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Edexcel GCSE Computer Science (1CP2) Exam Questions

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4 questions · 13 marks

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1Short recall2 marksStored Program Computers Swap Remove

Computers use the von Neumann stored program concept.

Define the term stored program concept.

[2 marks]
Mark scheme

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

  • Program instructions are stored in main memory/RAM (1)
  • The data used by the program is stored in main memory/RAM (1)
  • The CPU fetches/reads instructions from main memory to execute them (1)
  • The program can be run without the instructions being input again (1)

Allow 'the program is stored in memory' for one mark.

Do not accept answers about programs being stored on secondary storage, such as a hard disk or USB memory stick.

Do not accept answers that only describe the von Neumann architecture (e.g. having a CPU and memory) without stating that instructions are stored in main memory.

Example answers and how they were marked
Full marks2/2

Both the program instructions and the data the program uses are held in the same main memory, and the CPU fetches these instructions from memory to execute them.

Why: Instructions stored in main memory (1) and the CPU fetches instructions from memory to execute them (1).

Some marks1/2

Program instructions are stored in main memory.

Why: Instructions stored in main memory (1). No second point about data being stored in the same memory or about the CPU fetching instructions.

No marks0/2

The program is saved on the hard disk so that it can be loaded into RAM when the user runs it.

Why: A near-miss about secondary storage, which the mark scheme says not to accept; the stored program concept is about instructions being held in main memory.

2Short recall2 marksUnits & Conversion Swap Remove

Data storage is measured in binary multiples.

Define the term bit.

[2 marks]
Mark scheme

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

  • A binary digit (1)
  • Has the value 0 or 1 (1)
  • The smallest unit of data storage (1)
  • A single 0 or 1 (1)

Allow binary digit/binary place value for binary digit

Allow a single binary digit for a single 0 or 1

Do not accept a group of 8 bits/half a nibble of 4 bits, which describe a byte or a nibble

Do not accept a binary number/binary on its own

Example answers and how they were marked
Full marks2/2

A binary digit that can have the value 0 or 1.

Why: A binary digit (1) and has the value 0 or 1 (1).

Some marks1/2

It is the smallest unit of data storage.

Why: Smallest unit of data storage (1), but does not state that it is a binary digit or that it has the value 0 or 1.

No marks0/2

A group of 8 bits.

Why: Describes a byte, not a bit; no creditworthy point and named in the Do not accept line.

3Calculate3 marksAdding Binary Numbers Swap Remove

Binary patterns can represent numbers.

(a)

Complete the table to show the 8-bit result of the binary addition.

[2 marks]
1286432168421
11011011
11011100
Mark scheme

Award one mark for each correct nibble in the correct order:

  • 1011 (1)
  • 0111 (1)

0 marks if the response is not 8-bit binary.

Ignore a carry shown beyond the eighth bit.

Example answers and how they were marked
Full marks2/2

1011 0111

Why: 219 + 220 = 439, which needs 9 bits; the 8 bits that are kept are both correct (2).

Some marks1/2

0000 0111

Why: Forgets to carry the 1s. The second nibble is correct (1); the first is not.

No marks0/2

1101 1111

Why: Never carries. Neither nibble is correct.

(b)

State the name of the error that occurs when this addition is carried out.

[1 mark]
Mark scheme

Award one mark for:

  • overflow (error) (1)
Example answers and how they were marked
Full marks1/1

Overflow

Why: The result needs more bits than are available (1).

No marks0/1

Underflow

Why: A near miss: the result is too big for 8 bits, not too small.

No marks0/1

A syntax error

Why: A syntax error is a mistake in a program's code, not in arithmetic.

4Discuss6 marksFile Management Swap Remove

A small business has one computer with a single hard disk. Two employees save documents and photographs to it every day. The operating system manages the disk.

Discuss why the operating system needs to manage where files are stored on the disk.

Your answer should include:

  • how the operating system allocates disk space when a file is saved
  • how the operating system keeps track of each file
  • what could happen if the operating system did not manage files
[6 marks]
Mark scheme

Indicative content

Allocating space

  • The operating system checks that there is enough free space before a file is saved, so a large photograph does not make the save fail.
  • The operating system finds free space on the disk and allocates it to the new file, so the file's data has somewhere to be written.
  • Disk space is allocated so that a file is not written on top of data that already belongs to another file.
  • When a file is deleted, the operating system marks its space as free so it can be used again by the next document that is saved.

Keeping track

  • The operating system keeps a record of the name, size and location of every file, so it knows where each file is stored.
  • The record is updated whenever a file is saved, renamed or deleted, so it still matches what is on the disk.
  • The operating system uses this record to find a file again, so an employee can open a document or photograph that was saved earlier.
  • The record lets the operating system tell the two employees' documents and photographs apart, even though they are all on the same disk.

Without this management

  • Two files could be given the same space, so one document would overwrite another and the work would be lost.
  • The operating system would not know where a file is stored, so a saved document could not be found and opened again.
  • Space used by deleted files might never be freed, so the disk would fill up and new files could not be saved.

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)

Level 3 responses must cover both the allocation of space and the tracking of files, with at least one consequence of no management linked to its cause. Reference to a file being split across blocks that are not next to each other, or to the record holding the location of each block, is Level 3 detail and is not required.

Basic, unlinked points with no application to the business's documents or photographs, and a consequence such as 'files would be lost' with no cause given, are limited to Level 1; to reach Level 2 a point must be linked to a reason (for example, the record is kept so a document can be found again) and be applied to the context. Do not accept defragmentation, process scheduling, user management, peripheral management, or backup and antivirus scanning, as file management.

Example answers and how they were marked
Full marks6/6

Before a document is saved, the operating system checks that there is enough free space on the single disk, so a large photograph cannot make the save fail. It then finds free space and allocates it to the new file, making sure it does not write over data that already belongs to another file. The operating system keeps a record of the name, size and location of every file and updates it whenever a file is saved or deleted. It uses this record to find a file again, so an employee can open a document that was saved earlier. Without this, the two employees could be given the same space, so one document would overwrite the other, or the operating system would not know where a file is stored and the business could not find its work again.

Why: Covers both allocation (free space check, free space given to the file, no overwriting) and tracking (record of name, size and location, updated on save, used to find the file), applies it to the business's single disk and its two employees' documents and photographs, and links the consequences of no management to their causes: Level 3.

Some marks2/6

The operating system decides where on the disk a file is saved. It also keeps a record of where each file is stored. Without this, files would be lost.

Why: Two basic points are made: space is allocated when a file is saved, and a record of where each file is stored is kept. Neither is linked to a reason, there is no application to the business's documents and photographs, and 'files would be lost' is given with no cause: Level 1, top of the level.

Some marks1/6

The operating system puts files in the right place so the disk does not get full. It also defragments the disk to make the files smaller.

Why: One basic point about the operating system placing files on the disk so it does not fill up (Level 1). Defragmentation is not file management and does not make files smaller, so it is not credited: Level 1.

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