L-2.1: What is Addressing Mode | Various Types of Addressing Modes | COA

Summary

In this educational video, the concept of addressing modes in computer architecture is explored, emphasizing its significance in programming and exams. Addressing modes dictate how operand bits in instructions are interpreted, whether as direct data, memory addresses, or register numbers. The video outlines the benefits of addressing modes, such as reducing instruction size by using registers instead of memory addresses, and facilitating features like pointers, looping, and indexing. It introduces various addressing modes including immediate, direct, and indirect, and sets the stage for a detailed discussion in the next video.

Takeaways

• 💡 Addressing mode is a crucial concept in computer organization and architecture, frequently appearing in competitive exams and academic curricula.
• 📝 The script explains that an instruction typically contains an opcode and an operand, where the operand refers to the data on which operations are performed.
• 🔍 Addressing mode clarifies how operand bits in an instruction should be interpreted, whether as direct data, memory addresses, or register numbers.
• 👨‍💻 The video highlights the practical application of addressing modes in programming, especially when dealing with variables and constants.
• 📉 Addressing modes can reduce the number of bits required in an instruction by utilizing registers instead of direct memory addresses, thus compacting instruction size.
• 🔄 The script introduces various types of addressing modes including implied, immediate, register, indirect, direct, auto-increment, decrement, and others, which are essential for different programming scenarios.
• 🏢 RISC systems typically have 4 to 6 addressing modes, while CISC systems may have more, reflecting the complexity and flexibility in handling data.
• 🔑 Addressing modes facilitate advanced programming concepts like pointers, where the address of a variable is used in place of the data itself.
• ➕ They also support looping constructs and counters through auto-increment and decrement modes, streamlining repetitive operations.
• 🔄 The concept of relocation is discussed, explaining how addressing modes help in adjusting memory addresses when a program is moved to a different location in memory.

Q & A

What is an addressing mode in computer architecture?

An addressing mode is a way to determine how the operand of an instruction is used. It tells the CPU how to interpret the bits in the operand to access the data it needs to perform an operation.

Why are addressing modes important in computer organization?

Addressing modes are important because they allow for efficient use of memory and registers, reduce the size of instructions, and provide flexibility in how data is accessed and manipulated during program execution.

What are the benefits of using addressing modes?

Using addressing modes can reduce the number of bits required in an instruction, facilitate the use of pointers and looping constructs, and support features like indexed addressing and relocation.

What is the difference between an operand and an opcode in an instruction?

An operand is the data or address that an instruction operates on, while an opcode is the part of the instruction that specifies the operation to be performed, such as addition or subtraction.

How does an addressing mode help in the case of variables in programming?

Addressing modes help with variables by allowing the instruction to refer to the data indirectly through a register or memory address, rather than embedding the actual data value directly in the instruction.

Can you give an example of how addressing modes are used with constants in programming?

When a constant value like Pi is used in a program, the addressing mode might allow the instruction to directly embed the constant value in the operand, simplifying the instruction and potentially reducing its size.

What is the purpose of the indirect addressing mode?

The indirect addressing mode is used when the operand contains an address that points to the actual data location. This allows for multi-level indirection where the address in the operand leads to another address that contains the data.

How do auto-increment and auto-decrement addressing modes work?

Auto-increment and auto-decrement addressing modes automatically adjust the address in the operand by a specified amount after each access. This is useful for iterating through data structures like arrays or for implementing loops.

What is the role of addressing modes in supporting indexed data access?

Indexed addressing modes allow the CPU to access data based on a base address and an offset. This is useful for accessing elements in arrays or for implementing algorithms that require data access based on a variable index.

Why is addressing mode crucial for relocation in computer systems?

Addressing modes are crucial for relocation because they help in adjusting the addresses of instructions and data when a program is moved from one memory location to another, ensuring that the program can execute correctly regardless of its location in memory.

Outlines

00:00

💡 Introduction to Addressing Modes

The speaker introduces the concept of addressing modes in computer architecture, emphasizing its importance in competitive exams and academic studies. Addressing modes are crucial for understanding how instructions in a computer program interact with data. The speaker explains that instructions typically consist of an opcode (operation code) and an operand (data). The operand can be data itself, or it can be an address where the data is stored, such as in memory or registers. Addressing modes dictate how these operands are treated within an instruction, whether as direct data, memory addresses, or register numbers. The paragraph sets the stage for a deeper exploration of addressing modes and their significance in various programming scenarios.

