4.7.3.7 Factors affecting processor performance Quiz: AQA Computer Science, Unit 7

The 20 questions

1. Which factor allows a processor to work on several parts of a workload at the same time?

   • A wider data bus
   • A faster clock speed
   • Multiple cores
   • A larger cache memory

2. How does cache memory improve processor performance?

   • It widens the address bus so that more memory locations can be addressed directly, which removes the need for main memory
   • It stores frequently used data and instructions close to the processor, reducing the time to access them
   • It stores the whole of secondary storage in very fast memory placed close to the processor, so that every file is always ready
   • It increases the number of cores that the processor is able to use at once, so more programs can be processed in parallel

3. How does a higher clock speed affect processor performance?

   • It has no effect on instructions, because the clock controls only the screen refresh rate
   • Fewer instructions are carried out each second, because the processor has less time per instruction
   • More clock cycles occur each second, so more instructions can be carried out each second if other factors allow
   • It increases the amount of main memory available to running programs

4. How does a longer word length affect processing?

   • Word length affects only secondary storage capacity and does not change processing
   • More bits are processed in each operation, so larger values can be handled in a single step
   • Fewer bits are processed in each operation, which saves power and time
   • Word length sets the clock speed of the processor directly, one bit per megahertz

5. How does the address bus width affect processor capability?

   • It determines the number of status flags that the processor can record for each result
   • It determines the number of cores that the processor is able to use at the same time
   • It determines the speed at which data is transferred over the data bus each second
   • It determines how many memory locations can be addressed directly, which limits the maximum main memory

6. How does the data bus width affect performance?

   • A wider data bus reduces the clock speed of the processor in order to keep the signals stable across all of the lines
   • A wider data bus removes the need for a cache in any processor design, because all data can be read at full speed
   • A wider data bus transfers more bits in each transfer, so a given amount of data needs fewer transfers
   • A wider data bus increases the number of memory locations that can be addressed directly, because more lines carry the addresses

7. A 64-bit value must be moved over a 16-bit data bus. How many transfers are needed?

   • 16
   • 8
   • 4
   • 2

8. How many distinct bytes can a processor with a 24-bit address bus address?

   • 24 MB, because the address bus width is measured in megabytes
   • 2^24 bytes, which is 16 MiB
   • 2^12 bytes, which is 4 KiB for any 24-bit bus
   • 2^48 bytes, which is 256 TiB for any 24-bit bus

9. A processor with 4 cores runs a single-threaded program. Which statement is most accurate?

   • The program runs four times faster because each core runs its own copy of it
   • The program can use only one core at a time, so the extra cores do not speed it up on their own
   • The extra cores add main memory that the program can use for its data
   • The program uses all four cores automatically, with no change to the software

10. Why might doubling the clock speed not double the performance of a processor?

    • The clock controls only the screen refresh rate of the display, so it has no effect on how fast the processing is done
    • Increasing the clock speed reduces the address bus width, so fewer memory locations are available to every program
    • Doubling the clock changes the word length of the processor, which halves the size of each instruction it can handle
    • Memory access times and other limits do not improve with the clock, so the processor may spend time waiting for data

11. Which factor most directly determines the number of bits the ALU handles in one operation?

    • The size of the cache memory
    • The number of cores in the processor
    • The width of the address bus
    • The word length of the processor

12. A processor has a 2 MB cache, and the program's working data is 8 MB. Which statement is most accurate?

    • Not all the data fits in the cache, so the processor sometimes has to fetch from main memory, which is slower
    • The cache is used only for instructions and never for the data that a program works on
    • All the data fits in the cache, because the cache always holds the whole of main memory
    • The cache is larger than secondary storage, so no fetching from any memory is ever needed

13. Which factor determines the total number of distinct memory locations that can be addressed?

    • The address bus width
    • The number of general-purpose registers
    • The data bus width
    • The clock speed

14. A processor has 8 cores, each running at 2 GHz. What is the maximum number of clock cycles it can complete per second across all cores?

    • 8 x 10^9, which counts the cores multiplied by a billion cycles
    • 2 x 10^9, which is the clock rate of a single core only
    • 1.6 x 10^10 (8 x 2 x 10^9)
    • 1.6 x 10^9, which divides the total cycles by ten for each core

15. Which statement about cache memory and main memory is correct?

    • Cache and main memory are identical in speed and size, and differ only in the price paid
    • Cache is slower and larger than main memory, and holds the operating system permanently
    • Cache holds data permanently, so main memory is not needed by the processor at all
    • Cache is faster but smaller than main memory, and holds copies of data that are used frequently

16. Which change would most improve the speed of a processor that spends much of its time waiting for memory?

    • A lower clock speed, so that the processor waits less time for each memory access
    • A shorter word length, so that each instruction takes up less space in memory
    • A larger or faster cache, which keeps frequently used data closer to the processor
    • A narrower data bus, which reduces the number of signals sent between components

17. A processor has a 64-bit word length. What is the maximum number of bits that a single ALU operation handles?

    • 32
    • 128
    • 8
    • 64

18. A 32-bit address bus can address 4 GB. Which change would double the addressable memory?

    • Doubling the number of cores in the processor
    • Doubling the clock speed of the processor
    • Doubling the number of general-purpose registers
    • Adding one address line, to make a 33-bit address bus

19. A computer runs many independent programs at once. Which combination would give the greatest improvement?

    • More cores, so that several programs can be processed in parallel
    • A shorter address bus, so that there are fewer memory locations to search
    • A narrower data bus, so that memory is accessed more often by each program
    • A lower clock speed, so that the processor runs cooler between programs

20. Which statement about clock speed as a measure of performance is most accurate?

    • It has no effect on processors that have a cache memory, whatever its size
    • It is the only factor that determines processor performance in every situation
    • It is measured in bytes per second and so has no direct link to processing cycles
    • It is one factor among several, and cycles per instruction and other factors also matter

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