9608_w15_qp_32
A paper of Computer Science, 9608
Questions:
6
Year:
2015
Paper:
3
Variant:
2
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1
In a particular computer system, real numbers are stored using floating-point representation with: • 8 bits for the mantissa, followed by • 4 bits for the exponent Two’s complement form is used for both mantissa and exponent. A real number is stored as the following 12-bit binary pattern: Calculate the denary value of this number. Show your working. Give the normalised binary pattern for +3.5. Show your working. Give the normalised binary pattern for –3.5. Show your working. The number of bits available to represent a real number is increased to 16. If the system were to use the extra 4 bits for the mantissa, state what the effect would be on the numbers that can be represented. If the system were to use the extra 4 bits for the exponent instead, state what the effect would be on the numbers that can be represented. A student enters the following expression into an interpreter: OUTPUT (0.1 + 0.2) The student is surprised to see the following output: 0.3000000000000001 Explain why this output has occurred.
3. Advanced Theory  →  3.1. Data representation
Open
2
In this question, you are shown pseudocode in place of a real high-level language. A compiler uses a keyword table and a symbol table. Part of the keyword table is shown below. • Tokens for keywords are shown in hexadecimal. • All the keyword tokens are in the range 00 to 5F. Keyword Token + = IF 4A THEN 4B ENDIF 4C ELSE 4D FOR 4E STEP 4F TO INPUT OUTPUT ENDFOR Entries in the symbol table are allocated tokens. These values start from 60 . Study the following piece of code: Start 0.1 // Output values in loop FOR Counter Start TO 10 OUTPUT Counter + Start ENDFOR Complete the symbol table below to show its contents after the lexical analysis stage. Symbol Token Value Type Start Variable 0.1 Constant Each cell below represents one byte of the output from the lexical analysis stage. Using the keyword table and your answer to part complete the output from the lexical analysis. The compilation process has a number of stages. The output of the lexical analysis stage forms the input to the next stage. Name this stage. State two tasks that occur at this stage. The final stage of compilation is optimisation. There are a number of reasons for performing optimisation. One reason is to produce code that minimises the amount of memory used. State another reason for the optimisation of code. What could a compiler do to optimise the following expression? A B + 2 * 6 These lines of code are to be compiled: X A + B Y A + B + C Following the syntax analysis stage, object code is generated. The equivalent code, in assembly language, is shown below: LDD 436 //loads value A ADD 437 //adds value B STO 612 //stores result in X LDD 436 //loads value A ADD 437 //adds value B ADD 438 //adds value C STO 613 //stores result in Y Rewrite the equivalent code, given above, following optimisation.
3. Advanced Theory  →  3.4. System software
1. Theory Fundamentals  →  1.4. Processor fundamentals
Open
3
Explain what is meant by circuit switching. There are many applications in which digital data are transferred across a network. Video conferencing is one of these. For this application, circuit switching is preferable to the use of packet switching. Explain why this is so. A web page is transferred from a web server to a home computer using the Internet. Explain how the web page is transferred using packet switching.
3. Advanced Theory  →  3.2. Communication and Internet technologies
Open
4
Four descriptions and four types of computer architecture are shown below. Draw a line to connect each description to the appropriate type of computer architecture. Description Computer architecture A computer that does not have the ability for parallel processing. SIMD The processor has several ALUs. Each ALU executes the same instruction but on different data. MISD There are several processors. Each processor executes different instructions drawn from a common pool. Each processor operates on different data drawn from a common pool. SISD There is only one processor executing one set of instructions on a single set of data. MIMD In a massively parallel computer explain what is meant by: Massive Parallel There are both hardware and software issues that have to be considered for parallel processing to succeed. Describe one hardware and one software issue. Hardware Software
3. Advanced Theory  →  3.3. Hardware
1. Theory Fundamentals  →  1.4. Processor fundamentals
Open
5
Complete the Boolean function that corresponds to the following truth table. INPUT OUTPUT P Q R Z Z = P . Q . R + The part to the right of the equals sign is known as the sum-of-products. For the truth table above complete the Karnaugh Map (K-map). PQ R The K-map can be used to simplify the function in part. Draw looparound appropriate groups of 1’s to produce an optimal sum-of-products. Using your answer to part , write the simplified sum-of-products Boolean function. Z = The truth table for a logic circuit with four inputs is given below: INPUT OUTPUT P Q R S Z Complete the K-map corresponding to the truth table above. PQ RS Draw looparound appropriate groups of 1’s to produce an optimal sum-of-products. Using your answer to part , write the simplified sum-of-products Boolean function. Z =
1. Theory Fundamentals  →  1.3. Hardware
3. Advanced Theory  →  3.3. Hardware
Open
6
A number of processes are being executed in a computer. A process can be in one of three states: running, ready or blocked. For each of the following, the process is moved from the first state to the second state. Describe the conditions that cause each of the following changes of state of a process: From blocked to ready From running to ready Explain why a process cannot move directly from the ready state to the blocked state. A process in the running state can change its state to something which is neither the ready state nor the blocked state. Name this state. Identify when a process would enter this state. Explain the role of the low-level scheduler in a multiprogramming operating system.
3. Advanced Theory  →  3.4. System software
1. Theory Fundamentals  →  1.4. Processor fundamentals
Open