PlatformIO ecosystem has decentralized architecture. Build scripts, toolchains, the pre-built tools for the popular OS (Mac OS X, Linux (+ARM) and Windows) are organized into the multiple development platforms.
Each development platform contains:
PlatformIO Build System based build scripts for the supported frameworks and SDKs
Pre-configured presets for embedded boards
Pre-compiled toolchains and relative tools for multiple architectures.
A platform name or its specific version could could be specified using platform option in Project Configuration File platformio.ini.