9608_s18_qp_33
A paper of Computer Science, 9608
Questions:
7
Year:
2018
Paper:
3
Variant:
3
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1
In a computer system, real numbers are stored using normalised floating-point representation with: • 12 bits for the mantissa • 4 bits for the exponent • Two’s complement form for both mantissa and exponent. Find the denary value for the following binary floating-point number. Mantissa Exponent Show your working. Working Answer Calculate the normalised floating-point representation of 5.25 in this system. Show your working. Working Mantissa Exponent The size of the mantissa is decreased and the size of the exponent is increased. State how this affects the range and precision of the numbers that the computer system can represent.
3. Advanced Theory  →  3.1. Data representation
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3
Star and bus are two types of topology that can be used in a Local Area Network (LAN). Star topology Bus topology State one benefit and one drawback of the star topology. Benefit Drawback State one benefit and one drawback of the bus topology. Benefit Drawback The sequence of steps 1 to 7 describes what happens when the LAN transmits data from Computer X to Computer Y using circuit switching. Four statements (4 to 7) are missing from the sequence. A Computer X sends the data. B The sender signals node to deallocate resources. C Computer Y sends a receipt signal. D If available, Computer X sets up path between nodes. Write one letter (A to D) in the appropriate space to complete the sequence. Computer X sends a connection request to Computer Y. Computer Y sends ready or busy signal. If busy, Computer X waits and then resends the connection request to Computer Y. …………… …………… …………… …………… Protocols are essential for successful transmission of data over a network. The TCP/IP protocol suite operates on many layers. State the appropriate layer for each protocol in the following table. Protocol Layer TCP IP SMTP Peer-to-peer (P2P) file sharing uses the BitTorrent protocol. Explain how the BitTorrent protocol allows files to be shared.
3. Advanced Theory  →  3.2. Communication and Internet technologies
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4
A Boolean expression produces the following truth table. INPUT OUTPUT A B C X Write the Boolean expression for the truth table as a sum-of-products. X = Complete the Karnaugh Map (K-map) for the truth table in part . AB C The K-map can be used to simplify the function in part . Draw looparound appropriate groupof 1s to produce an optimal sum-of-products for the table in part . Write the simplified sum-of-products expression for your answer to part . X = A logic circuit with four inputs produces the following truth table. INPUT OUTPUT A B C D X Complete the K-map that corresponds to the truth table. AB CD Draw looparound appropriate groupof 1s to produce an optimal sum-of-products for the table in part . Write the simplified sum-of-products expression for your answer to part . X =
3. Advanced Theory  →  3.3. Hardware
1. Theory Fundamentals  →  1.3. Hardware
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5
The following syntax diagrams show the syntax of: • an assignment statement • a variable • a signed integer • a letter • a digit • an operator = + - letter digit operator signed integer variable assignment statement variable letter letter digit variable signed integer operator x y z ˄ \ The following assignment statements are invalid. Give the reason in each case. xy = xy ^ c4 Reason zy = zy \ 10 Reason yy := xz ^ − 6 Reason Complete the Backus-Naur Form (BNF) for the syntax diagrams on the opposite page. ::= ::= ::= ::= Rewrite the BNF rule for a variable so that it can be any number of letters. ::=
3. Advanced Theory  →  3.4. System software
2. Fundamental Problem-solving and Programming Skills  →  2.3. Programming
1. Theory Fundamentals  →  1.1. Information representation
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6
A company specialises in educational software. The company is concerned that malware might disrupt their business. Add appropriate descriptions and terms in the table. Description Term A Redirection to a bogus website that appears to be legitimate to gain confidential data. B Use email to attempt to gain a user’s confidential data. C Spyware D Worm A member of staff is using the Internet to carry out research. They are worried about the threat from terms A and B. Identify one solution to the each of the threats. Term A Term B A customer downloads a new educational software package from the company. Explain how the customer’s and the company’s computers use a hashing algorithm to assure the customer that: • the software has come from the company (is authentic) and • no one has altered it.
3. Advanced Theory  →  3.5. Security
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7
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
4. Further Problem-solving and Programming Skills  →  4.1. Computational thinking and problem-solving
3. Advanced Theory  →  3.6. Monitoring and control systems
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