AQA A Level Computer Science Exam
With 100% Correct Answers
What are the 6 main categories for numbers? What are their symbols? - correct answers
✔✔Real (ℝ), rational (ℚ), integer (ℤ), natural (ℕ). Irrational. Ordinal.
What are the 3 main number systems? What are their bases? - correct answers
✔✔Decimal/Denary: Base-10 Binary: Base-2 Hexadecimal: Base-16
How are hexadecimal values shown? - correct answers ✔✔Each hexadecimal represents \
(16^{n-1}\), with values \(10-15\) being shown by A-F.
How do you convert between hexadecimal to denary/binary? - correct answers ✔✔D → H:
divide number by 16, use remainders. If remainder >\(16\), divide again. B → H: split bytes into
nibbles, convert to denary, convert to hex, put values back together
Why is hexadecimal/denary preferred over binary for some information (e.g. colours/MAC
address)? - correct answers ✔✔Shorter to type or write and easier to remember than a long
string of binary digits.
Which data storage prefixes denote powers of 10, and which denote powers of 1024? What are
their symbols? - correct answers ✔✔Kilo (k), Mega (M), Giga (G), Tera (T) Kibi (Ki), Mebi (Mi),
Gibi (Gi), Tebi (Ti)
What does ASCII stand for? What is it for? - correct answers ✔✔American Standard Code for
Information Interchange. Used to encode characters and symbols so they can be represented in
computers. 8 bits are used for encoding.
,Why can you not perform operations between numbers in different formats (string and
integer)? - correct answers ✔✔The binary values are different, therefore the operation would
not turn out as expected.
What is Unicode? Why would it be preferable to ASCII? What does it have in common with
ASCII? - correct answers ✔✔Another form of encoding characters. It uses variable encoding,
meaning that it can use different amounts of bits. To make usage easier, first 128 characters are
the same as the ASCII set.
What are four main causes of data not being transferred completely/correctly? What can this
lead to? - correct answers ✔✔Normal wear & tear on cables/connectors, synchronisation
issues, electrical interference, or power surges. Can lead to flipped bits in data.
What are the four main ways to check for errors in data transmission? - correct answers
✔✔Parity bits: odd/even number of bits is mandated. Carried out using the MSB. Not useful if
an even number of bits have flipped. Majority voting: data is sent over three times, and majority
of bits shown will be used. Not useful if the erroneous bits are in the majority. Check digits:
number at the end of a string that is formulated using the other values. Typically found in ISBNs.
Add the numbers, find remainder after dividing by 10 & subtract from 10 to get the check digit.
Checksum: total sum of bytes is calculated and sent with data in transmission. Recipient re-
calculates sum of bytes and compares to checksum to see if data has changed. If so, data is
resent. Used to verify credit card numbers.
What are the 4 main rules to binary addition? - correct answers ✔✔\(0+0=1\) \(0+1=1\) \
(1+1=0\), carry a 1. \(1+1+1=1\), carry a 1.
How does binary multiplication work? - correct answers ✔✔Multiply starting from LSB to MSB.
Shift one place each time you move to new value in the number (with LSB at zero shifts). Add up
the values found at the end.
,What is the maximum range of values that can be shown in signed/unsigned binary by using n
bits? - correct answers ✔✔Unsigned: \(0 \ \ \text{to}\ \ 2^n-1\) Signed: \(-(2^{n-1})\ \ \
text{to}\ \ 2^{n-1}-1\)
When does an overflow error occur in binary? - correct answers ✔✔When the decimal value
does not fit within the range representable in binary e.g. greater than 255 for unsigned binary
with 8 bits.
How do you find the negative of a number in binary? - correct answers ✔✔Write the positive of
the number in binary, then flip the bits. Add 1 to this to get the negative value.
How are fractional values represented in binary? - correct answers ✔✔A fixed/floating point is
used. The bits on the left of this are positive powers of 2, while bits on the right use negative
powers of 2, which are fractions.
What is the difference between a fixed and floating point? Which is better and why? - correct
answers ✔✔A fixed point will keep the number of bits representing positive and negative
powers the same, no matter what. A floating point will move based on the number that needs
to be represented. Both will increase accuracy but decrease maximum range, although a
floating point can change this by moving the point. So, a floating point is preferred.
