Microprocessors - Architectures and performances

The aim of this article is to summarize the most important aspects of microprocessor architecture. The concept of a microprocessor, which corresponds to an implementation of the processing unit function on a single circuit, is not far removed, in architectural terms, from processors in the general sense. That's why this introduction to microprocessor architecture not only refers to microprocessors alone, but places them in the more general context of the evolution of processor architecture.

Microprocessors are at the heart of the digital revolution. Thanks to their universality and performance, they enable the development of applications and solutions accessible to the greatest number of people. Their widespread use in digital systems makes them an essential component. Architectural characteristics and their links with software are fundamental elements in estimating the performance of a complete microprocessor-based solution, both for the development of a new system and for its use. The variety of application areas has led to a proliferation of microprocessor models, particularly in mobile systems. On the other hand, they are all based on identical architectural concepts. The aim of this article is to review these different concepts and show how they can be applied through examples of implementation. The main focus here is on personal computer and server microprocessors, while embedded systems use the same concepts in a more or less simplified way.

The main aspects developed in the article concern the internal architecture of instruction processing pipelines, which extract from the program to be executed the maximum number of instructions to be executed in parallel, the memory hierarchy, which limits the impact of main memory access times, and system support, which in particular enables the limited size of main memory to be virtualized and several applications to be managed at the same time, instruction sets, which are the link between software and hardware, interfaces to peripherals, which contribute to overall system performance, parallelism, which is a delicate source of performance to optimize, and finally, a few elements for assessing the performance of high-end microprocessors.