Instruction Level Parallelism (ILP) in SW or HW
• Loop level parallelism is easiest to see
• SW parallelism dependencies defined for program,
hazards if HW cannot resolve
• SW dependencies/compiler sophistication determine if
compiler can unroll loops
– Memory dependencies hardest to determine
• HW exploiting ILP
– Works when can’t know dependence at run time
– Code for one machine runs well on another
• Key idea of Scoreboard: Allow instructions behind stall
to proceed (Decode => Issue instr & read operands)
– Enables out-of-order execution => out-of-order completion
– ID stage checked both for structural & data dependencies