9608_s17_qp_31
A paper of Computer Science, 9608
Questions:
6
Year:
2017
Paper:
3
Variant:
1
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1
Consider the following user-defined data type: TYPE LibraryBookRecord DECLARE ISBN : INTEGER DECLARE Title : STRING ENDTYPE Write a pseudocode statement to declare a variable, Book, of type LibraryBookRecord. Write a pseudocode statement that assigns ‘Dune’ to the Title of Book. The user-defined data type LibraryBookRecord needs to be modified by adding the following fields: • a field called Genre which can take two values, fiction or non-fiction • a field called NumberOfLoans which can be an integer value in the range 1 to 99 Write the updated version of LibraryBookRecord. A pointer is a variable that stores the address of a variable of a particular type. Consider the code on page 3, which uses the following identifiers: Identifier Data type Description IntPointer ^INTEGER pointer to an integer IntVar INTEGER an integer variable Temp1 INTEGER an integer variable Temp2 INTEGER an integer variable IntVar // assigns the value 57 to the integer // variable IntVar IntPointer @IntVar // assigns to IntPointer the address of the // integer variable IntVar Temp2 IntPointer^ // assigns to variable Temp2 the value at an // address pointed at by IntPointer IntPointer^ Temp1 // assigns the value in the variable Temp1 to // the memory location pointed at by IntPointer The four assignment statements are executed. The diagram shows the memory contents after execution. Variable Memory address Contents . . . IntVar . . . IntPointer . . . Temp1 Temp2 . . . Use the diagram to state the current values of the following expressions: @Temp2 IntPointer IntPointer^ IntPointer^ = Temp2 + 6 Write pseudocode statements that will achieve the following: Assign the value 22 to the variable Temp2. Place the address of Temp1 in IntPointer. Copy the value in Temp2 into the memory location currently pointed at by IntPointer.
2. Fundamental Problem-solving and Programming Skills  →  2.3. Programming
2. Fundamental Problem-solving and Programming Skills  →  2.2. Data representation
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2
The following incomplete table shows descriptions and terms relating to malware. Complete the table with appropriate description and terms. Description Term A standalone piece of malicious software that can replicate itself using a network. Use email to attempt to obtain an individual’s confidential data. Virus State two vulnerabilities that the malware in part or part can exploit. Vulnerability 1 Vulnerability 2 Question 2 continues on the next page. Anna has to send an email to Bob containing confidential information. Bob and Anna have never sent emails to each other before. Bob and Anna both have public and private keys. The first step is for Anna to request that Bob sends her one of his keys. State the key that Bob sends. Explain how Anna can be sure that it is Bob who has sent the key. Anna has received the key from Bob. The following incomplete table shows the sequence of actions between Anna and Bob to communicate the confidential information. Complete the table. The person performing the action What that person does Anna Requests Bob’s key. Bob Anna Anna Sends the email to Bob. Bob
3. Advanced Theory  →  3.5. Security
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3
Consider the following logic circuit, which contains a redundant logic gate. A B X C Write the Boolean algebraic expression corresponding to this logic circuit. X = Complete the truth table for this logic circuit. A B C Working space X Complete the Karnaugh Map (K-map) for the truth table in part . AB C The K-map can be used to simplify the expression in part . Draw looparound appropriate groups to produce an optimal sum-of-products. Write a simplified sum-of-products expression, using your answer to part . X = One Boolean identity is: A + ̅A.B = A + B Simplify the expression for X in part to the expression for X in part . You should use the given identity.
3. Advanced Theory  →  3.3. Hardware
1. Theory Fundamentals  →  1.3. Hardware
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4
A bank has 95 000 customers. Each customer has a unique ID. When a customer uses an Automated Teller Machine (ATM) to obtain cash, their current balance is checked. The balance is stored in a file which has the following fields: • the customer ID (6-digit number in the range 100000 to 999999) • an encrypted PIN • the current balance The file can store a maximum of 100 000 records. Give a reason why a random organisation would be appropriate for this file. An algorithm for inserting a new record in this file uses the following hash function: RecordKey CustomerID MOD 100000 where RecordKey is the record position in the file. Complete the table to show the values generated by the hash function for the given customer IDs. CustomerID RecordKey State the range of possible values for RecordKey. Minimum value of RecordKey: Maximum value of RecordKey: A procedure is written to insert a new record into the file. Complete the algorithm for this procedure. PROCEDURE InsertRecord(CustomerID : INTEGER) RecordKey CustomerID MOD 100000 Success FALSE // Find position for new record and insert it REPEAT IF record at position RecordKey is ……………………… THEN Insert new record at position RecordKey Success TRUE ELSE IF RecordKey = ……………………… THEN RecordKey ……………………… ELSE RecordKey ……………………… + 1 ENDIF ENDIF UNTIL Success = TRUE ENDPROCEDURE Explain why an encrypted version of the PIN is stored in the file. A customer attempts to withdraw cash from an ATM. An algorithm is used to check if the customer has entered the correct PIN. Complete the algorithm. 1. Customer ID is read from card. 2. Customer enters PIN. 3. Customer PIN is 4. 5. Customer record is located in file. 6. 7. If match then transaction can proceed.
4. Further Problem-solving and Programming Skills  →  4.1. Computational thinking and problem-solving
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5
A web browser is used to request and display a page stored on an internet web server. Explain how each of the following items is used in this event. Packet: Router: TCP/IP: The Internet can be used for video conferencing. Data can be transmitted over the Internet using either packet switching or circuit switching. State two problems that could arise if video conferencing were to use packet switching. Problem 1 Problem 2 Explain what is meant by circuit switching. Explain how the use of circuit switching overcomes the problems you have identified in part .
3. Advanced Theory  →  3.2. Communication and Internet technologies
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6
A computer system is used to manage some of the functions in a vehicle. The vehicle has a number of sensors and actuators. One sensor is used to monitor the moisture on the screen. If the moisture exceeds a pre-set value, the windscreen wiper motor turns on automatically. The software used in the computer system is dedicated to the sensor management functions. When the system starts, the software runs some initial tasks. It then loops continuously until the system is switched off. State the name given to the type of system described. Explain your answer to part . Within the software loop, the value of each sensor is read in turn. The value read from the sensor is then processed. State two drawbacks with this method of reading and processing sensor data. Drawback 1 Drawback 2 An alternative method of reading and processing sensor data is to use interrupts. Each sensor is connected so that it can send an interrupt signal to the processor if its value changes. On receipt of an interrupt signal, the processor carries out a number of steps as shown in the following diagram. Interrupt Return to task 1. Disable interrupts 6. Enable interrupts 2. Save current task 3. Identify source of 4. Jump to Interrupt Service Routine interrupt 5. Restore task State the purpose of step 1. State the purpose of step 6. Explain how the current task is saved in step 2. State two benefits of using interrupts to read and process the sensor data. Benefit 1 Benefit 2 The interrupt handler in step 3 has to test each bit of a 16-bit register to discover the source of the interrupt. The contents of the 16-bit register are loaded into the 16-bit accumulator: Accumulator Bit: An instruction is required to achieve the following: • If bit 9 is zero, set the accumulator to zero. • If bit 9 is one, set the accumulator to a non-zero value. Write this instruction using an appropriate bitwise operation.
3. Advanced Theory  →  3.4. System software
1. Theory Fundamentals  →  1.4. Processor fundamentals
3. Advanced Theory  →  3.3. Hardware
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