2024_AQA: AS COMPUTER SCIENCE Paper 2 (merged Question paper and marking scheme): Tuesday 21 May 2024

2024_AQA: AS COMPUTER SCIENCE Paper 2 (merged Question paper and marking scheme): Tuesday 21 May 2024 Please write clearly in block capitals. Centre number Surname Forename(s) Candidate signature Candidate number I declare this is my own work. AS COMPUTER SCIENCE Paper 2 Tuesday 21 May 2024 Materials For this paper you must have:  a calculator. Instructions Afternoon Time allowed: 1 hour 30 minutes  Use black ink or black ball-point pen.  Fill in the boxes at the top of this page.  Answer all questions.  You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages.  If you need extra space for your answer(s), use the lined pages at the end of this book. Write the question number against your answer(s).  Do all rough work in this book. Cross through any work you do not want to be marked. Information  The marks for questions are shown in brackets.  The maximum mark for this paper is 75. Advice  In some questions you are required to indicate your answer by completely shading a lozenge alongside the appropriate answer as shown.  If you want to change your answer you must cross out your original answer as shown.  If you wish to return to an answer previously crossed out, ring the answer you now wish to select as shown. For Examiner’s Use Question Mark 1 2 3 4 5 6 7 8 9 10 11 TOTAL AS Computer Science Paper 2 - Key Areas to Revise Paper 2 focuses on practical problem-solving, algorithmic thinking, and understanding the theoretical concepts behind computer systems, programming, and data structures. It assesses your ability to apply theoretical knowledge to solve complex problems using algorithms and programming techniques. Key areas to revise include: 1. Advanced Programming Concepts:  Data Structures: Review important data structures like arrays, linked lists, stacks, queues, and trees. Be prepared to implement and manipulate these structures in code.  Algorithms: Focus on more complex algorithms beyond basic sorting and searching. You should be comfortable with: o Sorting Algorithms: Quick sort, merge sort, insertion sort, and their time complexities (Big O notation). o Searching Algorithms: Binary search (for sorted data) and linear search.  Recursion: Algorithm Efficiency: 2. Data Representation and Structures:  Binary and Hexadecimal Representation: Be comfortable with converting between binary, hexadecimal, and decimal systems. Understand how binary numbers are used to represent data (e.g., integers, floating point numbers).  Data Structures Implementation: Understand how to implement and work with more advanced data structures, including: o Stacks and Queues: Implementing and using stacks (LIFO) and queues (FIFO). o Trees: Study binary trees, binary search trees, and tree traversal algorithms (in-order, pre-order, post-order).  File Handling: 3. Problem Solving and Algorithm Design:  Developing Algorithms: Focus on developing algorithms for solving problems. Be prepared to break down a problem into smaller steps and design a solution using appropriate algorithms.  Pseudocode and Flowcharts: Practice writing pseudocode and flowcharts to represent algorithms  Optimization 4. Software Development and Testing:  Testing and Debugging: Understand how to write and apply test cases to verify the correctness of a program. Review common debugging techniques to locate and fix errors in code.  Error Handling & Version Control: 5. Computer Systems and Networks: 6. Databases and SQL: 7. Ethical, Legal, and Social Issues in Computing: By focusing on these areas, you will be well-prepared for AS Computer Science Paper 2, which will test your ability to solve complex problems, write efficient algorithms, and understand the theoretical aspects of computer systems, programming, and data structures. 7516/2 IB/G/Jun24/G4001/E11 2 Do not write outside the box Answer all questions in the spaces provided. IB/G/Jun24/7516/2 A ℂ B ℕ C ℚ D ℝ E ℤ 4 0 1 . 1 Describe the set of real numbers. [1 mark] . The number 5 can be written as 15 3 Shade two lozenges to indicate which of the following statements are true. [2 marks] A 15 and 3 are not integers B 15 and 3 are irrational numbers C 5 is an irrational number D 5 is a natural number E 5 is a rational number . Shade one lozenge to indicate which of the symbols below represents the set of rational numbers. [1 mark] 2 3 1 0 1 0 3 Do not write outside the box IB/G/Jun24/7516/2 0 2 . 1 Convert the bit pattern to hexadecimal. [1 mark] 0 2 . 2 Represent the decimal number 139 as an 8-bit unsigned binary integer. [1 mark] 0 2 . 3 Show how the unsigned binary number can be added to the unsigned binary number without converting the numbers into decimal. You must show all your working in binary. [2 marks] 0 0 1 0 0 0 1 1 + 0 0 1 0 1 0 1 1 Question 2 continues on the next page Turn over ► 4 Do not write outside the box IB/G/Jun24/7516/2 8 0 2 . 