AQA AS COMPUTER SCIENCE Paper 2 FOR MAY 2023

AQA AS COMPUTER SCIENCE Paper 2 Monday 22 May 2023 Afternoon Time allowed: 1 hour 30 minutes Materials For this paper you must have: • a calculator. Instructions • 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. IB/G/Jun23/E13 7516/2 Answer all questions in the spaces provided. box . Shade in one lozenge to indicate which of the following values is an irrational number. [1 mark] A 3 4 B √2 C 73 D –19 . Shade in one lozenge to indicate which of the following values is a natural number. [1 mark] A 3 4 B √2 C 73 D –19 . Define the set of real numbers. [1 mark] . Shade in one lozenge to indicate which of the following symbols represents the set of numbers most suitable for counting the number of people in a room. box [1 mark] A ℕ B ℚ C ℝ D ℤ . What is meant by the term ordinal number? [1 mark] Turn over for the next question Turn over ► . Assembly language programmers can use hexadecimal to represent bit patterns instead of binary. Explain why assembly language programmers will often choose to use hexadecimal in preference to binary. box [1 mark] . How many different values can be represented using 10 bits? [1 mark] . Shade in one lozenge to indicate which of the following prefixes represents 106 [1 mark] A kibi B mebi C gibi D kilo E mega F giga Question 3 continues on the next page box Turn over ► . Table 1 shows two unsigned binary integers, Number 1 and Number 2. Complete the table to show the result in binary of adding the two numbers. You must complete the carry row to show the carry from the previous column where there is one. Table 1 Number 1 0 0 0 1 1 0 1 1 Number 2 0 0 0 0 0 1 1 1 Result Carry [1 mark] box . What is the result of subtracting the two’s complement binary number from the two’s complement binary number ? You should give your answer in two’s complement binary. You must show all your working in binary. [2 marks] . In decimal, what are the lowest and highest values that can be represented by an 8-bit two’s complement binary integer? [1 mark] Lowest: Highest: . What is the decimal equivalent of the bit pattern shown in Figure 1 if it represents an unsigned fixed-point binary value with two bits before the binary point and six bits after the binary point? box Figure 1 1 1 0 1 1 1 0 1 [2 marks] Turn over for the next question *07* Turn over ► Majority voting and the use of parity bits are two different systems that can be used to detect errors in the transmission of data. box . Explain why it is better for a majority voting system to send each bit five times instead of four. [1 mark] . Give two reasons why using a parity bit system might be preferred to using majority voting when transmitting data. [2 marks] . Figure 2 shows a bit pattern that a computer has received. Each byte contains a 7-bit ASCII code with a parity bit. The method used when transmitting data was odd parity, with the parity bit being transmitted in the leftmost bit of each byte. Clearly circle the byte of data which the system calculates has been received incorrectly. Spaces have been inserted between each byte for clarity. Figure 2 0 1 0 1 0 0 1 0 0 1 0 0 0 0 0 1 1 1 0 0 1 1 0 1 [1 mark] Turn over for the next question DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED box Turn over ► . Describe how to calculate the minimum storage requirements, excluding metadata, of a bitmapped image. box [1 mark] One way of representing sound digitally is by using sampling. . What is meant by the term sampling rate? [1 mark] . What is meant by the term sample resolution? [1 mark] . A sampled sound could be compressed using lossy compression. Describe a problem that may occur if lossy compression is used and how the compression method has caused this. box [2 marks] . An alternative to using sampled sound is MIDI. State two advantages of using MIDI instead of sampled sound. [2 marks] Turn over for the next question Turn over ► . Libraries are a type of system software. Describe what libraries are and why programmers use them. [2 marks] box