05:00

🔑 Benefits and Types of Addressing Modes

This paragraph delves into the benefits of addressing modes, such as reducing the number of bits required in an instruction by using register numbers instead of memory addresses. The speaker illustrates this with an example of a 1M memory size requiring 20 bits for addressing, but only 4 bits if using register numbers. Addressing modes also facilitate the use of pointers, looping with automatic increment and decrement, and indexing. The paragraph lists various types of addressing modes, including implied, immediate, register, indirect, direct, auto-increment, decrement, relative address mode, indexed addressing mode, and base register. The speaker notes that RISC systems typically have fewer addressing modes compared to CISC systems, which can have more complex and varied addressing modes.

10:01

🔄 Addressing Modes in Practical Computing

The final paragraph discusses the practical applications of addressing modes in computing. It explains how addressing modes help in executing instructions that involve variables, pointers, and looping. The speaker mentions that the value of variables is determined at runtime, and addressing modes are essential for accessing this data during instruction execution. The paragraph also touches on the concept of relocation, where the execution of a process may occur at different memory locations over time, and addressing modes help in adjusting the memory addresses accordingly. The speaker concludes by stating that the next video will explore each addressing mode in detail, promising a deeper understanding of how these modes facilitate various programming tasks.

Keywords

💡Addressing Mode

Addressing mode refers to the way in which a processor specifies the location of an operand, which is the data it operates on. In the context of the video, addressing modes are crucial for understanding how instructions interact with data in computer architecture. The video explains that addressing modes determine whether an operand represents direct data, a memory address, or a register number. This concept is foundational to the video's theme, as it sets the stage for discussing various types of addressing modes and their applications in programming and computer operations.

💡Operand

An operand is the data that an instruction operates on. In the video, the term is used to explain that in programming, operations such as addition or subtraction are performed on data, which can be constants or variables. Operands are integral to the video's discussion of addressing modes because they are the elements whose addresses or values are manipulated by these modes. The video clarifies that operands can be stored in memory or registers, and addressing modes dictate how these operands are accessed during instruction execution.

💡Opcode

Opcode stands for operation code and represents the part of an instruction that specifies the operation to be performed, such as addition, subtraction, or multiplication. The video uses opcode in the context of explaining the structure of an instruction, which typically includes both an opcode and an operand. Understanding opcodes is essential for grasping how addressing modes fit into the larger picture of instruction execution, as opcodes define the actions to be taken on the data pointed to by operands.

💡Memory

Memory refers to the computer's storage where data and instructions are held. In the video, memory is discussed in relation to where operands can be stored. Addressing modes are important because they determine how the processor retrieves data from memory. The video explains that operands can be direct data or the address of data stored in memory, highlighting the significance of memory in the context of addressing modes and instruction execution.

💡Registers

Registers are small, fast storage locations within the CPU used to hold temporary data. The video mentions registers as an alternative to memory for storing operands, which can help reduce the size of instructions. By using registers, the video suggests that addressing modes can facilitate more efficient data access and manipulation, as register numbers can be represented with fewer bits than memory addresses, thus saving space in the instruction set.

💡Direct Addressing Mode

Direct addressing mode is one of the types of addressing modes discussed in the video, where the operand directly contains the memory address of the data. This mode is straightforward and efficient for accessing data because the address is explicitly provided in the instruction. The video implies that direct addressing is a fundamental mode that allows for quick data retrieval, which is essential for performance in computer systems.

💡Indirect Addressing Mode

Indirect addressing mode is another addressing mode mentioned in the video, where the operand contains the address of another location that holds the actual data. This mode is useful for implementing pointers and accessing data through intermediate addresses. The video explains that indirect addressing allows for more complex data access patterns, such as those used in linked data structures or when working with pointers in programming.

💡Indexed Addressing Mode

Indexed addressing mode is used when data is accessed through a base address plus an offset. The video suggests that this mode is beneficial for accessing elements in arrays or performing operations on blocks of data with a common base address. Indexed addressing is a powerful concept in the video's discussion of addressing modes, as it enables efficient access to sequential data structures, which are common in programming.

💡Relocation

Relocation in the context of the video refers to the process of adjusting memory addresses in code or data when a program is moved to a different memory location. This concept is important for understanding how programs can be executed in different environments or memory spaces without hardcoding specific addresses. The video implies that addressing modes play a role in relocation by allowing for flexible address interpretation that can be adjusted as needed.

💡Instruction Size

Instruction size refers to the number of bits or bytes required to represent an instruction in a computer's architecture. The video discusses how addressing modes can influence instruction size, particularly in terms of reducing the number of bits needed to specify operands. By using registers or other compact addressing modes, the video suggests that the size of instructions can be minimized, which can lead to more efficient use of memory and potentially faster execution.

