Chapter 4, Problem 4.12.5E

Program Plan Intro

Hazard:

• When a problem occurs at the instructional pipeline of the CPU it is called as hazard.
• When an instruction contains hazard, it may result with wrong computational answers during the execution of the instruction.
• There are three types of hazard namely structural, data and control.
• The two ways to deal with the hazard is removal and stall.
  • Removal is a process where the hardware or complexity is added to remove the hazards present.
    • By passing and forwarding.
    • Speculation.
  • When the performance is sacrificed to prevent the hazard that is going to happen is called as stalling.

Data dependency:

• Data dependency occurs when the data that is produced by another instruction is required to process another instruction.
• Data dependency is of three types they are:
  • RAW(Read After Write):
    • The instruction that is present later reads an operand before the instruction that is present at earlier instruction being read.
  • WAW(Write After Write):
    • The instruction that is present later writes to an operand before the instruction that is present at earlier instruction being written.
  • WAR(Write After Read):
    • The instruction that is present later writes to an operand before the instruction that is present at earlier instruction being read.