4 Show how the 8-bit two’s complement binary integer can be subtracted from the 8-bit two’s complement binary integer without converting the numbers to decimal. You must show all your working in binary. [2 marks] . The bit pattern in Figure 1 represents a 10-bit unsigned fixed point binary number with four bits before and six bits after the binary point. Figure 1 0 1 1 1 0 1 0 1 1 0 Convert the bit pattern in Figure 1 to decimal. [2 marks] 5 2 0 5 Do not write outside the box IB/G/Jun24/7516/2 0 3 . 1 State the name of the component on a sound card that transforms the continuous signal received from a microphone to a form that can be stored by a computer. [1 mark] 0 3 . 2 A bitmap image is 52 pixels in height and 26 pixels in width. The bitmap representation of the image requires 845 bytes. Calculate the maximum number of colours that could be used in the bitmap image. You should show all your working. [2 marks] 0 3 . 3 When a bitmap image is stored in a file, additional information is stored as well as the colours of the pixels. For example, the bitmap file might contain information on the date of creation, image width and height. State the name given to this additional information when storing a bitmap image. [1 mark] Question 3 continues on the next page Turn over ► 6 Do not write outside the box IB/G/Jun24/7516/2 0 3 . 4 A sound is recorded with a sample rate of 96 000 Hz and a sample resolution of 24 bits. The file size of the recording is 12 096 kilobytes. A sample rate of 1 Hz means that one sample has been taken every second. Calculate the duration of the sound recording. You should show all your working. [3 marks] 0 3 . 5 A sample resolution of 16 bits is commonly used in audio recordings. Explain why increasing the sample resolution from 16 bits to 24 bits can improve the quality of an audio recording. [1 mark] 7 Do not write outside the box IB/G/Jun24/7516/2 11 0 3 . 6 MIDI does not use sampling to represent music. Describe how music is represented using MIDI. [2 marks] 0 3 . 7 Explain one advantage of using MIDI instead of sampled sound to represent music. [1 mark] Turn over for the next question Turn over ► 8 Do not write outside the box IB/G/Jun24/7516/2 3 0 4 . 1 A message is encrypted using a Caesar cipher that operates with a shift value of four. For example, the letter A in plaintext would be represented by E in ciphertext. The ciphertext for the message is WSSDI. What is the plaintext for the message? [1 mark] 0 4 . 2 Explain two reasons why Caesar ciphers are vulnerable to being cracked. [2 marks] 9 Do not write outside the IB/G/Jun24/7516/2 1 3 . Shade one lozenge to indicate which of the following is an example of system software. A Computer game B Image editor C Programming language translator D Video conferencing software E Word processor Turn over for the next question [1 mark] box Turn over ► 5 0 0 5 . 2 An operating system manages hardware resources, for example the I/O devices associated with a computer system. State two other examples of hardware resources that an operating system is responsible for managing. [2 marks] 10 Do not write outside the box IB/G/Jun24/7516/2 2 0 6 . 1 Figure 2 shows the symbol for a logic gate. Figure 2 State the name of the logic gate shown in Figure 2. [1 mark] . Figure 3 shows a logic circuit. Figure 3 Complete the truth table for the logic circuit in Figure 3. [2 marks] A B C L M Z 0 0 0 0 0 1 0 1 0 0 1 1 1 0 0 1 0 1 1 1 0 1 1 1 6 0 11 Do not write outside the box IB/G/Jun24/7516/2 0 6 . 3 Figure 4 shows a logic circuit. Figure 4 Write a Boolean expression for Q. [3 marks] Question 6 continues on the next page Turn over ► 12 ite he IB/G/Jun24/7516/2 0 6 . 4 Do not wr outside t Using the rules of Boolean algebra, simplify the following expression. box W ⋅ X ⋅ Z + W ⋅ Z + X ⋅ Y ⋅ Z + W ⋅ X ⋅ Y ⋅ 1 You must show your working. [4 marks] Final answer______________________________________ 10 13 Do not write outside the box IB/G/Jun24/7516/2 0 7 . 1 Figure 5 shows some of the processor registers and buses that are used during the fetch stage of the fetch-execute cycle, together with the main memory. Figure 5 State the name of the components that are labelled in Figure 5 with the numbers 1 to 4. In the case of register names, the full names must be stated. [2 marks] 1 2 3 4 0 7 . 2 Describe the stored program concept. [2 marks] Question 7 continues on the next page Turn over ► 14 Do not write outside the box IB/G/Jun24/7516/2 8 0 7 . 3 In a particular processor instruction set, each instruction consists of an opcode and an operand. An operand could be an immediate value to be used by a program. State two other types of value that can be stored in an operand. [2 marks] 0 7 . 