L-2.3: Immediate Addressing Mode | Computer Organisation and Architecture

Summary

In this educational video, the concept of immediate addressing mode is explored, which is crucial for understanding computer memory and instruction execution. Immediate addressing mode allows direct use of constant values within instructions, eliminating the need for computation or memory access. This mode is beneficial for competitive exams and academic assessments, offering a straightforward approach to handling constants like pi or e. The video highlights the advantages of this mode, such as simplicity and directness, and discusses its limitation regarding the size of the constant, which must fit within the address field of the instruction. The summary concludes with a note of thanks, emphasizing the importance of this addressing mode in computer science.

Takeaways

• 📚 Immediate addressing mode is a method where the operand is directly provided as a constant within the instruction.
• 🔑 In this mode, there's no need for computation to determine the operand's value because it's directly given in the instruction.
• 💡 The immediate addressing mode is denoted with hashtags (#), indicating that the operand is a constant value.
• 🔄 Constants used in programs, like mathematical constants π and e, are ideal for immediate addressing mode as their values remain unchanged.
• ❌ Variables, which can change during program execution, are not suitable for immediate addressing mode due to the potential for value alteration.
• 🚀 This addressing mode is beneficial for competitive exams and academic assessments, providing a clear understanding of how constants are handled in assembly language.
• 💼 The main advantage of immediate addressing mode is the simplicity and speed it offers by dealing directly with constants without additional memory or computation.
• 📉 A limitation of immediate addressing mode is that the size of the constant must fit within the address field of the instruction, which is typically limited by the architecture.
• 🧩 The range of the operand in immediate mode is constrained by the length of the address field, which can restrict the size of the constants that can be used.
• 🔍 Understanding immediate addressing mode helps in grasping fundamental computer architecture concepts and how instructions are executed in lower-level programming.

Q & A

What is immediate addressing mode?

Immediate addressing mode is a method where the operand is directly provided as a constant within the instruction itself, meaning the data is given directly without the need for computation or memory access.

How does immediate addressing mode differ from other addressing modes?

In immediate addressing mode, the operand is a constant and is directly embedded in the instruction, whereas in other modes, the operand might be a variable stored in memory or a register, requiring computation to determine its value.

Why is immediate addressing mode beneficial for competitive exams and academic assessments?

Immediate addressing mode is beneficial because it simplifies understanding of instruction sets and memory management, which are key concepts in computer architecture and often tested in exams.

What is the significance of the hashtag symbol in immediate addressing mode?

The hashtag symbol (#) is used to denote that the following value is an immediate operand, indicating that the value is a constant and not an address or a register.

Can you provide an example of an instruction using immediate addressing mode?

An example of an instruction using immediate addressing mode could be 'add r1, #3', which means add the constant value 3 to the contents of register r1.

Why is immediate addressing mode particularly useful for constants?

Immediate addressing mode is useful for constants because their values do not change during program execution, so providing the value directly in the instruction avoids the need for memory or register allocation.

What is the limitation of immediate addressing mode regarding the size of the operand?

The limitation of immediate addressing mode is that the size of the operand must fit within the address field of the instruction, which is typically limited by the architecture of the processor.

How does the length of the address field affect immediate addressing mode?

The length of the address field determines the range of constants that can be used in immediate addressing mode. If the constant is too large, it may not fit within the address field, requiring a larger instruction size or a different addressing mode.

What is the advantage of immediate addressing mode in terms of computation?

The advantage of immediate addressing mode is that it eliminates the need for computation to determine the operand's value, as the constant is directly provided in the instruction, thus speeding up the execution process.

How does immediate addressing mode compare to using variables in a program?

In contrast to using variables, which may require memory or register allocation and potential computation to determine their values, immediate addressing mode provides the constant value directly, simplifying the instruction and reducing the need for additional memory or computation.

Outlines

00:00

💡 Understanding Immediate Addressing Mode

The paragraph introduces the concept of immediate addressing mode in computer programming, where the operand is directly provided as a constant within the instruction itself. This method simplifies the process as it eliminates the need for computation to determine the operand's value. The speaker explains that in immediate addressing, constants such as the value of pi or e are directly used in the instruction, which is beneficial for competitive exams and educational assessments. The example 'add r1,3' is used to illustrate how a constant value (3) is added to the content of a register (r1). The use of hashtags is mentioned as a way to denote immediate addressing mode, emphasizing the direct and computation-free nature of this addressing mode.

