Limits to ILP
Inherent lack of parallelism in programs
- Need to be able to execute (av. Depth of pipes) * (Nbr of units)
Complexity in hardware
- Needs large bandwidth for instruction fetch
- Requires large register bandwidth (multiported register files )
- Forwarding requires “long wires” (long wires are slow) as soon as there are may units
Difficulties specific to the implementation
- Superscalar in the issue logic
- VLIW in the compiler technology