AQA GCSE Computer Science Paper 2: Computing concepts November 2021 question paper 8525/2

Convert the decimal number 220 into binary.

Convert the hexadecimal number AD into binary.

You should show your working.

Convert the hexadecimal number 1A into decimal.

What is the largest hexadecimal number that can be represented in binary using 8 bits?

Which of the following is a reason why hexadecimal is used instead of binary?

Shade one lozenge.

Figure 1 shows a value represented as a bit pattern.

Figure 1

1 0 1 1 0 0 0 0

A binary shift can be used to divide the value in Figure 1 by 4.

What is the result of this shift?

Your answer must be in binary.

Eight minutes of sound has been digitally recorded. The sampling rate used was 25 000 Hertz and the sample resolution used was 4 bits.

Calculate the minimum file size for the recording. Give your answer in megabytes.

You should show your working.

Explain what effects increasing the sampling rate would have on the recording.

Shade two lozenges to show which of the following are functions of an operating system.

Define the term application software.

Give two examples of application software. You must not use brand names in your answer.

Example 1

Example 2

This description of how a magnetic hard disk drive works is partially correct but contains some errors:

‘A magnetic hard disk spins very quickly. The surface of the disk has a groove on it where data is stored. There is a needle that runs along the groove and detects bumps. One of the components of the drive is a read/write head.’

Describe three factual errors in the description.

State one correct fact in the description.

Three factors that affect the performance of a CPU are:

• clock speed

• number of processor cores

• cache size.

Explain how each of these factors affects CPU performance.

Clock speed

Number of processor cores

A farmer uses an automated system to indicate if soil conditions are right for planting.

The conditions are right for planting if the soil is:

• warm

• wet

• the correct acidity.

Figure 2 shows the logic circuit for this system.

The inputs to the system are:

Soil temperature (T): 0 if the soil is cold 1 if the soil is warm.

Soil moisture (M): 0 if the soil is dry 1 if the soil is wet.

Soil acidity (A): 0 if the soil is the correct acidity 1 if the soil acidity needs adjusting.

The output (P) is: 0 if the conditions for planting have not been met 1 if the conditions for planting have been met.

State the type of logic gate shown in Figure 3.

The farmer wants to modify the system so that it will indicate that the soil conditions are right for planting if at least one of the three conditions has been met.

Describe changes that could be made to the logic circuit in Figure 2 to allow this to happen.

Describe two differences between an embedded system and a non-embedded system.

Define the term computer network.

Explain how a firewall can be used to improve the security of a computer network.

Authentication and MAC address filtering can be used to improve network security.

Explain how one of these security methods works.

Ring your chosen security method:

Authentication
MAC address filtering

How it works

Several companies produce microchips that can be implanted in humans. Thousands of people around the world have voluntarily had these microchips implanted in their hands. These tiny microchips are the size of a grain of rice. They can be a form of identification and can store a range of personal data.

Describe how human microchip implants might be used when travelling or visiting places away from home.

In your answer you should include:

• potential uses

• advantages to the person who has the implant

• legal and ethical considerations of human chip implants.

Explain one data privacy concern an organisation would need to consider when setting up a wireless network.

Figure 4 shows a black and white image.

The image shown in Figure 4 could be compressed using Run Length Encoding (RLE). The RLE for the image in Figure 4 is B15 W9.

Figure 5 shows another black and white image.

Give the RLE for the image shown in Figure 5.

The RLE will be represented using binary, with one bit representing the colour (W = 1, B = 0) followed by seven bits representing the frequency.

Give the binary representation of the RLE: B15 W9

Table 1 is a frequency table that contains the frequency of characters in a string.

Use the frequencies given in Table 1 to draw a Huffman tree that represents the string.

Table 2 shows the Huffman codes for the characters used in the string PIEDPIPER

Calculate how many bits would be saved if the phrase PIEDPIPER was encoded using the Huffman codes shown in Table 2, rather than using ASCII.

You should show your working.

Number of bits saved

Table 3 shows screenshots of three different security measures.

Tick the box next to the CAPTCHA screenshot.

Give three examples of when it would be suitable to use a CAPTCHA system.

Shade the two lozenges that are examples of social engineering.

Table 4 shows three layers of the TCP/IP model and some protocols that operate at each of these layers.

Describe the role of one protocol from each layer in Table 4. You must state which protocol you are describing.

Application layer protocol

Transport layer protocol

Internet layer protocol