otprint and a simple boot process. Microcontroller software is easier to comprehend with a smaller team (single person) of engineers but proprietary in nature and more complicated to expand in features and to maintain long-term. The advantage of a microprocessor and a Linux based system is that the os is mature, long term maintainable and portable to future (roadmap) devices. This is a key reason to design on a microprocessor, and in fact one of the main justi- fications of moving to an O-RAN based system: making the 3GPP protocol stack into "just another application running on Linux" allows it to benefit from standard microprocessor roadmaps rather than custom chip designs from a few specialized (and expensive) vendors. Over the last few decades, Linux has been ported to a plethora of processor architectures, including Power Architecture, Microprocessor without Interlocked Pipelined Stages (MIPS), Arm, RISC-V and obviously x86. These days, most support is centered on the latter three: Arm, RISC-V and x86. Given that 3rd Generation Partnership Project (3GPP) stack application complexity and size are continuously grown (as we showed in the O-RAN overview chapter), only very few commercial base station implementations rely on a microcontroller/RTOS environment to run anything outside of the (low) Physical Layer (and even that is optional) stacks. The trend clearly is towards abstraction of software into portability, re-use and standardization, as sup- ported by Linux. Open Radio Access Network (O-RAN) Systems Architecture and Design. DOI: https://doi.org/10.1016/B978-0-323-91923-4.00010-0 © 2022 Elsevier Inc. All rights reserved. Open Radio Access Network (O-RAN) Systems Architecture and Design Table 5-1 Microcontroller and microprocessor characteristics. Microcontroller Microprocessor Operating system Bare metal or RTOS Higher order os such as Linux Storage for Operating System On-chip External (flash) memory and Application Complexity Simple Complex Application space Bounded Almost any Footprint Small, limited ex