(a) What is the denary equivalent of the hexadecimal number A7?

Transcription

1 1 What is the denary equivalent of the hexadecimal number A7? You may use the space below for rough working. You may get some marks for your working, even if your answer is incorrect. Represent the denary value as an unsigned binary fixed point number, with 4 bits before and 4 bits after the binary point. Use the space below for rough working. (c) Represent the denary value -18 as an 8-bit two's complement binary integer. Use the space below for rough working. (d) What is the largest positive denary value that can be represented using 8-bit two's complement binary? Use the space below for rough working. Page 1 of 16

2 (e) Describe how 8-bit two's complement binary can be used to subtract one number from another number. In your answer you must show how the calculation would be completed using the method that you have described. You may use the space below for rough working. (4) Figure 1 shows a state transition diagram for a finite state machine (FSM). Table 1 shows the outputs produced by the finite state machine in Figure 1 for some possible input strings. Some of the outputs are missing from the table below. Input strings are processed starting with the right-most bit. Figure 1 Table 1 Input string Output string (f) (g) What output string should be in position in the table? What output string should be in position in the table? (h) What is the purpose of the finite state machine shown in Figure 1? (i) A finite state machine can be represented as a state transition diagram or as a state transition table. Table 2 is an incomplete state transition table for Figure 1. Page 2 of 16

3 Complete the unshaded cells in the table below. Table 2 Input Original state Output New state 0 S0 0 S0 1 1 S1 0 S1 S1 (3) (Total 17 marks) 2 The ASCII system uses 7 bits to represent a character. The ASCII code for the character A is 65; other alphabetic characters follow on from this in sequence. How many different characters can be represented using ASCII? How would the charater 'B' be represented in ASCII using 7 bits? Use the space below for rough working. Answer... (c) Characters are transmitted using an 8-bit code that includes a parity bit in the most significant bit. Using even parity, what bit pattern is sent for the character A? Use the space below for rough working. Answer... Page 3 of 16

4 (d) Explain how the even parity system works. Include a description of the roles of the sender and receiver during transmission. (4) (Total 8 marks) 3 The diagram below shows how some of the components of a computer system can be connected together. Page 4 of 16

5 The table below lists the names of six components in the column headings and the five letters (A-E) from the diagram in the row headings. For each row in the table, shade one lozenge, in the appropriate column, to indicate which component in the diagram has been labelled with the row letter. As an example, the first row has been completed for you, to indicate that component A in the diagram is the Address bus. Processor Address bus Data bus Main memory Keyboard Visual display unit A B C D E (Total 4 marks) 4 Explain the difference between application software and system software. Utility programs are one type of system software. Name two other types of system software (Total 4 marks) Page 5 of 16

6 5 An ICT technician at a secondary school has access to a variety of programs that she uses to manage a group of servers. State one use for each of the protocols listed below. (i) Telnet:... (ii) FTP:... (iii) POP3:... Whilst remotely connecting to one of the servers the technician executes a command that displays the current network connections. The table below shows these network connections. Active Internet Connections Proto Recv Q Send Q Local Address Foreign Address (state) tcp : :58539 ESTABLISHED tcp : :57458 ESTABLISHED tcp : :57459 CLOSE_WAIT From the table above provide an example of the following: (i) IP address:... (ii) Port:... (iii) Socket:... (c) State two reasons why the technician uses remote management software from her computer rather than going to the actual servers. Reason 1:... Reason 2:... (Total 8 marks) Page 6 of 16

7 6 The diagram below shows the state transition diagram of a finite state machine (FSM) used to control a vending machine. The vending machine dispenses a drink when a customer has inserted exactly 50 pence. A transaction is cancelled and coins returned to the customer if more than 50 pence is inserted or the reject button (R) is pressed. The vending machine accepts 10, 20 and 50 pence coins. Only one type of drink is available. The only acceptable inputs for the FSM are 10, 20, 50 and R. An FSM can be represented as a state transition diagram or as a state transition table. The table below is an incomplete state transition table for part of the diagram above. Complete the missing sections of the four rows of the table below. Original state Input New state S0 10 S10 S0 S0 S0 (3) Page 7 of 16

