Central Processing Unit (CPU)
12 Grade 10 Computer Studies questions on Central Processing Unit (CPU), with worked marking schemes. 12 questions are available on this topic in full.
Question 1
1 markA computer shop in Eldoret advertises a desktop whose processor runs at 3.2 GHz. What does this figure tell the buyer about the processor?
A. It can hold 3.2 gigabytes of data inside itself at any one time.
B. It can transfer 3.2 gigabytes of data to main memory in one second.
C. Its clock ticks about 3.2 million times every second.
D. It goes through about 3.2 billion clock cycles every second.
(1 mark)
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2 marksState two functions of the arithmetic and logic unit (ALU) of a computer.
(2 marks)
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3 marksExplain the function of each of the following parts of the CPU: memory address register (MAR); memory data register (MDR); accumulator.
(3 marks)
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1 markA laptop is advertised as having a quad-core processor. What does this mean?
A. It has four slots into which memory modules can be fitted.
B. It is able to open only four programs before it slows down.
C. It has four processing units on one chip, each able to execute instructions at the same time.
D. Its clock speed is four times that of an ordinary processor.
(1 mark)
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1 markWhile executing an instruction, the CPU can obtain a value it is working on most quickly from:
A. the hard disk.
B. the main memory (RAM).
C. a register inside the CPU.
D. the cache memory.
(1 mark)
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1 markWhich part of the CPU interprets a fetched instruction and sends out the signals that direct the other parts of the computer on what to do?
A. The arithmetic and logic unit.
B. The program counter.
C. The control unit.
D. The accumulator.
(1 mark)
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3 marksA processor is described as a 64-bit processor. Explain what this means and state one advantage it has over a 32-bit processor.
(3 marks)
Marking scheme
Award marks as follows: - 1 mark: the description refers to the word length of the processor, that is the number of bits it can handle in one operation. - 1 mark: a 64-bit processor handles 64 bits of data at a time, while a 32-bit processor handles 32 bits at a time. - 1 mark for any one advantage: it processes more data in each cycle, so work is completed faster; or it can address far more main memory, so the computer can run larger programs and bigger data files. Do not credit answers that simply say 64-bit is newer or better.
Question 8
2 marksDistinguish between the data bus and the control bus in a computer system.
(2 marks)
Marking scheme
1 mark for each correct description, and the distinction must be clear. - Data bus: carries the actual data and instructions being moved between the CPU, main memory and input/output devices; it is bidirectional (data moves both to and from the CPU). - Control bus: carries command and timing signals such as read, write, clock and interrupt signals that tell the other units when and what to do; it does not carry the data itself. Award full marks only where the candidate shows that one carries content and the other carries commands or timing.
Question 9
1 markWhile a program is running, what does the program counter hold?
A. The address of the next instruction to be fetched.
B. The two values that are about to be compared.
C. The actual instruction that is currently being decoded.
D. The result of the calculation that has just been completed.
(1 mark)
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1 markThe total number of memory locations that a CPU can address directly depends mainly on the:
A. width of the data bus.
B. speed of the system clock.
C. size of the cache memory.
D. width of the address bus.
(1 mark)
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3 marksOutline the three stages that the CPU goes through when carrying out a single instruction.
(3 marks)
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3 marksA cyber cafe in Nyeri replaces its computers with new ones that have a larger cache memory. Explain how the larger cache memory improves the performance of the computers.
(3 marks)
Marking scheme
1 mark for each creditable point, maximum 3. - Cache memory holds copies of the instructions and data that the CPU uses most frequently. - Cache is much faster to access than main memory (RAM) because it is inside or very close to the CPU. - With a larger cache, more of the needed instructions and data are found in the cache, so fewer slow fetches from RAM are needed. - The CPU therefore spends less time idle waiting for data and completes more work in the same time, so programs such as browsers respond faster for customers.
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