05:01

🚧 Limitations of Immediate Addressing Mode

This paragraph discusses the limitations of immediate addressing mode, primarily the constraint on the size of the constant that can be used. The operand's range is dependent on the length of the address field within the instruction, which must be large enough to accommodate the constant's size. The speaker uses a hypothetical 16-bit instruction size to explain how the address field's length dictates the maximum value of the constant that can be used. If a constant exceeds this limit, the instruction size must be increased. The paragraph concludes by summarizing the key points about immediate addressing mode, including its advantages of direct constant usage and computation avoidance, as well as its disadvantage of a limited constant range.

Keywords

💡Immediate Addressing Mode

Immediate addressing mode is a method used in computer programming where the operand is directly provided as a constant within the instruction itself. This mode is particularly useful for executing operations with constants that do not change throughout the program. In the video, the speaker uses the example 'add r1, 3' to illustrate how the immediate value '3' is directly added to the value in register 'r1' without the need for any computation or memory access.

💡Operand

An operand is a piece of data that is operated on by the instruction in a computer program. It can be a constant, a variable, or a memory address. In the context of immediate addressing mode, the operand is a constant value that is directly included in the instruction, as opposed to being stored in a memory location or register.

💡Opcode

Opcode stands for operation code and refers to the part of an instruction that specifies the operation to be performed. It is a fundamental concept in computer architecture, as each instruction in a program contains an opcode that tells the processor what action to take. In immediate addressing mode, the opcode is accompanied by the immediate operand, as seen in the script where the opcode 'add' is used with the immediate operand '3'.

💡Constants

Constants are fixed values that do not change during the execution of a program. They are used in immediate addressing mode to provide direct values within the instruction. The video explains that constants like the value of pi (3.14) or e (2.7) can be used as immediate operands because their values remain constant throughout the program's execution.

💡Effective Address

The effective address is the memory location where the actual data is stored. In immediate addressing mode, the concept of effective address is simplified because the operand is a constant and does not require computation to determine its memory location. The video emphasizes that no computation is needed to calculate the effective address when using immediate addressing mode.

💡Instruction

An instruction is a command given to a computer's processor that specifies an operation to be performed. It typically consists of an opcode and one or more operands. In the video, the immediate addressing mode is discussed in the context of how instructions are structured and how they use immediate operands to perform operations.

💡Memory Location

A memory location refers to a specific address in a computer's memory where data or instructions are stored. In the context of immediate addressing mode, the video explains that there is no need to access a memory location to retrieve the operand since it is provided directly within the instruction.

💡Register

A register is a small, fast storage location built into the processor of a computer. Registers are used to store temporary data during program execution. The video mentions registers when discussing how immediate values are added directly to the values stored in registers, such as in the example 'add r1, 3'.

💡Variables

Variables are used to store data that can change during the execution of a program. The video contrasts variables with constants, explaining that variables cannot be used as immediate operands because their values may change, unlike constants. Variables require storage in memory or registers and cannot be directly embedded in the instruction like constants.

💡Address Field

The address field in an instruction is the portion of the instruction that specifies where the operand or data is located. In immediate addressing mode, the address field is not used to point to a memory location but instead holds the constant value directly. The video discusses how the size of the address field can limit the range of constants that can be used as immediate operands.

Highlights

Immediate addressing mode is discussed in detail, beneficial for competitive exams and academic assessments.

Immediate addressing mode is where the operand is directly provided as a constant.

In immediate mode, the value of the operand is directly given in the instruction without computation.

Immediate addressing mode is denoted with hashtags, indicating direct data.

Constants like the value of pi or e are used in immediate addressing mode as they remain unchanged throughout the program.

Immediate addressing mode allows direct use of constants without the need for memory or register storage.

Variables cannot be used directly in immediate addressing mode due to the possibility of their values changing.

The instruction execution process is explained, emphasizing the immediate availability of constant values.

Immediate addressing mode is contrasted with variable usage, which requires memory or register storage.

The benefits of immediate addressing mode include dealing with direct constants and no computation required.

A limitation of immediate addressing mode is the range of the operand, which depends on the length of the address field.

The address field's length determines the range of constants that can be used in immediate addressing mode.

If the constant value exceeds the address field's limit, the instruction size must be increased.

An example of a 16-bit instruction size is provided to illustrate the limitations of immediate addressing mode.

