Pre-study- Instruction sets, Addressing Modes

Question 1

An ISA is defined as the design of a computer from the ___________ Perspective.

Answer 1

Programmer’s

Question 2

ISA include 3 types of MIPS instructions

Answer 2

Arithmetic/ Logic Instructions

Data Transfer Instructions

Branch and Jump Instructions

Question 3

ISA instruction - Arithmetic/ Logic Instructions

Answer 3

These Instructions perform various Arithmetic & Logical operations on one or more operands.

Question 4

ISA instruction - Data Transfer Instructions

Answer 4

These instructions are responsible for the transfer of instructions from memory to the processor registers and vice versa.

Question 5

ISA instruction - Branch and Jump Instructions

Answer 5

These instructions are responsible for breaking the sequential flow of instructions and jumping to instructions at various other locations, this is necessary for the implementation of functions and conditional statements.

Question 6

The ISA defines the maximum length of each type of ________.
Since the MIPS is a 32 bit ISA, each instruction must be accommodated within 32 bits.

Answer 6

instruction

Question 7

The ISA defines the Instruction Format of each type of instruction.
The Instruction Format determines how the entire instruction is encoded within 32 bits
There are 3 types of Instruction Formats in the MIPS ISA:

Answer 7

R-Instruction Format
I-Instruction Format
J-Instruction Format

Question 8

Binary _____ is false / OFF

Answer 8

Zero ( 0 )

Question 9

Binary ____ is true / ON

Answer 9

One ( 1 )

Question 10

8 bits equals _____ byte

Answer 10

One

Question 11

Binary is a _____ number system: counting done by a computer.

Answer 11

mathematics

Question 12

Addressing modes in computer architecture techniques are used to accommodate the following provisions:

Answer 12

It provides programming versatility to the user by including pointers to the memory, indexing of data, counters for loop control, and program relocation.

It reduces the number of bits in the addressing field of the instruction.

It also provides flexibility to the assembly language programmer in writing more efficient programs concerning the number of instructions and execution time.

Question 13

The _______ _______ refers to how the operand of an instruction is specified. It specifies a rule for interpreting/modifying the address field of the instruction before referencing the operand.

Answer 13

Addressing mode

Question 14

The control unit is designed to go through an instruction cycle divided into three major phases:

______ the instruction from memory:
Program Counter (PC) is one of the registers present in the system that keeps track of the program’s instructions stored in the memory. It holds the address of the next instruction to be executed and is incremented every time an instruction is fetched from memory.

_______ the instruction:
It determines the operation to be performed: the operands’ location and the instruction’s addressing mode. Further, the computer executes the instruction and returns to step 1 (fetching the instruction from memory) to fetch the next instruction in the sequence.

______ the instruction:
The addressing mode of the instruction is specified with a unique binary code that designates both the operation and the mode of the instruction. Instructions can be defined with a variety of addressing modes. Combining two or more addressing modes in one instruction is also possible.

Answer 14

Fetch
Decode
Execute

Question 15

type of addressing mode:

_______ / ______ _____ _____

The operands are implicitly specified in the instruction’s definition.
Consider the example, the instruction “complement accumulator” is an implied-mode instruction as the operand in the accumulator register is implied in the instruction definition. All register reference the instructions that use an accumulator are implied-mode instructions. Zero-address instructions in a stack-organized computer are also implied-mode instructions because the operands are implied to be on top of the stack.

Answer 15

Implied/ Implicit Addressing Mode

Question 16

type of addressing mode:

_________ ____________ _______

The operand is defined in the instruction itself. This mode instruction has an operand field instead of an address field. The operand field contains the actual operand used with the specified operation in the instruction. The immediate-mode instructions help initialize registers to a constant value.

            Instruction
   Opcode   |    Operand

ADD 8 will increment the value stored in the accumulator by 8.

