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250 Part 2 ½ Regions7of Computer Space

Section 2 ½ Memory Hierarchies and Multiple Processes

usable only for addressing variables within the scope of the current addressing environment. Reference to variables beyond the scope of the current environment is accomplished by a stuffed IRWS. This causes the addressing to be accomplished by addressing relative to the base of the stack (BOS) in which the variable is located.

The IRWS contains information specifying the stack number (Stack No,), the location (DISF) of the related MSCW, and the displacement (5) of the parameter relative to the MSCW. The absolute memory location of the sought parameter is formed by adding the contents of DISP and 5 to the base address of the referenced stack. The base address of the stack is determined by accessing the stack descriptor as described previously. The information contents of the stuffed IRWS with the exception of d , is dynamic in nature and must therefore be accumulated as the program is executed. The contents of the stack number (Stack No.) and DISP fields are entered into the IRWS by a special hardware operator which is invoked by the software whenever the program attempts to pass a parameter by name.



Burroughs [1964]; Burroughs [1965]; Randall and Russell [1964].

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