4 Computer A and Computer B both have a processor with a clock speed of 2.8 GHz but Computer A performs tasks much faster than Computer B. Computer A has a larger cache and greater word length than Computer B. Explain why the larger cache and greater word length are possible factors for the performance difference between Computer A and Computer B. [2 marks] Larger cache Greater word length 15 Do not write outside the box Turn over for the next question IB/G/Jun24/7516/2 DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED Turn over ► 16 Do not write outside the box Table 1 shows the standard AQA assembly language instruction set that IB/G/Jun24/7516/2 should be used to answer question Table 1 – standard AQA assembly language instruction set LDR Rd, <memory ref> Load the value stored in the memory location specified by <memory ref> into register d. STR Rd, <memory ref> Store the value that is in register d into the memory location specified by <memory ref>. ADD Rd, Rn, <operand2> Add the value specified in <operand2> to the value in register n and store the result in register d. SUB Rd, Rn, <operand2> Subtract the value specified by <operand2> from the value in register n and store the result in register d. MOV Rd, <operand2> Copy the value specified by <operand2> into register d. CMP Rn, <operand2> Compare the value stored in register n with the value specified by <operand2>. B <label> Always branch to the instruction at position <label> in the program. B<condition> <label> Branch to the instruction at position <label> if the last comparison met the criterion specified by <condition>. Possible values for <condition> and their meanings are: EQ: equal to NE: not equal to GT: greater than LT: less than AND Rd, Rn, <operand2> Perform a bitwise logical AND operation between the value in register n and the value specified by <operand2> and store the result in register d. ORR Rd, Rn, <operand2> Perform a bitwise logical OR operation between the value in register n and the value specified by <operand2> and store the result in register d. EOR Rd, Rn, <operand2> Perform a bitwise logical XOR (exclusive or) operation between the value in register n and the value specified by <operand2> and store the result in register d. MVN Rd, <operand2> Perform a bitwise logical NOT operation on the value specified by <operand2> and store the result in register d. LSL Rd, Rn, <operand2> Logically shift left the value stored in register n by the number of bits specified by <operand2> and store the result in register d. LSR Rd, Rn, <operand2> Logically shift right the value stored in register n by the number of bits specified by <operand2> and store the result in register d. HALT Stops the execution of the program. Labels: A label is placed in the code by writing an identifier followed by a colon (:). To refer to a label the identifier of the label is placed after the branch instruction. Interpretation of <operand2> <operand2> can be interpreted in two different ways, depending on whether the first character is a # or an R: 1. # – use the decimal value specified after the #, eg #25 means use the decimal value 25 2. Rm – use the value stored in register m, eg R6 means use the value stored in register 6 The available general purpose registers that the programmer can use are numbered 0–12 8 0 17 Do not write outside the box IB/G/Jun24/7516/2 0 8 Registers R1 and R3 each store a different positive number. Write a program using the standard AQA assembly language in Table 1 that will:  store the greater of these two numbers in R1  store 1 in R2 if the value originally in R1 is greater than the value in R3, storing 3 in R2 otherwise. [4 marks] Turn over for the next question Turn over ► 4 18 Do not write outside the box IB/G/Jun24/7516/2 5 0 9 . 1 RFID tags can be read by an RFID reader. Describe how data is read from an RFID tag. [3 marks] 0 9 . 2 An RFID tag can be active or passive. A passive tag must be moved within a few centimetres of an RFID reader to be read. An active tag will have its own power source, which allows it to be read from a greater distance. It is decided that RFID tags will be used in passports to store personal information. Explain why passive tags are likely to be a more appropriate choice than active tags for use in passports. [2 marks] 19 Do not write outside the box Turn over for the next question IB/G/Jun24/7516/2 DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED Turn over ► 20 Do not write outside the box IB/G/Jun24/7516/2 1 0 A smartphone company has designed a device that can be put into items such as luggage to help locate these items if they are lost. The device works by sending an encrypted signal containing its current location to nearby smartphones. The smartphones relay the signal to the company’s servers via the Internet, allowing a user to see the device’s exact location using a mobile phone app. The company expects to sell hundreds of millions of devices. The data collected from each device will be permanently kept in secondary storage on the company’s servers. The company is planning to use solid-state drives in the servers that will hold device location data but is unsure whether using solid-state drives is a good idea. Discuss a range of moral, ethical, legal and cultural issues raised by the new device and explain the properties of solid-state drives that the company should consider when deciding on a secondary storage technology. In your answer you will be assessed on your ability to follow a line of reasoning to produce a coherent, relevant and structured response. [12 marks] 21 Do not write outside the box IB/G/Jun24/7516/2 12 Turn over ► 22 Do not write outside the box IB/G/Jun24/7516/2 [2 marks] 1 1 . 2 A photographer wants to create a large file sharing network to allow thousands of photographers to share their photos w