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Consider an instruction of the type $\text{LW R1, 20(R2)}$ which during execution reads a $32$-$bit$ word from memory and stores it in a $32$-$bit$ register $R1.$ The effective address of the memory location is obtained by adding a constant $20$ and contents of $R2.$ Which one best reflects the source operand?

  1. Immediate addressing 
  2. Register addressing 
  3. Register Indirect addressing 
  4. Indexed addressing
in CO and Architecture by Boss (16.7k points)
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Why is (C) wrong?

2 Answers

+6 votes
Best answer

Answer must be D) Indexed addressing

  • Address field stores starting address and Index register stores a signed number (displacement )
  • Suitable for iterative operations, array implementation .
  • Register R2 acts as index register and 20 is  the Base address.

Edit: ISRO has corrected the answer in revised key :)

by Boss (32.4k points)
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+1 vote

The given answer key of this question is also wrong. It is given as C) Register Indirect addressing but answer should be D) Indexed addressing.

https://gateoverflow.in/2123/gate2011_21

by Loyal (9.6k points)

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