Preview

03 - Factors affecting CPU performance

 1. Read the following excerpt on 'Clock Speed'. Is it true or false?
The operating frequency of the CPU (also known as the CLOCK SPEED) determines how
fast it can process instructions.

The speed is measured in terms of Hertz, and it is usually lies in the megaHertz (MHz) 
or gigaHertz (GHz) range. A megaHertz means that the CPU can process one million 
instructions per second whereas a gigahertz CPU has the capability to process one 
billion instructions per second. In today's technology, all CPUs run in the gigahertz 
range and you seldom see CPUs with speed in the MHz range anymore.

Theoretically, a 500 MHz CPU is six times slower than a 3 GHz CPU and a 3.6 GHz CPU is
faster than a 3 GHz or a 3.4 GHz CPU. In general, the higher the frequency of a CPU, 
the faster the speed of the computer

  True

  False

 2. The performance of the CPU is directly related to the performance of your personal computer. There are four factors (The 4 Cs) to consider. Fill in the blanks.
The following are all factors that affect the performance of the CPU:

*Note: They are sometimes referred to as the 4 Cs

1.____ speed
2. number of processor _____
3. _____ size
4. ______ type.

  1. clock 2. cores 3. cache 4. cache

  1. coping tech 2. cores 3. cache 4. computer

  1. compartment 2. crux 3. cache 5. cache

  1. computer 2. cache 3. crumpet 4. compartment

 3. The following paragraph also describes Clock Speed. Can you fill in the blanks?
Every computer has a 'clock'. This is a crystal that vibrates, generating 'pulses' that are 
used to control how the different components of a computer system work together. 
If you have a 800Mhz machine, it means the system clock is generating approximately 
800 million pulses every second! 

The ________________________________, the more fetch-decode-execute cycles the CPU can 
perform in a second and (very broadly) the faster your programs should go! 
(There are lots of other factors that may mean this is not the case, however)
clockspeed.png

  the slower the clock

  the lighter the clock

  the faster the clock

  the heavier the clock

 4. The clock speed can be simply defined as:

  the speed at which the processor can execute instructions. The faster the clock, the more instructions can be processed.

  the speed at which a very tiny clock can travel to the printer and back in order to aid printing.

  the wires inside a tiny crystal called a CPU clock. The faster the vibration of the wires, the better the processing.

  the weight of the clock hands that tick around the CPU. The faster the hands, the quicker the processing of data.

 5. Two brains are better than one right? And four brains are even better. Multiple cores are a key factor in performance. Read the following paragraph and fill in the blanks.
 1. A CPU traditionally had one 'core' but processors these days might be dual-core or 
    quad-core for example. 
 
 2. A core is actually a processor with its own cache. 
 
 3. So a dual-core CPU has not one but two processors. 
 
 4. A quad core CPU has four processors
 
 5. Each 'brain' can be working on different parts of a program __________________
  and so this speeds up the overall CPU's performance.
quadcore.png

  one after the other

  at the same time

  carrying out each instruction four times

  waiting patiently for the other one to finish first

 6. Although CPUs fetch instructions from RAM, there is another place they can get instructions from, called _______.

  'cache'

  'cartesian fluid'

  'common ground'

  'computer source'

 7. Cache is like RAM but the one difference is that it is much ___________ to read and write from it rather than from RAM. This obviously speeds up CPU performance.

  slower

  lighter

  craftier

  faster

 8. Which of the following statements is true of CPU cache?
1. Cache will store the most used (most frequently used) instructions
2. It is a lot quicker for the CPU to get data from the cache than from RAM
3. The more cache a computer has, the better the CPU will perform
4. Cache is effectively a small and extremely fast memory
5. Cache isn't exactly cheap - for instance, Intel Core i7 Extreme Processor 
   comes with a 12MB L3 cache, which also explains its hefty price tag of approx. $1,000
6. The larger the cache size, the faster the data transfer and the better the CPU 
   performance

  All of these statements are true

  1 and 2 are true - the rest are false

  None of these statements are true

  1, 5 and 6 are true statements

 9. The less frequently certain data or instructions are accessed, the ____ down the cache level the data or instructions are written.

  lower

  wider

  narrower

  higher

 10. Another important characteristic of a processor is its word size. Read the interesting note below and see if you can define the term 'word size'.
Word size is a key factor when it comes to CPU performance.

The more bits the CPU can work with in one clock cycle, the 
faster the computer will go. 

The early commercial computers like the Spectrum ZX were 8-bit 
computers (in another words, the processor could work on 8 bits 
of data at a time). Things have moved on since the early 1980s 
and you are likely to be using either a 32-bit computer or a 
64-bit computer now.

|It's possible we will all be buying 128-bit computers in the 
very near future. 
wordsize.png

  This is the number of bits that the CPU can work with in any one clock cycle

  This is the number of words that a CPU can understand in any given language

  The is the number of words that a CPU can write to the RAM in one clock cycle

  There is no such thing as 'word size'

 11. A dual core processor may have twice the power but it does not always perform twice as fast. Is this true?

  Yes - but I'm not sure why

  Yes - because the software may not always be able to take full advantage of both processors

  No - double the cores and you will always have double the performance

  No - the performance will either double or triple with the dual core over single core

 12. It is possible for a computer with a slower processor but larger cache memory to be faster in system performance than computers with faster processors but limited cache.

  False

  True

 13. There are levels of cache. Level 1 is extremely fast but small (between 2 - 64KB). Some CPUs also have Level 3 cache. How would you define Level 2?

  Level 2 cache is exactly the same as Level 1 cache but stored externally

  Level 2 cache is the fastest type of cache and is larger in size than Level 1

  Level 2 cache is extremely slow but medium-sized (256KB - 2MB)

  Level 2 cache is fairly fast and medium-sized (256KB - 2MB)

 14. When an instruction is fetched from 'main memory' it is copied into the cache. Why?

  So that the cache can be enlarged as a large cache is generally a good thing

  So that the cache holds a copy of the instruction incase it is deleted elsewhere

  So that if it is needed again soon after, it can be fetched from the cache which is quicker than going back to main memory

  So that the cache is aware of the instruction being carried out and can store it until it has been processed

 15. True or False? All processor activities begin on a clock pulse, although some activities may take more than one clock cycle to complete.
Note: One clock cycle per second = 1 Hertz (hz)
Clock speed is measured in Gigahertz(GHz) - about 1 billion
cycles per second!

  False

  True