Architecture and micro-architecture
Architecture does not tell you how a processor is built and actually works. The build and design of a processor is referred to as micro-architecture. Micro-architecture tells you how a particular processor works.
Micro-architecture includes things like:
- Pipeline length and layout.
- Number and sizes of caches.
- Cycle counts for individual instructions.
- Which optional features are implemented.
For example, Cortex-A53 and Cortex-A72 are both implementations of the Armv8-A architecture. This means that they have the same architecture, but they have very different micro-architectures, as shown in the following image:
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 |
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Target |
Optimized for power efficiency | Optimized for performance |
| Pipeline |
8 stages In-order |
15+ stages Out-of-order |
| Caches |
L1 I cache: 8KB - 64KB L1 D cache: 8KB - 64KB L2 cache: optional, up to 2MB |
L1 I cache: 48KB fixed L1 D cache: 32KB fixed L2 cache: mandatory, up to 2MB |
Software that is architecturally-compliant can run on either the Cortex-A53 or Cortex-A72 without modification, because they both implement the same architecture.