Chapter 2 - Processor performance

Question 1

Clock speed

Answer 1

• system clock generates a series of signals, switching from 0 to 1 in order to synchronise CPU operations
• an operation starts on the rising edge (as the clock switches from 0 to 1)
• the greater the clock speed, the faster instructions will be executed, so a program takes less time to run

Question 2

Number of cores

Answer 2

• nowadays, dual core and even quad core processors are available
• theoretically, each core can perform its own FDE cycle, executing instructions twice or four times as fast, but some software is unable to make use of this feature

Question 3

Amount and type of cache memory

Answer 3

• A small amount of very fast and expensive memory inside the CPU - closer to CPU than RAM
• Stores frequently used instructions and data so that they don’t have to be fetched from main memory each time
• When it fills up, unused data and instructions are cleared to make space for the newer ones
• Levels of cache – small amount of extremely fast level 1 cache, medium amount of fairly fast level 2 cache, some CPUs have level 3 cache
• cache split into data cache and instruction cache (Harvard architecture)