Highlights

Addressing mode is a crucial topic in computer organization and architecture.

Addressing modes are important for competitive exams and college/university level exams.

An instruction typically contains an opcode and an operand, where the operand refers to data.

Opcode represents the operation such as addition, subtraction, or multiplication.

In micro-instructions, data is not directly included but rather the address of the data.

Addressing mode determines how to treat operand bits in an instruction.

There are various types of addressing modes, including implied, immediate, register, indirect, direct, and more.

Addressing modes can reduce the number of bits needed in an instruction by using registers instead of direct memory addresses.

Addressing modes facilitate the use of pointers in programming by interpreting operand bits as memory addresses.

Auto-increment and auto-decrement addressing modes are used for looping and counters in programs.

Indexed addressing mode allows for data indexing, which is useful in arrays and similar data structures.

Relocation is made possible by addressing modes, which is essential when a program's memory location changes.

Addressing modes help in executing instructions that involve variables, whose values are determined at runtime.

Immediate mode allows for passing direct values in instructions, which is different from using variable values.

The video will cover each addressing mode in detail in the next part.

Transcripts

Hello friends, welcome to Gate Smashers

In today's video, we are going to discuss what is an addressing mode

and what are the types of addressing mode

If we talk about computer organization and architecture

then addressing mode is one of the most important topic

because if you talk about any competitive exam

or if you talk about college or university level exam

then there also you will definitely get the question of addressing mode

and it is a very simple topic

First in this video I am going to tell you what is addressing mode

What are the benefits of addressing mode and what it is providing us

and then what are the types of addressing mode

which we will explain one by one

So here if we talk about what is an addressing mode

So if we talk about instruction

which we are discussing about in the previous videos

So generally in instruction what we have in instruction

Opcode and operand

What is operand generally?

Operand means data

Means which data you have to work on

and what is opcode? Operation

Means plus, minus, multiplication

Now on what you will do plus minus multiplication?

Will do on data only

Like we write programs in simple C

A is equal to 10, int B is equal to 20

C is equal to A plus B

Means we are doing addition or subtraction

So the data which we pass

This data

What we are saying about operand is actually

We are talking about data

But if we talk about an instruction

If we talk about any micro-instruction

Then in instruction we don't have data directly

What can we have?

The address of that data can be

Means the data which we are bringing in the computer

Whatever data is coming, which we are passing in the programs

That data is either saved in our memory

Or that data is saved in our registers

So what we are writing operand here

Whatever data we are writing here

Whatever bits we are writing here

What are those bits actually representing?

Are they directly representing data?

Or are they representing some address of memory?

Or are they representing some number of register?

What is that actually?

We get to know from addressing mode

So addressing mode basically tells us

That how to treat these operand bits

Means how to consider them

This actually tells us addressing mode

So here if we talk

We can give direct data here

Or we give the address that we generally give here

Why? Because if we talk about programming

Then in programming we work on variables

We work on constant

If we are giving directly constant

In any C program we are giving direct constant value

Let's say we are giving the value of constant Pi

Now what is the value of Pi? It is constant

Now if you are giving this constant value

Then you can give that data directly in the instruction

But generally we work on variables

We can also work like this in variables

Like if I have data

A is equal to B * C

Now here when will A come

A value will come when we execute B * C

Means when this instruction will be executed

After that I will get to know the A value

Now this A value

How can I give it in the instruction?

When I will get to know after the execution of the instruction

That what is the value of A

Then we can never give the value of data

Directly in the instruction

Means you can't write directly

Subtraction 2

Or subtraction 3

Or multiplication 4

What do we actually give?

We work on variables

So whenever we talk about variables in programs

Or we ask the user for data many times

We write scanf

So scanf is when we ask the user for data

At run time

When the program runs and is executed

At that time we take data from the user

So for these type of instructions

We can't give the data directly in the instruction

So here I have these bits

How we have to treat them

How to consider them

That actually tells us

Addressing mode

So generally the variables we have

They are generally saved in our memory

Whatever data they have

Or where they are saved

They are saved in the registers

So there we have the data given in operand

Is it address?

Is it the number of the register?

These bits how to consider

This tells us addressing modes

So addressing modes are different types of addressing modes

Which I have written here

Implied, immediate, register, indirect, direct

Auto increment, decrement, direct addressing mode

Relative address mode

Indexed addressing mode, base register

So if we talk about the risk environment

If we talk about the risk systems

Reduced instructions

So there we have

Near about 4 to 5 or 5 to 6 addressing modes

But the CISC computers

Means the complex instruction computers

There we have many times

Many addressing modes

It depends

In different computers

Different computer organizations

Different addressing modes can be

But generally

In the risk system

There are 5 to 6 addressing modes

Which tell us that these bits

Whatever value is written in operand

Whatever address is written

How to treat it

Now if we talk here

What is the benefit of addressing mode

The first benefit of addressing mode

That number of bits

We can reduce in the instruction

How?

