A-level COMPUTER SCIENCE Paper 2

A-level COMPUTER SCIENCE Paper 2 Time allowed: 2 hours 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 100. 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. Answer all questions. box . Describe how a 12-bit unsigned binary integer such as 110 can be converted directly into hexadecimal. The method you describe must not involve converting into decimal. [2 marks] . State one reason why hexadecimal is often used in preference to binary. [1 mark] . A data communications system uses parallel data transmission. Describe how parallel data transmission works. [2 marks] . State one advantage of serial data transmission over parallel data transmission. [1 mark] box . Shade one lozenge to indicate which of these statements about data communications systems is false. [1 mark] A For a particular communications channel, the bit rate can be higher than the baud rate. B Latency is the rate at which signals on a wire or line can change. C The bandwidth of a transmission medium is the range of signal frequencies that the medium can transmit without a significant reduction in signal strength. D The greater the bandwidth of a transmission medium the higher the bit rate that can be achieved by a communication system using it. . State the purpose of the start bit in asynchronous serial transmission. [1 mark] . State the purpose of the stop bit in asynchronous serial transmission.