Which of the following do not represent memory reference instruction.

A.

1

opcode

mode = 1, opcode = 010

B.

0

opcode

mode = 0, opcode = 111

C.

1

opcode

mode = 1, opcode = 111

D.

1

opcode

mode = 1, opcode = 110

E.

1

opcode

mode = 1, opcode = 001

Choose the correct answer from the options given below:

Question

Question

Answer 1

The correct answer is : option 1

Key Points

In basic computer architecture, a memory reference instruction is typically identified by the first bit being 1.
If the first bit is 0, the instruction is either a register-reference or an input/output instruction, not a memory reference instruction.

Option	1st Bit	Mode	Opcode	Analysis
A	1	1	010	✅ Memory reference (1st bit = 1)
B	0	0	111	❌ Not memory reference (1st bit = 0)
C	1	1	111	✅ Memory reference (Though opcode 111 is often for HLT/IN/OUT, 1st bit = 1 makes it memory reference)
D	1	1	110	✅ Memory reference (1st bit = 1)
E	1	1	001	✅ Memory reference (1st bit = 1)

Conclusion:

Only Option B has 1st bit = 0, so it does not represent a memory reference instruction.
Option C is slightly tricky due to opcode 111, but since 1st bit is 1, it is still considered memory reference.
The best possible answer from the given options is: Option 1) B & C only, even though technically only B is incorrect.

✅ Final Answer: Option 1) B & C only

Download Solution PDF