4. Further Problem-solving and Programming Skills
A section of Computer Science, 9608
Listing 8 of 8 questions
A museum stores antique items that need to be kept at constant temperature. The museum is not sure about the actual temperatures. The museum installs some equipment. This records the temperatures every hour and ensures the temperature stays within a set range. Identify the type of system described. The system has a temperature sensor. Identify two other items of hardware that the museum can use for the type of system identified. Describe the purpose of each item. Item 1 Purpose Item 2 Purpose The equipment records the temperature in all seven rooms in the museum. Each recording is stored as two successive bytes in memory. The format is as shown. Temperature Room Byte 1 Byte 2 The room is indicated by the setting of one of the bits in Byte 2 to 1. For example, room 7 is indicated by setting bit 7 to 1. Bit 0 of Byte 2 is a flag: • The flag’s initial value is zero. • When the reading has been processed, the flag’s value is set to 1. Byte 1 contains the temperature reading as an unsigned integer. One reading returns the following binary data. Temperature Room Byte 1 Byte 2 Analyse the data contained in the two bytes. The system receives a temperature reading of 238 from room number 4. Complete the bytes to show the two bytes for this recording. The reading has not yet been processed. Byte 1 Byte 2
9608_s18_qp_31
THEORY
2018
Paper 3, Variant 1
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A museum stores antique items that need to be kept at constant temperature. The museum is not sure about the actual temperatures. The museum installs some equipment. This records the temperatures every hour and ensures the temperature stays within a set range. Identify the type of system described. The system has a temperature sensor. Identify two other items of hardware that the museum can use for the type of system identified. Describe the purpose of each item. Item 1 Purpose Item 2 Purpose The equipment records the temperature in all seven rooms in the museum. Each recording is stored as two successive bytes in memory. The format is as shown. Temperature Room Byte 1 Byte 2 The room is indicated by the setting of one of the bits in Byte 2 to 1. For example, room 7 is indicated by setting bit 7 to 1. Bit 0 of Byte 2 is a flag: • The flag’s initial value is zero. • When the reading has been processed, the flag’s value is set to 1. Byte 1 contains the temperature reading as an unsigned integer. One reading returns the following binary data. Temperature Room Byte 1 Byte 2 Analyse the data contained in the two bytes. The system receives a temperature reading of 238 from room number 4. Complete the bytes to show the two bytes for this recording. The reading has not yet been processed. Byte 1 Byte 2
9608_s18_qp_33
THEORY
2018
Paper 3, Variant 3
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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.
9608_s17_qp_31
THEORY
2017
Paper 3, Variant 1
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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.
9608_s17_qp_33
THEORY
2017
Paper 3, Variant 3
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Data types can be defined in a programming language. The data type, StudentRecord, is defined by the code: TYPE StudentRecord DECLARE StudentID : INTEGER DECLARE StudentFirstName : STRING DECLARE StudentSurname : STRING DECLARE StudentDOB : DATE DECLARE StudentCourse : ARRAY[1:10] OF STRING ENDTYPE A variable, CollegeStudent, is declared with the code: DECLARE CollegeStudent : StudentRecord Write a pseudocode statement to assign 6539 to the StudentID of CollegeStudent. The type definition for StudentRecord is changed. Students can take six courses from: Computer Science, Engineering, Science, Maths, Physics, Chemistry, Music, Drama and English Language. Rewrite one line from the type definition of StudentRecord to implement the change. DECLARE The values for the field StudentID must be between 1 and 8000 inclusive. Rewrite one line from the type definition of StudentRecord to implement the change. DECLARE A programmer is asked to write a program to process the assessment data for each student. Students sit one exam in every course they take. A composite data type, StudentAssessment, needs to be defined with the following three fields. • a student assessment code (a unique code of three letters and two digits) • the marks for the six exams • the average mark of the six exams Write pseudocode to define the data type StudentAssessment. Data about all students and their assessments are stored in a file that uses random organisation. The StudentID is used as the key field. The program allows a user to enter data for a new student. Explain how the program adds the new data to the file.
9608_s18_qp_32
THEORY
2018
Paper 3, Variant 2
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Five modes of addressing and five descriptions are shown below. Draw a line to connect each mode of addressing to its correct description. Mode of addressing Description direct the operand is the address of the address of the value to be used immediate the operand is the address of the value to be used indexed the operand is the offset from the current address where the value to be used is stored indirect the operand plus the contents of the index register is the address of the value to be used relative the operand is the value to be used
9608_s15_qp_11
THEORY
2015
Paper 1, Variant 1
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Five modes of addressing and five descriptions are shown below. Draw a line to connect each mode of addressing to its correct description. Mode of addressing Description direct the operand is the address of the address of the value to be used immediate the operand is the address of the value to be used indexed the operand is the offset from the current address where the value to be used is stored indirect the operand plus the contents of the index register is the address of the value to be used relative the operand is the value to be used
9608_s15_qp_12
THEORY
2015
Paper 1, Variant 2
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When an application program requests a file stored on a hard disk, the computer system reads the file. Use the statement labels A to H to complete the sequence of steps that describe how this happens. Label Statement A When the hard disk drive has read the file, it generates an interrupt. B While the file continues, the head reads successive clusters of sectors from the disk and writes data into the disk buffer. C The head reads the first cluster of sectors from disk and writes data into the disk buffer. D The head moves to the correct track. E The operating system transfers the contents of the disk buffer to the application program’s data memory. F In the relevant directory file, the operating system looks up the track and sector where the file begins. G Application program passes file read request to the operating system. H The hard disk drive waits for the correct sector to arrive under the head. 1. The application program executes a statement to read a file. 2. 3. The operating system begins to spin the hard disk, if it is not currently spinning. 4. 5. 6. 7. 8. 9. 10.
9608_w16_qp_12
THEORY
2016
Paper 1, Variant 2
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Questions Discovered
8