Instruction Set
The VAX instruction set was designed to be powerful and orthogonal. When it was introduced, many programs were written in assembly language, so having a "programmer-friendly" instruction set was important. In time, as more programs were written in higher-level language, the instruction set became less visible, and the only ones much concerned about it were compiler writers.
One unusual aspect of the VAX instruction set is the presence of register masks at the start of each subprogram. These are arbitrary bit patterns that specify, when control is passed to the subprogram, which registers are to be preserved. Since register masks are a form of data embedded within the executable code, they can make linear parsing of the machine code difficult. This can complicate optimization techniques that are applied on machine code.
Read more about this topic: VAX
Famous quotes containing the words instruction and/or set:
“Everything from airplanes to kitchen blenders—and even chopsticks—comes with an instruction manual. Children, despite all their complexity, do not.”
—Lawrence Kutner (20th century)
“I move my thin legs into your office
and we work over the cadaver of my soul.
We make a stage set out of my past
and stuff painted puppets into it.”
—Anne Sexton (1928–1974)