Please recall: architecture, ISA, microarchitecture
The architecture of a processor is defined as the instruction set architecture (ISA), i.e. everything that is seen outside of a processor.
In contrast, the microarchitecture comprises implementation techniques
- like number and type of pipeline stages, issue bandwidth, number of FUs, size and organization of on-chip cache memories etc.
- The maximum issue bandwidth and the internal structure of the processor can be changed.
- Even several architectural compatible processors may exist with different microarchitectures and all are able to execute the same code.
An optimizing compiler may also use the knowledge of the microarchitecture.