CPU Performance & FDE Cycle

CPU Performance & FDE Cycle

1. CPU performance

   • Clock speed= no. of FDE cycles per seconds (Hz per second), increasing clock speed= faster CPU running more instructions per second
   • Cache holds commonly used instructions/data, so they can be reached quicker and the CPU runs quicker. Increasing cache size means more instructions and data can be stored so the CPU runs even quicker
   • Cores= independent processors in CPU that process instructions. Doubling cores= double the number of instructions the cores can process

2. FDE cycle:1st step: Fetch

   • Value placed in Program Counter determines address of instruction to be carried out
   • Address passed to Memory Address Register to locate data/instruction
   • Value sent to memory to locate the address via address bus
   • Data in memory address sent to Memory Data Register via data bus

3. FDE cycle: Second step: Decode

   • CPU uses instruction set to decode (understand) the instruction
   • Instruction set= set of commands in language CPU understands

4. FDE cycle: Third step: Execute

   • Any actions required by the instruction take place, e.g. calculations
   • Arithmetic Logic Unit carries out calculations

5. Components

   • Program Counter- stores location of next instruction in program to be fetched
   • Memory Address Register- stores location for data to be fetched from/sent to memory
   • Memory Data Register- stores data that has been fetched from/will be sent to memory
   • Accumulator- stores result of calculation carried out by ALU
   • Current Instruction Register- stores instruction to be decoded by ALU
   • Arithmetic Logic Unit carries out arithmetic/logic operations in instruction
   • Control Unit- helps control the flow of data and decode instructions
   • RAM/Main Memory- volatile memory that stores data and programs currently in use (not permanent- power off= lost data)
   • Cache- small section of memory, stores commonly used data and instructions to increase processor speed

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