnote The top node of the tree is the root directory. Nodes lower down are either directories, sub-directories or files. Every file in the system has a unique path so that it can be easily located.

Question 45

# What is the key benefit of a hierarchical tree structure?

Answer 45

the filename can be used more than once

Question 46

# What does the operating system do when there's a new file to be stored? | (3 steps)

Answer 46

1. It splits the file up into smaller pieces. 2. It stores each piece in an empty sector on the hard drive. 3. It keeps a record of the start location and sequence number of each piece so that it can retrieve and reassemble the file when it is required.

Question 47

# What are the four different file permissions?

Answer 47

- read - write - execute - delete

Question 48

# Define process.

Answer 48

a program that is loaded into main memory and is being executed

Question 49

# What are the three key scheduling algorithms?

Answer 49

- first in, first out - shortest job first - round robin

Question 50

# How does first in, first out work? | (2 steps)

Answer 50

1. Processes queue in the order in which they arrive. 2. The process at the head of the queue gets to use the CPU until it is finished or is help up waiting for another resource like a printer.

Question 51

# How does shortest job first work?

Answer 51

The process which is closest to finishing goes next.

Question 52

# How does round robin work? | (2 steps)

Answer 52

1. Processes wait their turn in a queue. The process at the head of the queue goes next. 2. At the end of its time slice, if it isn't finished, it goes to the back of the queue and the next process is taken from the front of the queue. ## Footnote Some processes have a higher priority than others and get more time slices.

Question 53

# What is virtual memory? | and why does this occur?

Answer 53

when a paging algorithm swaps processes out of RAM and onto the hard drive | this occurs when RAM gets full

Question 54

# Define device driver.

Answer 54

a piece of software that relays instructions and data between the OS and the peripheral device

Question 55

# What are the three different types of user interface?

Answer 55

- graphical user interface (GUI) -> windows, icons, menus and pointers - WIMP -> e.g. Microsoft Windows, macOS - command-line text interface (CLI)

Question 56

# What is utility software?

Answer 56

a collection of tools that help minimise the impact of data loss or damage caused by events such as a system failure, cyberattack, fire or flood

Question 57

# What are some examples of utility software? | (5)

Answer 57

- file repair - backup - data compression - disk defragmentation - anti-malware

Question 58

# What does a file repair tool do?

Answer 58

scans a damaged file, extracts as much data from it as possible, and stores it in a new useable file

Question 59

# What does backup do?

Answer 59

It automatically backs up data stored on a computer's hard drive to another location, such as a network drive or the cloud. ## Footnote Should a file get lost or damaged, the most recent backup can be restored.

Question 60

# What does a data compression tool do?

Answer 60

Compresses filed to reduce their file size, freeing up storage space and speeding up their transfer across networks.

Question 61

# What does a disk defragmenter do?

Answer 61

Addresses the problem caused by fragmentation on magnetic hard drives by rearranging the files so that every file is stored in sequential sectors and free space is grouped together.

Question 62

# What does anti-malware do?

Answer 62

tries to eleminate malicious software from a computer

Question 63

# Define robust software.

Answer 63

software that is capable of handling the unexpected without crashing, generating incorrect output or revealing sensitive data

Question 64

# Define code vulnerability.

Answer 64

a flaw in a program that compromises security ## Footnote this can be exploited by an attacker to - gain access to a computer system, enabling them to steal or corrupt data - introduce malware - take over control of the computer for some purpose of their own

Question 65

# What are some examples of bad programming habits? | (6)

Answer 65

- not thought-through design - not sticking to agreed coding practices and standards - making do with a temporary fix for a problem - writing unstructured code instead of separating it into subprograms - useing third party library modules without checking that they are free from vulnerabilities - skimping on testing

Question 66

# What is the purpose of code reviews? | and what are the two different types of this?

Answer 66

to spot instances of poor programming practice, find any vulnerabilities and check code efficiency | review by another programmer, automated review

Question 67

# What happens with review by another programmer? | and why is this bad?

Answer 67

A more senior reviewer will look at the code produced, checking to see if any bad programming practices have been used or if any code vulnerabilities are present. | This is labour intensive and time consuming.

Question 68

# What happens with automated review? | and why is this bad?

Answer 68

A specialist piece of software is used to examine the code. This software will highlight potential issues such as vulnerabilities or obvious bad programming practice. | This probably won't identify every issue.

Question 69

# What is an audit trail? | and why is this good?

Answer 69

a track of who made what changes and when | it reduces errors and improves accountability

Question 70

# Define instruction set.

Answer 70

the instructions that a CPU can execute

Question 71

# Define machine code.

Answer 71

the binary codes representing a program

Question 72

# Give three examples of high-level languages.

Answer 72

- python - visual basic - java

Question 73

# Give an example of a low-level language.

Answer 73

assembly language

Question 74

# Why is it harder to write programs in low-level languages? | (3)

Answer 74

- there are a very limited range of instructions - there are no strings, integers or real numbers - debugging can be more difficult

Question 75

# What are the differences between compiled and interpreted code's translation?

Answer 75

compiled -> all the code is translated prior to being executed interpreted -> each source line is translated to object code just before it is executed

Question 76

# What are the differences between compiled and interpreted code's speed?

Answer 76

compiled -> faster, more efficient, because it doesn't have to be translated as it is executing interpreted -> slower, because source code is translated line by line while execution is underway

Question 77

# What are the differences between compiled and interpreted code's error reporting?

Answer 77

compiled -> errors are reported in a batch once the compiler has finished translating the source code interpreted -> an error in the source code is reported as soon as it is encountered

Question 78

# What are the differences between compiled and interpreted code's code amendments?

Answer 78

compiled -> code must be recompiled if code is amended interpreted -> code must be translated and executed again is code if amended

Question 79

# What are the differences between compiled and interpreted code's source code availability?

Answer 79

compiled -> only an executable file is given to the user, the original source code is not visible interpreted -> the source code must be given to the user to run on their machine, so it is visible

Question 80

# What are the differences between compiled and interpreted code's portability?

Answer 80

compiled -> code is machine dependent, it will only run on a computer with a particular machine architecture - the source code would have to be recompiled in order for it to run on a computer with a different architecture interpreted -> code is platform independent and can be translated on any computer that has a suitable interpreter