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:
“Casting an eye on the education of children, from whence I can make a judgment of my own, I observe they are instructed in religious matters before they can reason about them, and consequently that all such instruction is nothing else but filling the tender mind of a child with prejudices.”
—George Berkeley (1685–1753)
“Stories of law violations are weighed on a different set of scales in the Black mind than in the white. Petty crimes embarrass the community and many people wistfully wonder why Negroes don’t rob more banks, embezzle more funds and employ graft in the unions.... This ... appeals particularly to one who is unable to compete legally with his fellow citizens.”
—Maya Angelou (b. 1928)