ARM products are becoming increasingly diverse, and their naming conventions are also expanding. Many people are asking: What do ARM core and architecture mean? What is the relationship between core and architecture? For example, what does the ARMv7 architecture refer to?
1. ARM Cores: From ARM7 and ARM9 to Cortex-A7, A8, A9, A12, A15, and then to Cortex-A53 and A57, different versions of ARM have different design philosophies. For example, the Cortex A8 and A9, designed for high speed, are based on the ARMv7a architecture; the Cortex M3 and M4 are based on the ARMv7m architecture; the former refers to the core, while the latter refers to the instruction set architecture.
2. ARM's architecture is based on the RISC instruction set, and its core is just the foundation of the hardware architecture that implements this instruction set. It is a subset of the Thumb-2 instruction set architecture (ISA), which includes all the basic 16-bit and 32-bit Thumb-2 instructions. The Harvard processor architecture can execute instruction fetching while loading/storing data, and has a three-stage pipeline with branch prediction, etc.
3. Imagine you're building a house. Initially, due to low skill levels, single-story houses were popular. This is one type of architecture (V5T). You can design a single-story house with a separate bathroom, which is called the ARM7 core. Then, other people (chip design companies) who want to build houses buy your blueprints and build them. After a while, some people feel that a separate bathroom isn't enough; they also want a small yard! Okay, then ARM will meet your requirements and release a model with a small yard (ARM9).
A long time passed, and this single-story building structure continued to be modified to meet everyone's needs. Later, ARM discovered that everyone's building capabilities had skyrocketed (including process technology, design capabilities, and clock speed), and building only single-story houses wasn't enough! Okay, to keep the designers busy, ARM introduced a two- or three-story building style. Since this was completely different from the single-story design, it was called a new architecture (ARMv6). Similarly, ARM also prepared models with swimming pools and garages for this building style (ARM11). Okay, they continued to modify and modify until everyone was able to build buildings with more than ten stories. ARM, as always, released a new model (ARMv7 architecture). At this point, ARM felt that the previous names were too old-fashioned, such as ARM5, ARM6, and ARM7—both unpleasant to hear and hard to remember. "I want to give it a name that sounds impressive, so that we can at least be considered designers of skyscrapers," they said. So, the subsequent cores were all called Cortex.
The name change was only part of the story. With the development of this architecture, ARM realized that previously, the buildings constructed using their blueprints were only suitable for residential use. And what's the point of residential buildings? Low power consumption, of course. Now things are different. Buildings constructed using their blueprints can now be used not only for residential purposes, but also for military bases and high-end office buildings. Previously, only Intel could design such advanced buildings! To meet these diverse needs, ARM divided the architecture into three series (M series, R series, and A series).
The M series is designed for residential buildings, because ordinary people value affordability, and these buildings are typically around ten stories high (low power consumption). The R series is designed for military bases, and these buildings are also not very tall—around ten stories high—but the key is to have the ability to respond quickly to special situations (fast interruption). Finally, the A series is for business tycoons, so of course it needs to be high-end, classy, and high-performance, with all sorts of LED lights and light shows.
