The machine instruction sets are (almost by definition) different on
each machine where as runs. Floating point representations
vary as well, and as often supports a few additional
directives or command-line options for compatibility with other
assemblers on a particular platform. Finally, some versions of
as support special pseudo-instructions for branch
optimization.
This chapter discusses most of these differences, though it does not include details on any machine's instruction set. For details on that subject, see the hardware manufacturer's manual.