The video concludes with a summary of the key points about immediate addressing mode.

Thank you note to the viewers for watching the video on immediate addressing mode.

Transcripts

Hello friends, welcome to Gate Smashers

In today's video, we are going to discuss immediate addressing mode

And in this video,

we are going to discuss all the important points about immediate addressing mode

Which will be very beneficial for your competitive exams or college or university level exams

So first of all, what is immediate addressing mode?

Where operand is directly provided as constant

What does it mean?

That we have instruction

In instruction, we have opcode and with opcode, we have operand

Means what is given here?

Address is given

Now in immediate mode, what is the value of this address?

Means we have directly data given in this

Means we don't have to do any computation

Direct data is given in place of this operand

And what is that data actually?

That data is constant

So generally we use constants in immediate address mode

In immediate addressing mode

For example, if I write let's say add r1,3

So what does it mean?

In r1 register, we have to add 3 in r1 value

So we generally denote immediate addressing mode with hashtags

And what is this 3 value?

This 3 value is direct data

Means you have to calculate it directly as data and operand

You don't have to do any computation as memory or register

So that's why no computation required to calculate the effective address

To calculate effective address, you don't need any computation

Why?

Because we have direct data given in instruction

So whenever we use constants in programs

What does it mean?

Immediate addressing mode helps there

What is the reason for this?

Because the value of constant will remain same in the whole program

Means if I write a program of C

And in the program of C, if I take constant anywhere

Constant means like value of pi, value of e

All these are the values of pi and e, what is this?

It is constant

So if you take only one value of pi and e in the whole program

Then it will be constant

So for this you don't need to store value in memory or register

You give direct value at this place

Means the value of e is 2.7 or pi is 3.14

You give that value directly in the instruction

So instruction directly contains that data

So that you don't have to do any computation

You don't have to go to any memory location

You don't have to go to any register

That you will go there and pick up the data

Why?

Because we are using only constants here

So the addressing mode that helps us to use constants

That is called immediate addressing mode

And opposite of this if we talk about variables

So we use constants very quickly

Like constant int a is equal to 10

Means the value of a will remain same in the whole program

We don't have to do any other changes to a

So we gave it directly at this operand place

10

But if we take normal variable

Let's say int a is equal to 10

Now we can't give the value of normal variable

At the place of direct operand

The reason for that is

That it can be possible in the program

I have to do some changes to its value in the future

Because it is variable

So the data in variable can be changed

So if we put the data in place of direct operand

Then later during the time of computation

Because when the instruction is executed

First we fetch the instruction

Decode the instruction

After decoding it is executed

So when this instruction is executed

Then only we will know what is the actual value of a

So we have to execute at that time

At that time we will know what is the value of a

So whenever we use variables

Then we have to store them in memory

Or in registers

But if we talk about here in immediate mode

So directly you are dealing with constants

So give the value of constant directly in the instruction

So you need no extra memory location

No register

And you will not have to do any computation

That you go to that place and pick up that data

Because as soon as you fetch the instruction

And decode the instruction

What did you get by decoding

You got the opcode and the operand

So you don't need to execute it

Before that you have the data in your hand

But the other addressing modes

Like where we discuss with variables

And deal with variables

There we have to do computation

So if we talk about the addressing mode

What is the benefit?

The first benefit is that we are dealing with direct constants

And the second thing is that no computation is required here

We will get the value of operand without computation

But a small limitation here is that

The range of operand

Depends on the length of your address field

Means the length of the address field

Should be the size of the constant

If the value of the constant is greater than this

Then you will have to increase the value of the instruction

Let's say that we have the size of the instruction

16 bit

So what happens in 16 bit

We use 1 bit to represent the mode

Direct mode, indirect mode

We use 3 bit for opcode

And let's say we are using 12 bit for address field

For operand

So if we talk about the immediate mode

The value of the constant in the immediate mode

Means it is fixed

It should be within 2 raised to power 12

Means it should be between 0 to 2 raised to power 12 minus 1

If the number is greater than this

Then how will you denote it here

For that you have to increase the memory or the address field of the instruction

So here on the address field

The length of the address field depends on that

That how much will be the range of the constant

This is a small limitation in the immediate addressing mode

So in this video we discussed the main thing

What is the immediate addressing mode

And what are its advantages and disadvantages

And this is all about the immediate addressing mode

Thank you