GATE CS 1994 Q1.21 — Memory Management and Virtual Memory

To find the correct statement, let us analyze each option:

• Option A: Macro definitions cannot appear within other macro definitions in assembly language programs
  In standard assembly language macro processors, while macro calls can be nested, nesting of macro definitions (defining a macro inside another macro definition) is generally not permitted. Thus, this statement is true.
• Option B: Overlaying is used to run a program which is longer than the address space of a computer
  Overlaying is a technique used to run programs that are larger than the available physical memory (RAM), not the logical address space. A program cannot exceed the maximum addressable space of the CPU. Thus, this statement is false.
• Option C: Virtual memory can be used to accommodate a program which is longer than the address space of a computer
  The size of virtual memory is strictly bounded by the logical address space of the computer (determined by the CPU's word size, e.g., $2^{32}$ bytes for a 32-bit architecture). A program cannot have an address space larger than what the processor can address. Thus, this statement is false.
• Option D: It is not possible to write interrupt service routines in a high-level language
  Interrupt Service Routines (ISRs) can indeed be written in high-level languages like C or C++ (often utilizing compiler-specific keywords like __interrupt or inline assembly). Thus, this statement is false.

Therefore, the only true statement is A.