The Cortex family of ARM processors provides a range of solutions optimized around specific market applications across the full performance spectrum.
Cortex underlines ARM's strategy of aligning techna-ology around specific market applications and performance requirements.
The ARM Cortex family is comprised of three series, which all implement the Thumb-2 instruction set to address the increasing performance and cost demands of various markets
ARM Cortex-A Series, Aplication的意思
Applications processors for complex OS and user applications. 有MMU，这里就暗示只有A系列支持像linux这样的系统？
Supports the ARM, Thumb and Thumb-2 instruction sets.
ARM Cortex-R Series runtime的意思，要求实时性
Embedded processors for real-time systems.
Supports the ARM, Thumb, and Thumb-2 instruction sets
ARM Cortex-M Series MCU的意思，用在汽车上，无MMU，因为MMU会带来运行时间预测的不确定性
Deeply embedded processors
optimized for cost sensitive applications.
Supports the Thumb-2 instruction set only
它们都是Cortex的内核，是ARMv7的版本(不同于ARM7，ARM7的内核版本是ARMv4)。
Cortex-M系列的是MCU的意思
Cortex-R系列的是RunTime的意思
Cortex-A系列的是Application的意思
组合起来正好是ARM
架构一样，根据应用在某个地方加强了一下，比如A8为了应用，流水线增为8
M系列则是用在通用的且低成本的嵌入式处理器。