Static and Dynamic Relocation

Introduction

This shows the basic hardware instruction cycle for a machine that uses static relocation and for one that uses dynamic relocation.

Static Relocation

Static relocation refers to address transformations being done before execution of a program begins. A typical hardware instruction cycle looks like this:

loop
    w := M[instr_ctr];          (* fetch instruction *)
    oc := Opcode(w);
    adr := Address(w);
    instr_ctr := instr_ctr + 1;
    case oc of
    1:  reg := reg+M[adr];    (* add *)
    2:  M[adr] := reg;        (* store *)
    3:  instr_ctr := adr;     (* branch *)
    ...
    end
end (* loop *)

Dynamic Relocation

Dynamic relocation refers to address transformations being done during execution of a program. In what follows, the function NL_map (for Name Location map) maps the relocatable (virtual) address va given in the program into the real (physical) storage address pa:

pa := NL_map(va)

loop

    w := M[NL_map(instr_ctr)];      (* fetch instruction *)
    oc := Opcode(w);
    adr := Address(w);
    instr_ctr := instr_ctr + 1;
    case oc of
    1:  reg := reg+M[NL_map(adr)];  (* add *)
    2:  M[NL_map(adr)] := reg;      (* store *)
    3:  instr_ctr := NL_map(adr);   (* branch *)
    ...
    end
end (* loop *)