AQA A Level Computer Science Paper 2: Written exam June 2025 question paper 7517/2

Figure 1 shows the classification of various types of software and some examples of these types.

Figure 1

Complete Table 1 by naming the correct types of software that should be placed at positions 1 to 4 in Figure 1.

One function of the operating system is to allocate I/O devices to competing processes.

Describe two other functions of an operating system.

Function 1

Function 2

Software can be developed using a low-level language or a high-level language.

Describe the advantages of writing programs using a high-level language.

A sound file, produced by sampling sound, requires 1.5 megabytes of storage space.

The sound file has a duration of 50 seconds and was recorded at a sample rate of 20 000 samples per second (Hertz).

Calculate the sample resolution that was used when the sound was sampled.

Describe the principles of operation of an analogue to digital converter (ADC).

Explain one reason why a digital sound file that has been recorded using sampling may not accurately represent the original analogue signal produced by the microphone.

One advantage of representing a piece of music using MIDI instead of as sampled sound is that the file produced requires less storage space.

Explain why.

Describe the principles of operation of an optical disk.

In your response, you should cover how data is represented on a disk and how the data would be read.

State two reasons why most modern computers do not have an optical disk drive.

Reason 1

Reason 2

It is difficult to write and enforce laws relating to the use of computers.

Explain why.

Explain why a client-server network would be more suitable for use in a school than a peer-to-peer network.

A school uses a relational database to store information about merits that are given to students. A merit is an award made for outstanding work or conduct.

At the end of each term, prizes are awarded to the students who achieve the most merits.

The database contains the four relations shown in Figure 2.

The Student relation stores information about the students who attend the school. An example of the data stored about a student is:

The Teacher relation stores information about the teachers who work at the school and who award merits to students.

The Merit relation stores information about the merits that teachers have awarded to students, when they were awarded and for what reason.

The Term relation stores information about the dates of each term. An example of the data stored about a term is:

The StudentID, TeacherID, MeritID, YearGroup and TermYear attributes are all numeric values.

When the Merit relation was first designed, it did not contain the MeritID field. Instead, the values in the StudentID, TeacherID and DateAwarded attributes were used together as a composite entity identifier.

Describe the limitation that would have occurred if the entity identifier for the Merit relation consisted of the StudentID, TeacherID and DateAwarded attributes.

The diagram below shows three of the entities from the school merit database.

Draw the relationships that exist between the three entities shown on the diagram.

You must clearly show the degree of each relationship.

Figure 2 is repeated below to help you answer Questions 06.3 and 06.4 without having to turn back in the question paper.

A new student has joined the school. The student is called Ethan Smith and their year group is 7. They are placed in Hulme house and given the StudentID number 17423.

Write SQL code to add the student’s details to the Student table.

At the end of the Spring term of 2025, the school needed to identify the students who achieved merits during the term, so that prizes could be awarded to them.

The dates of the term are stored in the Term table.

Write a query that will list all the merits that were awarded during the term.

For each merit on the list, the first name and last name of the student awarded the merit should be included, together with the reason the merit was awarded.

The merits should appear on the list in order of the StudentID of the students that they were awarded to, with merits for the student with the lowest StudentID at the start of the list.

The merits database can be accessed on any computer within the school.

It is possible that two users might try to edit the same record simultaneously.

Describe how two users trying to edit the same record could cause a problem if the database system did not implement a method to manage concurrent access.

State the stored program concept.

Describe the roles of the following three components of a processor.

General purpose registers

When the immediate addressing mode is used:

• the value in Operand C in Figure 3 represents a numeric value that will be processed by the ADD instruction

• the value in Operand C is represented as a two’s complement binary integer.

In decimal, calculate the range of numbers that Operand C can represent.

The Internet Protocol version 4 (IPv4) addressing system does not provide enough unique addresses for every device that is connected to the Internet.

This is being addressed in the long term by the replacement of IPv4 with IPv6.

In the short term, the use of public and private IP addresses, NAT and DHCP is helping to deal with this problem.

Explain:

• why IPv4 does not provide enough unique addresses and how IPv6 will overcome this problem

• the difference between a public (routable) and a private (non-routable) IP address

• how NAT works and how it helps to deal with this problem

• how DHCP works and how it helps to deal with this problem.

Figure 4 shows a logic circuit. The circuit has seven inputs and two outputs. The inputs B₆ to B₀ represent the ASCII code of a character, where B₆ is the most significant bit and B₀ is the least significant bit. The circuit outputs are Q₁ and Q₂. The outputs of six of the gates in the circuit have been labelled U, V, W, X, Y and Z.

Figure 5 shows the ASCII code for printable characters.

Figure 4 is repeated below to help you answer Questions 09.2 and 09.3 without having to turn back in the question paper.

Describe the purpose of the outputs Q₁ and Q₂ of the circuit in Figure 4.

Shade one lozenge to indicate which of the Boolean equations correctly represents

State two reasons why data is often compressed.

Reason 1

Reason 2

Two different methods of compressing data are run length encoding (RLE) and dictionary-based methods.

Explain why RLE is more suitable for compressing images and dictionary-based methods are more suitable for compressing text.

Shade all of the lozenges for the statements that are true about the fibonacci function in Figure 6.

Shade one lozenge to indicate the function type of the fibonacci function in Figure 6.

Explain why the recursive method used by the code in Figure 6 is not an efficient method of calculating the n th term in the Fibonacci sequence.

Describe what partial function application is.

A computer represents numbers using a normalised floating point representation with an 8-bit mantissa and a 6-bit exponent, both stored using two’s complement, as shown in Figure 7.

Five different bit patterns that are stored in this computer’s memory are listed in Figure 7 and are labelled with the letters A to E. Four of the bit patterns are valid normalised floating point numbers and one is not.

Shade one lozenge to indicate which bit pattern (A – E) in Figure 7 does not represent a normalised value.

Shade one lozenge to indicate which bit pattern (A – E) in Figure 7 shows the most negative normalised value that can be represented.

State one reason why values stored using a floating point representation are usually normalised.

Question parts 12.4 and 12.5 use a normalised floating point representation with an 8-bit mantissa and a 6-bit exponent, both stored using two’s complement.

Figure 8 shows a floating point representation of a number:

Calculate the decimal equivalent of the number in Figure 8.

Express your answer to at least four decimal places or as a fraction.

You should show your working.

Calculate the relative error that occurred when you represented 43 057 152 as closely as possible in question part 12.5.

You should show your working.

Express your answer as a percentage to at least four decimal places.

Using the rules of Boolean algebra, simplify the following Boolean expression.

You must show your working.

Working