What types of data are analogue and digital data? - correct answers ✔✔Analogue data is
continuous, while digital data is discrete.
How would a camera convert analogue light data to digital data to show an image? - correct
answers ✔✔The light intensity is measured and shown as an integer value. This is recorded in
an ADC, and is assigned to a pixel. Done as much as possible to have a high-quality image.
What are bitmapped graphics represented by? What are some bitmap image file types? -
correct answers ✔✔Bitmap images are made up of pixels. Common file types
include .jpg, .png, .gif, .bmp, .tif
, What determines the file size of a bitmap image? - correct answers ✔✔Resolution: height in
pixels * width in pixels Colour depth: number of bits assigned per pixel e.g. 3 bits per pixel.
Resolution * colour depth = file size in bits.
What is metadata? Give 4 examples: - correct answers ✔✔Metadata: data about files/data.
Examples include date created, owner of file, resolution, colour depth.
How is sound converted from analogue to digital, and vice versa? - correct answers ✔✔Sample
of the analogue signal is recorded by an amplifier, which quantises the data (giving wave heights
integer values). Data is encoded in binary. Reverse occurs to play sound.
Give an example of what may be an ADC or DAC: - correct answers ✔✔ADC: microphone DAC:
loudspeaker
State two things needed for sound quality in recordings: - correct answers ✔✔Sample rate: the
number of times per second a sample is measured. Measured in Hertz. Audio bit depth: number
of bits available to determine the amplitude of the wave at the sample point.
How is file size determined in sound files? - correct answers ✔✔Sample rate * sample
resolution * length in seconds = file size in bits sample resolution = bit audio depth
Why does using stereo sound result in larger file sizes? - correct answers ✔✔The sample has to
be recorded for each channel, doubling the file size if two channels are used e.g. left & right
"What is Nyquist's Theorem? Why is it important?" - correct answers ✔✔"Nyquist's Theorem
dictates that the lowest sampling rate for a recording must be at least twice the maximum
frequency of the sample to replicate the original soundwave. Used because sounds are usually
made up of different frequencies. Having the sampling rate above twice the highest frequency
ensures each peak and trough of the wave is picked up, for accuracy."
With 100% Correct Answers
What are the 6 main categories for numbers? What are their symbols? - correct answers
✔✔Real (ℝ), rational (ℚ), integer (ℤ), natural (ℕ). Irrational. Ordinal.
What are the 3 main number systems? What are their bases? - correct answers
✔✔Decimal/Denary: Base-10 Binary: Base-2 Hexadecimal: Base-16
How are hexadecimal values shown? - correct answers ✔✔Each hexadecimal represents \
(16^{n-1}\), with values \(10-15\) being shown by A-F.
How do you convert between hexadecimal to denary/binary? - correct answers ✔✔D → H:
divide number by 16, use remainders. If remainder >\(16\), divide again. B → H: split bytes into
nibbles, convert to denary, convert to hex, put values back together
Why is hexadecimal/denary preferred over binary for some information (e.g. colours/MAC
address)? - correct answers ✔✔Shorter to type or write and easier to remember than a long
string of binary digits.
Which data storage prefixes denote powers of 10, and which denote powers of 1024? What are
their symbols? - correct answers ✔✔Kilo (k), Mega (M), Giga (G), Tera (T) Kibi (Ki), Mebi (Mi),
Gibi (Gi), Tebi (Ti)
What does ASCII stand for? What is it for? - correct answers ✔✔American Standard Code for
Information Interchange. Used to encode characters and symbols so they can be represented in
computers. 8 bits are used for encoding.
,Why can you not perform operations between numbers in different formats (string and
integer)? - correct answers ✔✔The binary values are different, therefore the operation would
not turn out as expected.
What is Unicode? Why would it be preferable to ASCII? What does it have in common with
ASCII? - correct answers ✔✔Another form of encoding characters. It uses variable encoding,
meaning that it can use different amounts of bits. To make usage easier, first 128 characters are
the same as the ASCII set.
What are four main causes of data not being transferred completely/correctly? What can this
lead to? - correct answers ✔✔Normal wear & tear on cables/connectors, synchronisation
issues, electrical interference, or power surges. Can lead to flipped bits in data.
