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NSFC A Level Computer Science > Incorrect Answers > Flashcards

Incorrect Answers Flashcards

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1
Q

What is meant by problem recognition?

A

Identifying there is a problem to be solved and what the problem is.

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2
Q

What is a difference between a tree and a graph?

A

A graph has cycles.

A graph can be directed/undirected.

A graph can be weighted.

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3
Q

What are two advantages of visualisation?

A

Visualisations benefit humans rather than computers.

They present the information in a simpler form to understand.

They can best explain complex situations.

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4
Q

Describe how a 1D array can be set up and used to push and pop items as a stack. [4 marks]

A

The array size is defined.

A stack pointer is used to point to the top of the stack.

When an item is pushed to the stack, the pointer is incremented.

When an item is popped from the stack, the pointer is decremented.

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5
Q

Explain how a private attribute improves the integrity of data.

A

Properties can only be accessed through their methods.

So it cannot be changed accidentally.

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6
Q

How can a program be amended to make sure the items and queue still exist and are used the next time the program is run?

A

Store the items and queue to an external file.

Load the items and queue from the file when it starts.

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7
Q

Define the term ‘embedded operating system’.

A

System software which is built into the device itself.

It is stored in the device’s ROM.

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8
Q

Explain how a hash table can be used to handle collisions, referring to the example below. [4 marks]

A

Linear probing could be used. It moves through the structure one space at a time to find the next free space.

Chaining could be used. Each location points to the start of a linked list. The new item is added to the end of the linked list.

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9
Q

Describe what the effect would be of a computer having its BIOS overwritten. [2 marks]

A

The computer would not be able to boot/load the OS which would make the computer unusable.

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10
Q

What is a server?

A

A device which provides a central point of control.

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11
Q

Why is it important that the review score that the user entered is also checked server-side?

A

Client side processing can be modified and can sometimes be disabled on the browser.

To prevent malicious code such as an SQL injection.

To prevent a non-validated review being sent to the server.

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12
Q

Describe two ways in which the accumulator is used. [4 marks]

A

Temporary storage for data being processed during calculations.

It is also used as an I/O in the processor and is used as a buffer.

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13
Q

What happens to the PC when there is a ‘jump’ instruction?

A

The address in the CIR is sent to the PC.

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14
Q

Describe the role of the control unit in the processor. [2 marks]

A

Decodes instructions.

Sends control signals to coordinate the movement of data through the processor.

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15
Q

Describe one issue that the line ‘BRP start’ may cause for a CPU using pipelining. [2 marks]

A

BRP could be followed by one of two possible instructions, which one will only be determined at execution.

This means that the wrong instruction may be fetched and decoded.

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16
Q

What does pre-emptive mean?

A

Processes currently running can be suspended if a higher-priority item enters the queue.

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17
Q

Explain why memory management is necessary. [3 marks]

A

Organises the use of main memory by converting logical addresses to physical addresses.

It allows programs to share memory and protect data from each other.

It also allows programs larger than main memory to run.

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18
Q

State two similarities between paging and segmentation. [2 marks]

A

Both ways of partitioning memory.

Both use virtual memory to swap parts of programs.

Both allow programs larger than memory to run.

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19
Q

Explain why the first-come, first-served scheduling algorithm may not be efficient. [2 marks]

A

Once a job starts being processed, it stops other jobs from being processed.

A job using a slow resource (eg. a printer) wastes processor time.

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20
Q

Explain why a linker would need to be used after compilation. [3 marks]

A

The user running the program will not necessarily have the library installed on their machine. Therefore the relevant code needs to be included within this final executable. It is the job of the linker to provide this.

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21
Q

Describe what happens during syntax analysis when code is compiled. [5 marks]

A

The tokens are checked against the rules of the programming language.

The errors are reported as a list. Detail such as data type and scope is added to the symbol table.

It then passes the code to code generation.

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22
Q

What is the purpose of a linker?

A

Incorporates the code from the library with the main program into a single executable file.

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23
Q

Give one disadvantage to the architects’ firm of a client-server set up rather than a peer to peer setup. [1 mark]

A

Central point of failure.

Can be expensive to maintain and set up.

24
Q

The LAN is connected to the Internet via a firewall. Describe the term ‘firewall’. [1 mark]

A

A hardware device or piece of software that monitors and filters packets going <b> to and from </b> a network.

25
Q

Describe what is meant by the term ‘linked list’ [3 marks]

A

A dynamic data structure where each node consists of data and a pointer. The pointer gives the location of the next node.

26
Q

Explain why a hash table is better suited than a linked list to store the customer records, particularly as the company acquires more customers. [4 marks]

A

A linked list requires every node to be checked which will take longer to search as more customers are added. It has a time complexity of O(n).

A hash table enables direct access to the location of the record. Therefore, it will take the same amount of time to search as more nodes are added. It has a time complexity of O(1).

27
Q

Explain what the line ‘ten DAT 10’ does. [3 marks]

A

Stores the value 10 in a memory location. This memory location is given the label ten.

28
Q

Describe what is meant by the term ‘hash’. [1 mark]

A

A result generated by applying an algorithm to a value.

29
Q

Write the CSS that causes ‘text between h1 tags to be in the font Arial’. [2 marks]

A

h1
{
font-family: Arial;
}

30
Q

Give one disadvantage of this code being run client side rather than server side. [1 mark]

A

Won’t work if JavaScript is disabled.

Shows incorrect message if the computer’s clock is wrong.