Answer 16

Immediate Addressing Mode

Question 17

type of addressing mode:

_______ ________ ____________ _______

The operands that reside within the CPU are stored in the registers. The specific register is selected from a register field in the instruction. No reference to the memory is required to fetch the operand. The only difference between the Direct addressing mode and the register direct addressing mode is that the instruction address field refers to a CPU register instead of the main memory.

  Instruction                             Register:
Opcode  |  R        -------->   |   Operand

Advantage: This mode provides faster memory access to the operands.
Disadvantage: It has limited address space, and using multiple registers can help boost the performance, but it complicates the instructions.

Answer 17

Register Direct Addressing Mode

Question 18

type of addressing mode:

________ _________ ________ ______

The instruction defines a register in the CPU that stores the effective address of the operand in memory. Only one reference to the memory is required to fetch the operand. The specified register contains the address of the operand instead of the operand. The only difference between the Indirect addressing mode and the register indirect addressing mode is that the instruction address field refers to a CPU register.

                               [    ]                  [  ] [ Opcode | R ]  --->  [ EA  ] ----        [   ]
                              [     ]       |->     [ Operand]
                               [    ]                 [    ]
                          Reg Set              Memory

For example: ADD R1, R2: Here, the content of R2 is added to R1. R1 R2 represents registers.
Advantage: The instruction address field uses fewer bits to select a register than required to specify a memory address directly.

Answer 18

Register Indirect Addressing Mode

Question 19

type of addressing mode:

_____-_____ ________ ______

This mode is a special Register Indirect Addressing Mode case. The register is incremented/decremented after or before its value is utilized.
EA = content of the register.

The content of the register is increment automatically by step size ‘d’ after accessing the operand, where the step size ‘d’ depends on the size of the accessed operand. Only one reference memory is required to fetch the operand.

Answer 19

Auto-Increment Addressing Mode

Question 20

type of addressing mode:

_____-______ _________ ______

This mode is also a special Register Indirect Addressing Mode case.
EA = content of the register - step size.

The content of the register is decremented by step size ‘d’ after accessing the operand, where the step size ‘d’ depends on the size of the accessed operand. Only one reference memory is required to fetch the operand.

Answer 20

Auto-Decrement Addressing Mode

Question 21

type of addressing mode:

______ ______ _______

The effective address of the operand resides in the address field of the instruction.
The operand resides in the memory, and the address field of the instruction gives its address. Only one reference to the memory is required to fetch the operand, and no additional calculations need to be done to find the effective address of the operand. It is also known as absolute addressing mode.

For example, ADD X will increment the value stored in the accumulator by the value stored at X’s memory.

Answer 21

Direct Addressing Mode

Question 22

type of addressing mode:

______ _______ _______

The address field of the instruction gives the address of the memory location that contains the effective address of the operand. Two references to the memory are required to fetch the operand: The control fetches the instruction from memory and uses its address part to reaccess the memory that stores the effective address. This addressing mode slows down the execution as it requires multiple memory lookups to find the operand.

  instruction   [   I   ][  Opcode  ][ Operand ]

[ I ] is the mode bit

Answer 22

Indirect Addressing Mode

Question 23

type of addressing mode:

______ _____ ______

The indexed register content is added to the instruction’s address part to obtain the effective address of the operand.

EA = A + (R)
Here, the address field holds two values, A: Base value R: displacement value.

Answer 23

Displacement Addressing Mode

Question 24

type of addressing mode:

______ ______ ______

This mode is another version of the displacement address mode. The program counter’s content is added to the instruction’s address part to obtain the effective address.

EA = A + (PC)
Here, EA: Effective address, PC: program counter.

The instruction’s address part is usually a signed number that can be positive or negative. After the instruction’s address is fetched, the value of the program counter increases immediately, irrespective of whether the fetched instruction has been executed or not. PC: It contains the address of the next instruction to be executed.