What are the four main ways to check for errors in data transmission? - correct answers
✔✔Parity bits: odd/even number of bits is mandated. Carried out using the MSB. Not useful if
an even number of bits have flipped. Majority voting: data is sent over three times, and majority
of bits shown will be used. Not useful if the erroneous bits are in the majority. Check digits:
number at the end of a string that is formulated using the other values. Typically found in ISBNs.
Add the numbers, find remainder after dividing by 10 & subtract from 10 to get the check digit.
Checksum: total sum of bytes is calculated and sent with data in transmission. Recipient re-
calculates sum of bytes and compares to checksum to see if data has changed. If so, data is
resent. Used to verify credit card numbers.
What are the 4 main rules to binary addition? - correct answers ✔✔\(0+0=1\) \(0+1=1\) \
(1+1=0\), carry a 1. \(1+1+1=1\), carry a 1.
How does binary multiplication work? - correct answers ✔✔Multiply starting from LSB to MSB.
Shift one place each time you move to new value in the number (with LSB at zero shifts). Add up
the values found at the end.
,What is the maximum range of values that can be shown in signed/unsigned binary by using n
bits? - correct answers ✔✔Unsigned: \(0 \ \ \text{to}\ \ 2^n-1\) Signed: \(-(2^{n-1})\ \ \
text{to}\ \ 2^{n-1}-1\)
When does an overflow error occur in binary? - correct answers ✔✔When the decimal value
does not fit within the range representable in binary e.g. greater than 255 for unsigned binary
with 8 bits.
How do you find the negative of a number in binary? - correct answers ✔✔Write the positive of
the number in binary, then flip the bits. Add 1 to this to get the negative value.
How are fractional values represented in binary? - correct answers ✔✔A fixed/floating point is
used. The bits on the left of this are positive powers of 2, while bits on the right use negative
powers of 2, which are fractions.
What is the difference between a fixed and floating point? Which is better and why? - correct
answers ✔✔A fixed point will keep the number of bits representing positive and negative
powers the same, no matter what. A floating point will move based on the number that needs
to be represented. Both will increase accuracy but decrease maximum range, although a
floating point can change this by moving the point. So, a floating point is preferred.
What types of data are analogue and digital data? - correct answers ✔✔Analogue data is
continuous, while digital data is discrete.
How would a camera convert analogue light data to digital data to show an image? - correct
answers ✔✔The light intensity is measured and shown as an integer value. This is recorded in
an ADC, and is assigned to a pixel. Done as much as possible to have a high-quality image.
What are bitmapped graphics represented by? What are some bitmap image file types? -
correct answers ✔✔Bitmap images are made up of pixels. Common file types
include .jpg, .png, .gif, .bmp, .tif
, What determines the file size of a bitmap image? - correct answers ✔✔Resolution: height in
pixels * width in pixels Colour depth: number of bits assigned per pixel e.g. 3 bits per pixel.
Resolution * colour depth = file size in bits.
What is metadata? Give 4 examples: - correct answers ✔✔Metadata: data about files/data.
Examples include date created, owner of file, resolution, colour depth.
How is sound converted from analogue to digital, and vice versa? - correct answers ✔✔Sample
of the analogue signal is recorded by an amplifier, which quantises the data (giving wave heights
integer values). Data is encoded in binary. Reverse occurs to play sound.
Give an example of what may be an ADC or DAC: - correct answers ✔✔ADC: microphone DAC:
loudspeaker
State two things needed for sound quality in recordings: - correct answers ✔✔Sample rate: the
number of times per second a sample is measured. Measured in Hertz. Audio bit depth: number
of bits available to determine the amplitude of the wave at the sample point.
How is file size determined in sound files? - correct answers ✔✔Sample rate * sample
resolution * length in seconds = file size in bits sample resolution = bit audio depth
Why does using stereo sound result in larger file sizes? - correct answers ✔✔The sample has to
be recorded for each channel, doubling the file size if two channels are used e.g. left & right
"What is Nyquist's Theorem? Why is it important?" - correct answers ✔✔"Nyquist's Theorem
dictates that the lowest sampling rate for a recording must be at least twice the maximum
frequency of the sample to replicate the original soundwave. Used because sounds are usually
made up of different frequencies. Having the sampling rate above twice the highest frequency
ensures each peak and trough of the wave is picked up, for accuracy."