Source code is visible which allows it to be copied/modified.

31
Q

Describe the Rapid Application Development process. [4 marks]

A

Prototype is created.

Feedback used to inform next iteration.

Any changes are made.

The process is repeated until the prototype becomes final product.

32
Q

What is the syntax to link to an external CSS file?

A 
rel = "stylesheet"
type = "text/css"
href = "MyCSS.css"

Inside a link tag.

33
Q

Describe why two’s complement may be preferable to sign and magnitude. [2 marks]

A

It is not easily possible to carry out calculations using sign and magnitude whereas they will work with two’s complement.

34
Q

Describe what happens during the ‘Fetch’ stage of the FDE cycle.

You should refer to the use of specific registers in your answer. [4 marks]

A

1) Address is copied from PC to MAR.
2) PC is incremented by 1.
3) Data in MAR is passed onto the address bus.
4) Read signal is sent onto the control bus.
5) RAM copies the data from the location specified by the address bus onto the data bus.
6) Data on the data bus is passed into the MDR.
7) Data is copied from the MDR to the CIR.

35
Q

Explain how pipelining would help a CPU execute the code in Fig 3.1 more quickly. [3 marks]

A

Pipelining would allow one instruction to be fetched as the previous one is being decoded and the one before that is being executed. For example, OUT could be fetched when ADD#4 is being decoded and LDA &7 is being executed.

As there are no branch instructions, it pipelines well.

36
Q

Apart from instructions being executed in a linear sequence, give three other features of Von Neumann Architecture. [3 marks]

A

Single control unit.

One instruction at a time.

Uses fetch execute cycle.

Program and data stored together.

37
Q

Describe what is meant by array processor architecture. [2 marks]

A

Single instruction, multiple data (SIMD) which allows the same instruction to operate simultaneously on multiple data locations.

38
Q

Give one advantage and one disadvantage of using Von Neumann compared with array processor architectures. [2 marks]

A

Simpler operating system.

Slower than array processing on large sets of data.

39
Q

Describe the differences between CISC and RISC. [4 marks]

A

CISC is more complex than RISC.

RISC requires more RAM than CISC.

CISC has more addressing modes.

RISC takes one machine cycle per instruction whereas CISC takes many.

40
Q

Explain the purpose of scheduling. [3 marks]

A

To make the most efficient use of the processor.

Be fair to all users and provide a reasonable response time.

Prevent processor starvation.

41
Q

Explain why the programmer could use intermediate code for the final product. [3 marks]

A

Can be used in a virtual machine.

Portable.

Protects the source code from being copied.

42
Q

What does BRP mean?

A

Branch if <b> zero or positive</b>.

43
Q

Explain what is meant by the term ‘TCP/IP stack’. [3 marks]

A

Stands for Transmission Control Protocol / Internet Protocol.

It is a protocol(s) for communicating across a network and the internet.

Each protocol belongs to a different layer.

The layers are: application, transport, internet, link.

44
Q

Explain what is meant by the character set of a computer. [2 marks]

A

Normally equates to the symbols on a keyboard that can be represented by a computer.

May include control characters.

45
Q

Give two advantages of client-server compared to peer-to-peer. [2 marks]

A

Only one point of failure.

Easier to back up.

Easier to manage users.

46
Q

Explain the purpose of a network switch. [3 marks]

A

Joins computers together on a LAN.

It receives and sends data packets.

Uses MAC addresses to send to the correct device.

47
Q

What is a foreign key? [1 mark]

A

A field that links to a primary key in a second table.

48
Q

Describe two different ways that hashing could be used in this database [4 marks]

A

For security. The passwords could be hashed to make sure they cannot be read if they are stolen.

For direct access. Records can be quickly accessed by using a hash of the index as the address.

49
Q

Explain what is meant by ‘referential integrity’ and how this could potentially be broken. [2 marks]

A

Referential integrity is where changes to databases are consistent. It can be broken if a primary key is deleted/updated. If a record is removed, all references to it must be removed.

50
Q

State the purpose of a D-type flip flop. [2 marks]

A

Stores a value of 1 bit when a signal is given.

51
Q

Describe the inputs and outputs used by a D-type flip flop circuit, explaining how the inputs are used to control the outputs. [4 marks]

A

There is a data input and a clock input and an output of Q. When the clock input goes high, Q changes to D.

52
Q

Describe one disadvantage of the use of library files to programmers [2 marks]

A

May increase the size of compiled file as the library contains many routines that aren’t being used.

Not written by the programmer so the programmer needs to spend time familiarising themselves with it.

53
Q

Explain one benefit of memory management to the user. [2 marks]

A

Security - does not let programs access memory reserved for other programs.

Multitasking - allows multiple programs to run at once.

54
Q

Define the term ‘utility’. [2 marks]

A

A piece of system software that has a single purpose used for the upkeep of the system.

55
Q

State how an application differs from a utility. [1 mark]

A

Applications perform tasks for the user rather than the computer.

Performs generic rather than specific tasks.

56
Q

Explain why the programmers of anti-virus software may make use of virtual machines when developing the updates. [3 marks]

A

Allows them to run on multiple OSs without needing multiple physical machines.

They can put viruses on the virtual machine to test if the update can catch them but protect the physical machine from the virus.

57
Q

Explain why first-come, first served would not be suitable for testing anti-virus software. [2 marks]

A

FCFS means that jobs are processed in the order they arrive in which means the virus may run first.

NSFC A Level Computer Science (26 decks)

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