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Direct instruction (DI) is the explicit teaching of a skill set using lectures or demonstrations of the material to students. A particular subset, denoted by capitalization as Direct Instruction , refers to the approach developed by Siegfried Engelmann and Wesley C. Becker that was first implemented in the 1960s.
An indirect branch (also known as a computed jump, indirect jump and register-indirect jump) is a type of program control instruction present in some machine language instruction sets. Rather than specifying the address of the next instruction to execute , as in a direct branch , the argument specifies where the address is located.
Definition: A direct instruction is one that specifies in the instruction itself the address of the source or destination register whose contents will be the subject of the instruction. Definition: An indirect instruction is one that specifies a "pointer register", the contents of which is the address of a "target" register. The target register ...
Also, depending on how it specifies the address of the new instruction sequence (the "target" address), a branch instruction is generally classified as direct, indirect or relative, meaning that the instruction contains the target address, or it specifies where the target address is to be found (e.g., a register or memory location), or it ...
Indirect addressing does carry a performance penalty due to the extra memory access involved. Some early minicomputers (e.g. DEC PDP-8, Data General Nova) had only a few registers and only a limited direct addressing range (8 bits). Hence the use of memory indirect addressing was almost the only way of referring to any significant amount of memory.
This distinction is due to the fact that a direct perspective focuses only on immediate actions related to instruction, such as classroom observation and curriculum development, whereas an indirect perspective broadly focuses on indirect activities, such as creating the school climate, as well as direct activities.
In the IBM System/360, for example, the branch instructions BAL or BALR, designed for procedure calling, would save the return address in a processor register specified in the instruction, by convention register 14. To return, the subroutine had only to execute an indirect branch instruction (BR) through that register.
Indirect threading uses pointers to locations that in turn point to machine code. The indirect pointer may be followed by operands which are stored in the indirect "block" rather than storing them repeatedly in the thread. Thus, indirect code is often more compact than direct-threaded code.