Actual 2025 AQA A-LEVEL COMPUTER SCIENCE 7517/2 Paper 2 Merged Question Paper + Mark Scheme
Answer all questions. box
0 1 Anti-virus software and user training are measures that can be used to reduce the
threat posed by viruses.
Describe four other measures that can be used to reduce the threat posed by
viruses.
A digital camera takes photographs that are 4000 pixels wide by 3000 pixels tall and
can contain up to 16 777 216 different colours.
Calculate the size of one image in megabytes.
How many images, taken using the camera referred to in Question 02.1, could be
stored on a 256 gigabyte memory card?
You should assume that all of the storage space on the memory card is available to
store image data.
Round your answer down to the nearest whole number.
When a digital camera takes a photograph, an array of photosensors produces box
analogue voltages representing the amount of light falling on each photosensor. An
analogue-to-digital converter then converts these analogue voltages into digital
values. These digital values are used to create the pixel data for the bitmap image.
0 2 . 3 Explain why the voltages produced by the photosensors are considered to be
analogue and why the pixel data is considered to be digital. 
An image is 20 pixels wide by 30 pixels tall. The colour of each pixel is represented
using one byte.
Here is a row of data from the original image. The colour of each of the 20 pixels is
shown as a decimal value, with commas used to separate the data for the different
pixels:
24, 24, 24, 253, 254, 255, 76, 76, 76, 80, 82, 0, 0, 9, 223, 223, 224, 220, 76, 76
The image is to be compressed using Run Length Encoding (RLE). The RLE method
used will:
• represent the length of a run using one byte
• represent a colour using one byte.
In decimal, the RLE for the colour of the first four pixels would be:
3, 24, 1, 253
0 2 . 4 Calculate how much memory the row of pixels will take up before and after it has
been encoded using RLE.
[1 mark]
Memory before RLE (bytes)
Memory after RLE (bytes)