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3 questions · 4 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Do not accept 'it is old/out of date' or 'it cannot store numbers'.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 company backs up its files to an external hard drive.
Give one reason why the company compresses the files before backing them up.
Award one mark for any of the following:
Do not accept 'makes the files more secure' or 'encrypts the files'.
The compressed files take up less storage space, so more files can be backed up.
Why: The files take up less storage space (1).
It reduces the amount of disk fragmentation.
Why: Near-miss: compression does not reduce disk fragmentation.
It encrypts the files so they are safer if the drive is stolen.
Why: Misconception: compression does not encrypt files, and security is not accepted.
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