Question 3 More registers appears to be a good thing, in terms of reducing the t

Question

Question 3 More registers appears to be a good thing, in terms of reducing the total number of memory accesses a program might require. Using the arithmetic expression S A+B-(C+D support this statement. Hints: First, determine the number of memory accesses necessary using MARIE and the two registers for holding memory data values (AC and MBR). Then perform the same arithmetic computation for a processor that has more than three registers (for example, R1, R2, R3, R4) to hold memory data values.] [6 marks]

Explanation / Answer

Memory accessing in MARIE:

load a //loads a into AC

add b //adds b to a and stores in AC

store expr1 //stores sum in expression1

load c //loads c into AC

add d //adds c to d and stores in AC

store expr2 //stores sum in expression2

load expr1 //loads expr1

subt expr2 //subtract expr2 from expr1

store s //finally ,stores the result in s.

###Using registers R1,R2 and R3

add R1 a b //adds a and b then stores the result in R1

add R2 c d //adds c and d then stores the result in R2

sub R3 R1 R2 //subs R2 from R1 then stores in R3

store s R3 //Store final result in s

When using MARIE there are total of 9 memory accesses,whereas using more registers

decreases the memory accesses to 7.When we use more registers definitely the number

of instructions are reduced but the decrease in memory is marginal only.

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