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Edexcel GCSE Computer Science (1CP2) Exam Questions

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3 questions · 9 marks

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1Short recall1 markProtocols & Layers Swap Remove

TCP is a protocol in the transport layer of the TCP/IP model.

State one role of TCP when data is transmitted over a network.

[1 mark]
Mark scheme

Award one mark for any of the following up to a maximum of one mark:

  • Breaks messages/data into packets (1)
  • Reassembles packets (at the destination) (1)
  • Detects errors (1)
  • Resends lost/missing packets/requests retransmission of lost packets (1)
  • Creates/establishes a connection between two computers/hosts/sets up a connection before data is sent (1)

Do not accept routing packets or using IP addresses, which is the role of IP.

Do not accept encrypting data or providing security.

Do not accept vague answers such as 'transmits data' or 'sends data' without saying how TCP does this.

Example answers and how they were marked
Full marks1/1

It splits data into packets.

Why: States that TCP breaks data into packets.

No marks0/1

It routes packets between IP addresses.

Why: Near-miss: routing packets is the role of IP, not TCP.

No marks0/1

It encrypts data so it is secure.

Why: Encryption is not a role of TCP, so no creditworthy point.

2Describe2 marksFetch Decode Execute Cycle Swap Remove

The control unit is one component of the CPU.

Describe the role of the control unit in the fetch-decode-execute cycle.

[2 marks]
Mark scheme

Award up to two marks for a linked description such as:

  • Decodes instructions (1) to determine what action/operation is required (1)
  • Sends control signals (1) along the control bus to coordinate/control the actions of other components (1)
  • Controls the fetch stage (1) by causing the next instruction to be fetched from main memory/RAM (1)
  • Controls the execute stage (1) by telling the ALU/other components when to carry out the required operation (1)

Do not accept responses relating to how the control unit affects performance, such as increasing clock speed.

Do not accept responses that describe the role of the ALU, registers or clock instead of the control unit.

Do not accept responses about the ALU performing calculations unless the control unit controlling the ALU is also stated.

Example answers and how they were marked
Full marks2/2

The control unit decodes instructions to determine what action is required.

Why: Linked point (1) and development (1): decodes instructions and determines the required action.

Some marks1/2

The control unit controls the fetch stage of the cycle.

Why: Point only (1): controls the fetch stage, but no linked development.

No marks0/2

The control unit carries out arithmetic and logical operations on data.

Why: No creditworthy point: describes the role of the ALU, which the mark scheme rejects.

3Discuss6 marksLow and High Level Languages Swap Remove

A software company is writing a new program that will be sold to users who have different types of computer. The program does not need to control the hardware of the computer directly. The company must decide whether to write the program in a high-level language or a low-level language.

Discuss whether the company should use a high-level language or a low-level language to write this program.

Your answer should consider:

  • machine independence
  • processor specificity
  • how the code is translated for each type of computer.
[6 marks]
Mark scheme

Indicative content

Machine independence

  • A high-level language is machine independent, so the same source code can be run on different types of computer with few or no changes.
  • The company can write the program once and sell it to users with different computers, without rewriting the code for each type of computer.
  • Only one version of the program needs to be written and maintained, so development takes the company less time.

Processor specificity

  • A low-level language is processor-specific, so a program written for one processor will not run on a different processor without being rewritten.
  • Assembly language instructions depend on the instruction set of the particular processor, so the company would need a separate version of the program for each type of computer.
  • Writing a separate low-level version for every type of computer would take the company much longer than writing one high-level program.
  • Low-level code gives direct control of the hardware of one processor, so it is better suited to device drivers than to a program that must run on many different computers.

Translation

  • High-level source code is translated for each type of computer by a compiler or an interpreter, so one version of the source code is enough for all the users.
  • Assembly language is translated into machine code by an assembler, and the assembler produces machine code for one specific processor only.
  • Machine code is already in a form that one particular processor can execute directly, but the same machine code will not run on a different processor.
  • Each high-level statement translates into several machine code instructions, so the programmer does not need to know the instruction set of the processor.

Levels

  • Level 0 (0 marks): No rewardable content.
  • Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
  • Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
  • Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Additional guidance

  • Level 3 responses must cover both high-level machine independence and low-level processor specificity, with the effect on the company's decision.
  • Do not award low-level language, assembly language or machine code as portable, or 'high-level languages are written in English/like English' as a reason for machine independence.
Example answers and how they were marked
Full marks6/6

A high-level language is machine independent, so the company can write the program once and it will run on different types of computer with few or no changes. A different compiler is used for each type of processor to translate that same source code into the machine code for that computer, so the company can sell one program to all of its users. A low-level language is processor-specific, so a program written in assembly for one processor will not run on a different one. The assembler produces machine code for one particular instruction set, so the company would need to write a separate version for each type of computer, which would take much longer. As the program does not need to control the hardware directly, the company should use a high-level language.

Why: Develops high-level machine independence with the compiler translating for each processor, and low-level processor specificity with the assembler producing machine code for one instruction set, both applied to the company's decision, in a coherent and sustained argument: Level 3, 6 marks.

Some marks3/6

A high-level language is machine independent, so the company can write the program once. A different compiler is used for each type of computer to translate the code, so users with different computers can all run the same program. A low-level language is processor-specific, so it would not be as suitable for the company.

Why: Machine independence is linked to the compiler and applied to the users, but processor specificity is only asserted and no translation of low-level code is given, so the reasoning is not sustained: Level 2, 3 marks.

Some marks1/6

High-level languages are machine independent because they are written in English, so the company can sell the program to anyone. Low-level languages are machine code, so they can be translated to run on any type of computer.

Why: One basic point that high-level languages are machine independent, applied by selling to anyone (1). 'Written in English' is not a reason for machine independence and low-level code is not portable, so neither is credited: Level 1, 1 mark.

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