IBM System/370 assembler concepts: Which statement best describes a key assembler function related to base registers on System/370?
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AAllows the programmer to write base registers and displacements explicitly in the source program.
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BKeeps track of which general-purpose registers are available as base registers and what base addresses they contain.
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CAllows multiple programs to reside in separate areas of core at the same time.
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DRefers to the control programs of an operating system.
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ENone of the above
Answer
Correct Answer: Keeps track of which general-purpose registers are available as base registers and what base addresses they contain.
Explanation
Introduction / Context:IBM System/360/370 assemblers use a base-displacement addressing model. Understanding how assemblers manage base registers is critical for writing and maintaining low-level code that addresses memory efficiently and relocatably.
Given Data / Assumptions:
- The assembler supports USING/DROP directives to assign base registers to address ranges.
- Programmers use base-displacement forms in instructions.
- The question asks about the assembler’s role in tracking base registers.
Concept / Approach:While programmers specify addressing forms, the assembler maintains a base register table derived from USING statements. This table records which general-purpose registers act as bases and the corresponding base addresses, enabling translation of symbolic references into correct displacements. Multitasking or multiple-program residence is an OS feature, not an assembler language property, and “control programs” refers to OS components, not the assembler itself.
Step-by-Step Solution:
Recognize that base register management is an assembler bookkeeping task.Associate USING directives with internal tables: register → base address.Identify the statement that describes this tracking responsibility.Exclude unrelated OS features (multiple programs in memory) and terminological confusion about control programs.Verification / Alternative check:Assembler manuals document the base register table and relocation assistance provided during assembly based on USING/DROP.
Why Other Options Are Wrong:Explicit syntax (option A) is true in practice, but the distinctive assembler function is the tracking of base registers (option B). Options C and D concern operating system behavior, not assembler responsibilities.
Common Pitfalls:Assuming the OS, not the assembler, resolves addressability issues; or conflating base management with runtime register contents.
Final Answer:Keeps track of which general-purpose registers are available as base registers and what base addresses they contain.