Question

How many memory refernces are required for fetching and executing each of the following instructions?

(a)ADD 50(R­₁),R₂    b)SUB (R­₁)+R­_2­

Answer 1

1). 1 instruction fetch, 1 fetching from indexed location and 1 to store into indexed location

Total 3 memory references .

2 ).   1 instruction fetch, 1 fetching from indirect location and 1 to store into indirect location

Total 3 memory references .

Comments

Register access is a memory access? And what about instruction fetch - the question explicitly says this though it does not give instruction size.

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sir plz provide link about that topic .

Answer 2

(a)ADD 50(R­₁),R₂ 

one for accessing R2,

one for acessing R1 and then adding 50+(R1) ---1 for execution and then again accessing 50+(R1)...so total 3fetches + 1 execution

b)SUB (R­₁)+R­_2­

one for accessing R2,

one for acessing R1 and then again accessing (R1)...so total 3 fetches + 0 executes

considering (R­₁) as register indirect mode

Comments

aren't R1 and R2 registers? What about instruction fetch?

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Yes I am wrong . . .  I have considered number of references for calculation of addresses . . . I did not see the ques properly I thought just references