9608_s20_qp_31 - revisedeck

9608_s20_qp_31

A paper of Computer Science, 9608

Questions:

9

Year:

2020

Paper:

3

Variant:

1

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1

In a particular computer system, real numbers are stored using floating-point representation with: • 10 bits for the mantissa • 6 bits for the exponent • two’s complement form for both mantissa and exponent. Calculate the normalised floating-point representation of +192.5 in this system. Show your working. Mantissa Exponent Working Calculate the normalised floating-point representation of –192.5 in this system. Show your working. Mantissa Exponent Working The floating-point representation has changed. There are now 12 bits for the mantissa and 4 bits for the exponent as shown. Mantissa Exponent Explain why +192.5 cannot be accurately represented in this format.

3. Advanced Theory → 3.1. Data representation

Open

2

The diagram shows four files and three methods of file organisation. Draw one line to match each file with its most appropriate method of file organisation. File File organisation Text file File for recording the temperature every hour Master file for paying each employee every month Customer user name and password file Sequential Random Serial

3. Advanced Theory → 3.1. Data representation

Open

3

A mobile phone company uses circuit switching for voice calls and packet switching to send and receive other data. Describe circuit switching. Explain why the company uses circuit switching for voice calls. Describe packet switching. Explain why the company uses packet switching to send and receive other data.

3. Advanced Theory → 3.2. Communication and Internet technologies

Open

4

Write the Boolean algebraic expressions for the following logic circuit. P Q Y X R X = Y = The logic circuit given in part is a full adder. Give the purpose of outputs X and Y in this circuit. X Y Give the use of the input R in this circuit.

3. Advanced Theory → 3.3. Hardware

1. Theory Fundamentals → 1.3. Hardware

Open

5

Complete these three statements about computer processors. A processor with a few simple fixed-length instructions that have a small number of instruction formats is called a processor. A processor with many complex variable-length instructions that has many instruction formats is called a processor. Instruction-level parallelism, applied to the execution of instructions during the fetch-execute cycle, is called .

1. Theory Fundamentals → 1.4. Processor fundamentals

Open

6

Duraid writes a short program in a high-level programming language. An interpreter executes the program. The following is part of Duraid’s program. DECLARE P, Q, R, X, Y : INTEGER CONSTANT M = 10 P = 4 Q = 2 R = 1 X = (P + Q) * (P – Q) Y = (M / Q) * (P + Q - R) Write the Reverse Polish Notation (RPN) for the following expression from Duraid’s program. (P + Q) * (P – Q) The interpreter is executing Duraid’s program. The expressions are in infix form. The interpreter converts the infix to RPN. The RPN expression for Y is: M Q / P Q + R − * The interpreter evaluates this RPN expression using a stack. Show the changing contents of the stack, as the interpreter evaluates the expression for Y. Use the values of the variables and constant given in the program. The first entry has been done for you. Convert the following RPN expression back to its infix form. P Q + M * R P − − Explain how RPN is used by an interpreter to evaluate expressions.

3. Advanced Theory → 3.4. System software

2. Fundamental Problem-solving and Programming Skills → 2.3. Programming

Open

7

A computer at a remote weather station is performing three tasks: • measuring and recording the temperature every 10 seconds • measuring and recording the wind speed every 10 seconds • sending the previous day’s temperature and wind speed readings to a scientist at another location via the Internet. The operating system is managing the multitasking of these tasks. At one point in time: • the temperature measuring and recording task is idle • the wind speed is being recorded • the task to send the previous day’s temperature and wind speed readings is waiting for an internet connection. Identify the process state for each task. Give a reason why each task is in that process state. Temperature measuring and recording process state Reason Wind speed measuring and recording process state Reason Sending process state Reason The weather station computer uses an operating system. Explain how this operating system uses interrupts to schedule the measuring and recording tasks.

3. Advanced Theory → 3.4. System software

1. Theory Fundamentals → 1.4. Processor fundamentals

Open

8

Martha wants to send a private message to Joshua over the Internet. Martha and Joshua’s computers have already exchanged digital certificates. Identify three items that could be contained in a digital certificate. Joshua and Martha’s digital certificates are used to ensure that Martha’s message has not been altered during transmission. Explain how asymmetric encryption uses the contents of the digital certificates to ensure that the message has not been altered during transmission.

3. Advanced Theory → 3.5. Security

Open

9

A train cannot move if any of the eight automatic train doors are open. The train door monitoring system, set out below, checks that all the doors are closed before the train can move. • If a monitoring system detects that a door is open, it sets a specific bit in address 500 to 1. • If the bit for door one is equal to 1, the binary value for hexadecimal FF is sent to address 501. The contents of address 501 are changed to make door 1’s light flash when the door is open. • If the bit for door two is equal to 1, the binary value for hexadecimal FF is sent to address 502. The contents of address 502 are changed to make door 2’s light flash when the door is open. This is repeated for each door from 3 to 8. • Each door sets its bit in address 500 to zero when the door closes, and the contents of the corresponding door address are set to zero. • The train manager can identify which door is open from the flashing light. The current contents of address 500 are: Door number Address 500 Complete the following table by writing the values stored in addresses 503 to 508. Use the contents of address 500 shown above. Note that addresses 501 and 502 are complete. Door 1 Door 2 Door 3 Door 4 Door 5 Door 6 Door 7 Door 8 The following table shows assembly language instructions for the processor controlling the train door monitoring system that has one general purpose register, the Accumulator (ACC). Instruction Explanation Label Op code Operand LDM &n Load the hexadecimal number n to ACC LDD Load the contents of the location at the given address to ACC STO Store the contents of ACC at the given address AND &n Bitwise AND the contents of ACC with the hexadecimal number n CMP &n Compare the contents of ACC with the hexadecimal number n JPE Following a compare instruction, jump to or if the compare was True : Labels an instruction WAIT Macro to wait one second before the next instruction is executed After rechecking the doors, address 500 now contains 10101010. Complete the table by writing the values of the Accumulator (ACC) and the contents of address 501 as these instructions are executed once to check door 1. Instruction ACC Label Op code Operand CHECK1: LDD AND &80 CMP &00 JPE DOOR1 LDM &FF DOOR1: STO WAIT LDM &00 STO WAIT JMP CHECK1 Write the assembly language instructions to check door 2. Instruction Label Op code Operand Explain how the check door routines show a flashing light or no light.

1. Theory Fundamentals → 1.4. Processor fundamentals

3. Advanced Theory → 3.6. Monitoring and control systems

1. Theory Fundamentals → 1.1. Information representation

Open