Let's say

If we have a memory

And the size of the memory

Let's say 1M

Means 1 million words

There are 1M words in this whole memory

Now in these 1M words

Your instruction can be anywhere

Your data can be anywhere

Now if you give in the instruction

Address

Where is your data

So obviously the size of your address

Will be 20 bits

Because 1M is the location here

So to represent 1M locations

How many bits do we use?

20 bits

So the space of your address in the instruction

Which is the space of operand

How many bits will it be?

It will be 20 bits

And we also have opcode bits

So the size of your instruction

Will increase

So we can keep data in the register

If we talk

Let's say we have 16 registers

Number of registers is 16

So obviously in 16 registers

Where can the data be read

Any register can have data read

So if I want to represent 16 registers in bits

How many bits will I use?

4 bits

How?

From 0 to 15 number of registers

Total registers will be 16

And if we want to represent 16 from 0 to 15

How many bits do we use?

4 bits

So if we want to reduce the size of the instruction

Then we can keep the data in the register

And we can pass the register number in operand

So how many will be here?

How many bits will be here instead of 20 bits?

4 bits

So the size of this will be reduced

So this basically provides the facility to the programmer

That you can reduce the instruction size

You can reduce the bits

Apart from this

If we talk about

Let's say we use pointers in our program

What is a pointer?

Let's say if I say int a is equal to 10

Now what will happen?

A variable will be saved in memory

And the value in it will be 10

Now this location

Let's say the location is 100

Now if I pass the pointer

Let's say there is a pointer ptr

And what will we do in ptr?

We will pass address of a

So address of a is 100

So what value will come in ptr?

100

So here we are using the pointer

We will go to a location

Let's say this is my memory

We checked operand

The value in operand was 100

We went to 100 location

The data in 100 location

Is it our direct data?

Or is it also an address?

We also know this through

Addressing mode

It may be that the value is 200

Now what to consider 200?

Is it an address?

Or is it data?

If we talk about indirect mode

So what does indirect mode say?

That yes, this is also a location ahead

Means you will have to go to 200 location from here

Whatever data is there in 200 location

10, 20

Pick it up and use it

So if we want to facilitate pointers here

Then we can use the addressing mode here

Or if we talk about counters

Let's say if we talk about looping

There is a for loop, for i is equal to 1 to 10

Now here we want that if

For i is equal to 1 to 10 is written

And we printf it

So what does it mean?

Here 1 to 10 automatically increments

So automatically for increment and decrement

We have a facility in addressing mode

Apart from this, indexing

If we want to put indexing in the data

Then we also have the facility of indexing

Indexed addressing mode

And apart from this we have relocation

Relocation means

Let's say I have a data

Means the data is in the memory

The data is in 100 to 200

Any process is there in 100 to 200

Now in that process

Or in those instructions we have written

Whatever instruction is written on 100

Let's say go to

170 location

Means jump to 170

Now here you will go to 170

Whatever instruction is written

You will pick up that instruction

But what happens is

We use the funda of relocation

Means when this process is executed by CPU

Or will use it

In future if this process comes again

Then it is not necessary that it gets the same location

It may get a different location

Means now it may be between 500 to 600

This process is now fit between 500 and 600

Now here if I write go to 170

Then what will happen?

It will go to such an address

Which is actually invalid

Means go to 170 means

According to this question

It should have been go to 570

It should have been at 70

But who changes the addresses?

To relocate these addresses

We also use the concept of addressing mode

So addressing mode provides many facilities and benefits

That is what

Basically if we are using looping

Or if we are using pointers

Or if we are using variables here

All the variables we use

The value of the variables is calculated at run time

At execution time

So if we want to bring the data at that time

Then addressing mode only helps there

We do not pass data directly in the instruction

There are some modes

Like there is an immediate mode

I will bring them in detail one by one

But here I am giving a simple example

There are many instructions

In which we can also pass direct value

But what we write in most of the code

We use variables

So when the data of variables comes

When we run the instruction

When one instruction is run

After that we get to know the other data

So at that time we

Can't pass the data inside the instruction

So these are different benefits of addressing modes

Which help us to execute all these points

So now we will see all these modes in detail one by one in the next video

Thank you.