Target hardware that can run RTEMS is often referred to simply as the target because RTEMS is specifically aimed at that target hardware. An RTEMS executable is statically linked and executes in a single address space on the target hardware. A statically linked executable means the RTEMS Kernel, drivers, third-party packages and application code is linked into a single executable image. A single address space means no virtual memory and no memory protected process address space is running within the RTEMS arena and the RTEMS executive, drivers and application have unprotected access to the whole address space and all hardware.
Target hardware supported by RTEMS has a Board Support Package or BSP. A BSP is a specific instance of an RTEMS architecture that allows the creation of an RTEMS executable. You can view the layering as:
RTEMS targets are grouped by architectures and within an architecture there are a number of Board Support Packages or BPSs. An architecture is a specific class or family of processors and can be large such as ARM or specific such as the NIOS-II or Microblaze.
RTEMS is designed to be ported to new target hardware easily and efficiently.