When you choose a QNX partition, the secondary boot loader (sometimes called the OS loader) starts.
This loader is Neutrino-specific, resides on the QNX partition, and depends on the type of filesystem.
Power-Safe filesystem
For a Power-Safe (fs-qnx6.so) filesystem, the secondary boot loader validates the filesystem and locates the most recent stable snapshot. It then presents
all appropriate files from the .boot directory as a scrolling list, from which you can select the required boot image.
QNX 4 filesystem
For a QNX 4 filesystem, the secondary boot loader displays a message to start loading the operating system.