Simple embedded application does not need the support of embedded operating system such as single chip microcomputer, and can realize specific functions directly with assembler. There are many applications to run, so you need an operating system to manage them.
General mobile phone products, small medical equipment and military equipment all use the platform of arm+linux.
At present, the Arm processor (CPU) is widely used, and the embedded operating system can be varied, not just linux. Embedded linux system is relatively stable, with open source code, low cost and strong portability. It can flexibly cut unnecessary functions, reduce the size of embedded software and reduce system power consumption. So many embedded linux operating systems are used. But now many companies are using commercially customized embedded linux platforms to reduce the amount of development and speed up the development (for example, some are dedicated to communication equipment and some are dedicated to general consumer electronics), so it is necessary to buy them.