Test: Instructions & Input Output Interface - Computer Science Engineering (CSE) MCQ

4 bits are for the opcode so number of 2 address instructions will be 2⁴ =16 ---so 14 double instructions are possible
But out of 16 only 14 are used so 2 are still left which can be used for 1 address instruction
For 1 address instruction we can use not only the 2 left over but also the 6 bits of operand1(to make it one address)--- so
6 bits that is 64 so they are laready 2 which each contains 64 so total 128 single address instructions -----so 127 single
instructions are possible
But out of 128 ,127 are used so 1 left which can be used for zero address instruction to make number of zero address we
can use the operand2 address 6 bits so total possible are 64 so total 1*64 = 64 zero address instructions are possible
So all encoding are possible

It is C.
Only the top of the stack can be accessed at any time. You can imagine a stack to be opened from only one side data
structure. So that if we put one thing over the other, we are able to access the last thing we inserted first. That is Last in

First Out (LIFO).
ROM is Read Only Memory.
PC points to the next instruction to be executed.
Not all instructions affect the flags.

The instruction opcode is a part of the instruction which tells the processor what operation is to be performed so it is not a form of memory while the others are

A 

We want to check for a particular bit position say 2 (third from right). Let the number be 0xA2A7 (last 4 bits being 0111).
Here, the bit at position 2 from right is 1. So, we have to AND this with 0x0004 as any other flag would give wrong value
(may count other bits or discard the bit at position "pos"). And 0x0004 is obtained by 0x1 << 2 (by shifting 1 "pos" times
to the left we get a flag with 1 being set only for the "pos" bit position).

Ans:(-16)
assume addresses start with 2000 for first instruction.
2000---add R2,R3,R4
2004--sub r5,r6,r7
2008---r1,r9,r10
2012--beq r1,offset //pc after instruction fetch of this instruction will be 2016,and branch target is 2000 ,offset will be (2016-16) = 2000
2016------next instruction

Answer => 500 bytes
Number of register = 64
Number of bits to address register = [log₂64] = 6 bits
Number of Instruction = 12
Opcode size = [log₂12] = 4
Opcode(4) reg1(6) reg2(6) reg2(6) Immediate(12)
Total bits per instruction = 34
Total bytes per instruction= 4.25
Due to byte alignment we cannot store 4.25 bytes, without wasting 0.75 bytes ,
So Total bytes per instruction = 5
Total instruction = 100
Total size = Number of instruction x Size of instruction 100 x 5= 500 Byes

No. of possible instruction encoding = 2¹¹ = 2048
No. of encoding taken by two-address instructions = 5 × 2⁴ × 2⁴ = 1280
No. of encoding taken by one-address instructions = 32 × 2⁴ = 512
So, no. of possible zero-address instructions = 2048 − (1280 + 512) = 256

The answer is TRUE.
RISC systems use fixed length instruction to simplify pipeline.
eg: MIPS, PowerPC: Instructions are 4 bytes long.
CISC systems use Variable-length instructions.
eg: Intel 80x86: Instructions vary from 1 to 17 bytes long.
Now the challenge is: How to fit multiple sets of instruction types into same (limited) number of bits (Fixed size instruction)?
Here comes Expanding opcode into the picture.
RISC systems commonly uses Expanding opcode technique to have fixed size instructions.

Answer should be D i.e branches off to ISR after completing current instruction.
CPU checks the status bit of interrupt at the completion of each current instruction running when there is a interrupt it service the interrupt using ISR.

Answer: B
A vectored interrupt is a processing technique in which the interrupting device directs the processor to the appropriate interrupt service routine. This is in contrast to a polled interrupt system, in which a single interrupt service routine must determine the source of the interrupt by checking all potential interrupt sources, a slow and relatively laborious process.

Ans is A.
Options B and D is obviously false.
A processor checks for the interrupt before FETCHING an instruction, So Option C is also false.

INTR is a signal which if enabled then microprocessor has interrupt enabled it receives high INR signal & activates INTA signal, so another request can’t be accepted till CPU is busy in servicing interrupt. Hence (A) is correct option.

In Programmed I/O, the CPU issues a command and waits for I/O operations to complete.
So here, CPU will wait for 1sec to transfer 10KB of data.
overhead in programmed I/O = 1 sec
In Interrupt mode , data is transferred word by word (here word size is 1 byte as mentioned in question "Data is transferred byte-wise").
So to transfer 1 byte of data overhead is 4 x 10^-6sec
Thus to transfer 10 KB of data overhead is = 4 x 10^-6 x 10⁴ sec
Performance gain
Thus, (b) is correct answer.