Edexcel GCSE Computer Science (1CP2) Exam Questions

Award one mark for any of the following:

• Increase the sample rate / take more samples per second (1)
• Increase the bit depth/sample resolution / use more bits per sample (1)
• Decrease the sample interval (1)

Do not accept increase the amplitude/volume

Do not accept decrease the sample rate / increase the sample interval

Award one mark for any of the following:

• The number of bits per pixel (1)
• The number of bits used to represent/store the colour of each pixel (1)

Allow bit depth

Do not accept the number of colours a pixel can have on its own

Do not accept the number of pixels in the image (this is the resolution/image size)

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

• The computer looks up the character in the ASCII character set/table (1) to find the code that represents it (1)
• Each character has its own unique ASCII code (1) so the letter A is converted to and stored as a 7-bit binary pattern (1)
• ASCII uses 7 bits for each character (1) so A is stored as its ASCII code 1000001 (binary) / 65 (denary) (1)

The second mark requires a linked expansion, so a point on its own (e.g. 'A has the code 65') can only earn one mark.

For both marks, the expansion must follow/associate with the statement.

Accept an 8-bit pattern with a leading 0 (e.g. 01000001) as the binary code for A.

Do not accept 'the character is stored as text' without saying it is changed into a code/binary.

Do not accept a binary value on its own (e.g. 1000001) without saying that it is the ASCII code/that the character is converted to it.

Indicative content

How characters are mapped to codes

• Each character in a book title or author name is given a unique 7-bit binary code from the ASCII character set.
• The letter A, for example, is stored as the code 1000001 and the letter B as 1000010, so the catalogue can store letters as binary.
• Uppercase letters, lowercase letters, digits, punctuation and the space character each have their own ASCII code.
• The same character always uses the same code, so the text can be stored and read back correctly by the library system.

Why 7 bits are used for each character

• Seven bits give 2 to the power of 7, which is 128 different bit patterns, and this is enough to represent the letters, digits and punctuation needed in the catalogue.
• A standard keyboard has around 98 characters, so 6 bits would give only 64 codes and would not be enough.
• Using a fixed 7 bits per character means every character takes the same amount of storage, which makes the catalogue file simple to process.

Benefits of using ASCII for the catalogue

• ASCII is a standard character set, so the catalogue data can be exchanged between different computers and software.
• Author names and titles entered on one system will display correctly on another system that uses ASCII.
• ASCII uses only 7 bits per character, so the catalogue takes less storage than a character set that uses more bits.
• It is simple to encode and decode because each character has a single fixed code.

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)

Do not accept 8 bits or 256 characters as features of 7-bit ASCII; these are extended ASCII.