Build a practice paper from 693 exam-style questions, each with its mark scheme and example answers. Print it, or answer it on paper and then open the mark schemes. Or browse the questions by topic.
3 questions · 5 marks
Computers manipulate binary patterns.
Convert the binary pattern 1110 0000 to denary.
Award one mark for:
224
Why: Correct: 128 + 64 + 32 = 224 (1).
7
Why: Reads the place values from the wrong end (the left-hand bit as 1), so the value is wrong.
3
Why: Counts the 1s instead of adding their place values.
ASCII is a character set that uses 7 bits to represent each character.
Give two limitations of 7-bit ASCII when it is used to represent text.
Award one mark for any of the following up to a maximum of two marks:
Award a maximum of one mark for the last three bullets, as they are all examples of characters that fall outside the 128 ASCII codes.
Allow 'it can only represent 128 characters, so some characters are missing' for the first bullet.
Do not accept 'it uses 7 bits' / 'it only uses 7 bits' on its own, without saying what this limits.
Do not accept 'it can only store a limited amount of text' / 'it can only store short messages', as 7 bits limits the number of characters available, not the length of a message.
Do not accept 'it can only represent the characters in the ASCII character set', as this repeats the question.
Do not accept 'it is old/out of date' or 'it cannot store numbers'.
Only 128 different characters can be represented, so it cannot store characters from other languages such as Greek.
Why: 128 character limit (1) and characters from other languages (1); two separate creditworthy limitations.
It cannot show accented characters like é and it only uses 7 bits.
Why: Accented characters (1); 'only uses 7 bits' is not qualified, so scores 0.
It only uses 7 bits, so it can only store a small amount of text.
Why: Scores 0: text length is not a limitation of 7-bit ASCII, and 'only uses 7 bits' is unqualified; both Do not accept lines apply.
A student has a large number of photographs stored on a computer.
Describe the purpose of data compression software.
Award up to two marks for a linked description such as:
Do not accept 'it compresses the files' on its own, as this repeats the question.
Do not accept responses about protecting files from malware/viruses or about deleting files.
It makes the files smaller so that they use less storage space on the computer and more of them fit on the disk.
Why: The point (1) and a linked development giving the benefit (1).
It makes files smaller.
Why: This is the point (1) but there is no development of what the smaller size leads to, so only one mark.
It protects the files from viruses so that they cannot be damaged.
Why: This describes anti-malware software, which the mark scheme does not accept; no creditworthy point is made.
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