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4 questions · 7 marks
Binary, denary and hexadecimal patterns represent numbers.
Convert the binary pattern 1110 1100 to denary.
Award one mark for:
236
Why: Correct: 128 + 64 + 32 + 8 + 4 = 236 (1).
55
Why: Reads the place values from the wrong end (the left-hand bit as 1), so the value is wrong.
5
Why: Counts the 1s instead of adding their place values.
Images and sound can be stored using lossy compression.
Define the term lossy compression.
Award one mark for any of the following up to a maximum of two marks:
Allow 'some data is deleted/discarded and cannot be recovered' for the second mark.
Do not award the first mark where the response also states that no data is lost.
Do not accept 'removes repeated data' (this describes lossless compression).
Lossy compression reduces the size of a file by permanently removing some data, so the original cannot be restored exactly.
Why: Reduces the size of a file (1); permanently removes some data (1); maximum two marks awarded.
It makes a file smaller.
Why: Reduces the size of a file (1); no reference to data being permanently lost.
It makes a file smaller without losing any of the data.
Why: States that no data is lost, which describes lossless compression; the first mark is not awarded.
A computer can be used by more than one person.
Describe how an operating system uses access rights to protect each user's files.
Award up to two marks for a linked description such as:
Do not accept responses about asking for a password/username, as this checks who the user is, not what they are allowed to do.
Do not accept 'files are protected/safe' or 'access rights protect files' without saying how access is limited (e.g. read-only access, permissions for different users).
A user can be given read-only access to a file, so they can open it but cannot edit or delete it.
Why: Read-only/read access point (1) and linked development that the user cannot edit/delete the file (1).
A user can be given read-only access to a file.
Why: Read-only/read access point (1); no development saying what this prevents, such as being unable to edit/delete the file (0).
The operating system asks for the password again before the file opens.
Why: Describes asking for a password, which checks who the user is, not access rights to the file; no creditworthy point.
Binary patterns can represent numbers.
Convert the denary number 199 to 8-bit binary.
Award one mark for each correct nibble in the correct order:
0 marks if the response is not 8-bit binary.
1100 0111
Why: 199 = 128 + 64 + 4 + 2 + 1: both nibbles are correct (2).
1100 1000
Why: Converts 200 instead (a slip in adding up the place values). The first nibble is correct (1); the second is not.
1110 0011
Why: The bits are written in reverse, smallest place value first. Neither nibble is correct.
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