8 There are different ways that a customer can provide exactly three inputs that will result in the vending machine dispensing a drink. Three possible permutations are 20, 10, 20, 10, R, 50 and 10, 50, 50. List four other possible permutations of exactly three inputs that will be accepted by the FSM shown in the diagram above. (4) (Total 7 marks) 7 A systems analyst is planning a system for the administration of student courses to be used in an office in a college. The system must allow users at ten workstations to access and update a central database. The analyst initially plans to use either a peer-to-peer or a server-based network. Explain why a server-based network is likely to be more appropriate than a peer-to-peer network in this situation. Page 8 of 16

9 After considering other alternatives, the analyst finally decides to use a thin-client network. Explain how a thin-client network works and how the use of a thin-client network instead of a traditional rich-client (thick-client) network will affect the selection of the hardware to be used by the system. In your answer you will be assessed on your ability to use good English, and to organise your answer clearly in complete sentences, using specialist vocabulary where appropriate. (4) (c) The system will be networked within the college. This network will then be connected to the Internet so that staff who are out of the college can log in and access the system. This connection will use a gateway. What is the purpose of the gateway? (Total 7 marks) Page 9 of 16

10 8 A machine code instruction can be split into an opcode part and an operand part. (i) What does an opcode represent? (ii) What does an operand represent? State two advantages of writing a program in assembly language over writing a program in machine code. Advantage 1:... Advantage 2:... (Total 4 marks) Page 10 of 16

11 9 State the names of the logic gates represented by each of the three truth tables below. Input A Input B Output Logic gate name Input A Input B Output Logic gate name Input A Input B Output Logic gate name (3) Simplify the following Boolean expressions. (i) B. (A+ ) (ii) A. B + B Page 11 of 16

12 (iii) (c) Draw a logic circuit for the following Boolean expression: Q = (A B). B You will need to make use of the symbols below when drawing your logic circuit. (Total 9 marks) Page 12 of 16

13 10 Explain the differences between the World Wide Web and the Internet. (4) Major parts of the Internet run on a packet switched network. What is meant by the term packet switching? (c) A packet being sent across the Internet may contain the details of a socket, for example :80. Complete the table below to explain what each part of the socket in the table represents. Part Represents (Total 8 marks) Page 13 of 16

14 11 A pseudo-code representation of an algorithm is given below. FOR x 0 TO 7 DO IF (x MOD 16 >= 4) AND (x MOD 16 <= 11) THEN c 1 ELSE c 0 ENDIF IF (x MOD 8 >= 2) AND (x MOD 8 <= 5) THEN b 1 ELSE b 0 ENDIF IF (x MOD 4 = 0) OR (x MOD 4 = 3) THEN a 0 ELSE a 1 ENDIF OUTPUT (c, b, a) ENDFOR The MOD operator calculates the remainder resulting from an integer division. For example, 7 MOD 5 = 2, 14 MOD 5 = 4. The statement OUTPUT (c, b, a) will display the contents of the variable c, followed by the contents of the variable b and then the contents of the variable a. Explain what is meant by an algorithm. The decision table shown in Table 1 represents the logic of the second selection structure in the algorithm above. The decision table is only partially complete; the shaded cells that should show the actions to be taken have not been filled in. Table 1 Conditions x MOD 8 >= 2 False True True x MOD 8 <= 5 True False True Action b 1 b 0 Complete Table 1 so that it shows the actions to be taken when the conditions have particular values: an 'X' symbol should be placed in the relevant shaded cells to indicate the action that will be executed for the given conditions. Some of the shaded cells will need to be left empty. Page 14 of 16

15 (c) Dry run the algorithm above by completing Table 2. The first row has been completed for you. Table 2 x c b a Printed output (d) Explain, precisely, the purpose of the algorithm above. (5) (Total 10 marks) Page 15 of 16

16 12 The table below lists three situations which involve the transmission of data / information / addresses. For each row in the table below, place a tick in one column to indicate whether the transmission is most likely to be serial, most likely to be parallel or could be either serial or parallel. Situation Most likely to be Parallel Most likely to be Serial Could be either Serial or Parallel Sending data to a peripheral, such as a printer, that is plugged directly into a computer. Transferring memory addresses between the processor and the main memory of a desktop computer. Transmitting an across a WAN from a computer in England to an server in Scotland. (3) Data communication often uses a handshaking protocol. Explain one purpose of a handshaking protocol. (c) When data is transmitted over long distances, eg via satellites, latency can become a problem. Explain what latency is. (Total 5 marks) Page 16 of 16