Complex sentence: The ultimate extension of this are "Directly Executable High Level Language" designs, in which each statement of a high-level language such as PL/I is entirely and directly executed by microcode, without compilation.
Split into simpler sentences: The ultimate extension of this are "Directly Executable High Level Language" designs. In these, each statement of a high level language such as PL/I are entirely and directly executed by microcode, without compilation.