Answer 24

Relative Addressing Mode

Question 25

type of addressing mode:

_____ ______ ______

The index register’s content is added to the instruction’s address to obtain the effective address.
EA = content of index register + Instruction address part

Answer 25

Indexed Addressing Mode

Question 26

type of addressing mode:

_____ _____ _____ ______

This mode is another version of the displacement address mode. To obtain the effective address, the base register’s content is added to the instruction’s address.
EA = A + (R)
A: Displacement, R: Pointer to the base address.

Answer 26

Base Register Addressing Mode

Question 27

type of addressing mode:

______ ______ ______

The operand resides at the top of the stack. Consider an example, ADD: This instruction will POP two items from the stack, add them, and at last, will PUSH the result to memory references of Addressing Modes.
It helps in reducing the number of bits in the instruction’s addressing field.
It facilitates pointers, indexing of data, and counters for loop controls.

Answer 27

Stack Addressing Mode

Question 28

_______ Addressing Mode: It initialize the register to a constant value.

Answer 28

Immediate

Question 29

______ Addressing Modes and _____ ______ Addressing Mode: It helps access static data and implement variables.

Answer 29

Direct
Register Direct

Question 30

______ Addressing Modes and ______ ______ Addressing Mode: It helps implement pointers and pass arrays as parameters.

Answer 30

Indirect
Register Indirect

Question 31

_______ Addressing Mode: It helps in program relocation at runtime. And in changing the sequence of instructions during execution.

Answer 31

Relative

Question 32

______ Register Addressing Mode: It helps in writing relocatable code and handling recursive procedures.

Answer 32

Base

Question 33

_____ Addressing Mode: It helps in the array and record implementation.

Answer 33

Index

Question 34

_____-______ Addressing Mode and Auto-Decrement Addressing Mode: It helps implements loops and stacks.

Answer 34

Auto-Increment

Question 35

Advantages of addressing modes

Answer 35

They improve performance by efficiently utilizing the CPU cache and reducing the memory read latency

Addressing Modes are used for implementing complex data structures in memory as they provide mechanisms such as indexing

Program sizes can be reduced drastically as the code can be compacted which allows faster execution of instructions

Addressing modes give you the flexibility to use different ways of specifying the address of operands in your instructions

Question 36

Disadvantages of Addressing Modes

Answer 36

Complexity: Particularly for inexperienced programmers, some addressing modes might be challenging to comprehend and use. Due to its intricacy, code may include errors or be inefficient

Limited Flexibility: Some addressing modes may limit the kind of operand operations that can be carried out. For instance, Immediate Mode restricts dynamic calculations to preset values only

Increased Memory Access: Because Direct and Indirect modes need more memory accesses to retrieve operands, program performance may be slowed down

Register Dependency: The availability of registers is very important for register modes. This can cause conflicts and inefficient resource utilization in systems with a finite number of registers

Code Size: Certain addressing modes could provide longer and more complicated instructions, increasing the code size

Question 37

What are addressing modes in computer architecture?

The operation field of instruction in a computer specifies the operation to be performed. The Addressing mode refers to how the operand of an instruction is specified.

Answer 37

It specifies a rule for interpreting/modifying the address field of the instruction before referencing the operand.

Question 38

Why addressing mode is used?

The Addressing mode refers to how the operand of an instruction is specified. We can specify how an operand’s effective address is represented in any particular instruction by using the addressing modes.

Answer 38

There is only one memory reference needed and no additional computation.

Question 39

What are the 5 addressing modes?

Answer 39

The addressing mode include Register Mode, which places the operand in a register, Immediate Mode, which places a constant value in the instruction, Direct Mode, which places the operand address in the instruction, Indirect Mode, which places the address in a register, and Indexed Mode, which determines the address using the base register and offset.

Question 40

What are addressing modes and its types?

Answer 40

Computer architecture’s addressing modes control how a processor accesses information in memory while carrying out an instruction. The five main types are Indexed Mode, Register Mode, Immediate Mode, Direct Mode, and Indirect Mode.