When the Poky source code is downloaded, what is actually copied is the metadata and the BitBake tool. Additional source code is fetched on demand. One of the main features supported by BitBake is source code fetching.

This support has been designed to be as modular and as flexible as possible. Every Linux-based system includes the Linux kernel and several other utilities that form the root filesystem, such as OpenSSH or a Linux kernel.

The OpenSSH source code is available from its upstream website as a tar.gz file hosted on an HTTP server, while the Linux kernel release is usually hosted on a Git repository, and those two different source codes can easily be fetched by BitBake.

BitBake offers support for many different fetcher modules that allow the retrieval of tarball files and a number of other protocols, such as Git, Subversion, Bazaar, OSC, HTTP, HTTPS, FTP, CVS, Mercurial, Perforce, and SSH.

The mechanism used by BitBake to fetch the source code is internally called as fetcher backends that are configurable to align the user's requirements and optimize fetching the source code .