L-1.4:Types of Buses (Address, Data and Control) in Computer Organization and Architecture

Summary

In this educational video, the presenter delves into the intricacies of computer architecture, focusing on the types of buses and their functions. The address bus, carrying memory addresses, is explained with examples like the 8085 microprocessor, which has a 16-bit address bus allowing access to 65536 memory slots. The data bus, bidirectional and responsible for transferring data between components, is also discussed, with its size depending on the word size of the system. Lastly, the control bus, crucial for sending control and timing signals, is highlighted as essential for coordinating the execution of instructions. The video emphasizes the importance of understanding these fundamental concepts for a solid grasp of computer architecture.

Takeaways

• 🚌 **Types of Buses**: The video discusses three main types of buses in computer architecture: address bus, data bus, and control bus, each with specific roles.
• 📍 **Address Bus Function**: The address bus carries memory addresses to specify the location from which data is to be fetched or to which data is to be sent.
• 🔢 **Address Bus Calculation**: The number of bits in the address bus determines the total memory slots available, calculated as 2 raised to the power of the number of bits.
• 💾 **Example of Address Bus**: In the case of an 8085 microprocessor, a 16-bit address bus allows for 65536 memory slots.
• 🛤️ **Unidirectional Address Bus**: The address bus is unidirectional, meaning it is used to send addresses from the processor to memory or input/output devices but not the other way around.
• 📊 **Data Bus Bidirectionality**: Unlike the address bus, the data bus is bidirectional, allowing data to be transferred to and from the processor.
• 🔄 **Data Bus and Registers**: The data bus is used to transfer data between the processor, memory, and input/output devices, as well as within the microprocessor's internal registers.
• 🗂️ **Data Bus Size**: The size of the data bus is determined by the size of the word, which is the amount of data that can be stored at a memory location.
• ⏲️ **Control Bus Role**: The control bus carries control and timing signals, which are managed by the control unit to ensure proper instruction execution timing.
• 👨‍🏫 **Importance of Understanding Buses**: A clear understanding of how buses function is fundamental to grasping larger concepts in computer architecture.

Q & A

What are the three main types of buses in computer architecture discussed in the video?

The three main types of buses discussed are the address bus, data bus, and control bus.

What does the address bus carry in a computer system?

The address bus carries the memory addresses to which the CPU or microprocessor needs to access data.

How is the number of slots in memory determined by the address bus length?

The number of slots in memory is determined by 2 raised to the power of the address bus length in bits.

What is the length of the address bus in an 8085 microprocessor?

The length of the address bus in an 8085 microprocessor is 16 bits.

What does a 16-bit address bus allow for in terms of memory slots?

A 16-bit address bus allows for 2^16, or 65,536 memory slots.

What is the function of the data bus in a computer system?

The data bus is responsible for carrying the actual data between the CPU, memory, and input/output devices.

Is the data bus unidirectional or bidirectional?

The data bus is bidirectional, allowing data to be transferred both to and from the CPU.

What is the relationship between the size of the data bus and the size of the data or word in memory?

The size of the data bus is determined by the size of the data or word being transferred, which can be up to the maximum size of data that can be stored in a memory location.

What does the control bus carry and what is its purpose?

The control bus carries control and timing signals, which are used to coordinate the execution of instructions and manage the flow of data within the computer system.

Why is the control unit important for the proper functioning of a computer system?

The control unit is important because it generates the necessary control signals and timing for the execution of instructions, ensuring that operations are performed correctly and in the right sequence.

What advice does the presenter give to students trying to understand computer architecture?

The presenter advises students not to cram and instead focus on understanding the small concepts, as this will help them grasp the bigger concepts more effectively.

Outlines

00:00

🚌 Introduction to Buses in Computer Architecture

This paragraph introduces the topic of different types of buses in computer architecture and the basis for their design. It explains the roles of the address bus, data bus, and control bus. The address bus carries memory addresses, allowing the CPU to access specific locations in memory or input/output devices. The data bus facilitates the transfer of data between components, and it is bidirectional, unlike the address bus, which is unidirectional. The control bus carries control and timing signals, which are managed by the control unit to ensure proper execution of instructions. The paragraph uses the 8085 microprocessor as an example to illustrate these concepts, discussing the significance of the bus lengths in relation to the memory capacity and data size.

05:01

🔢 Understanding Data and Control Buses in Detail

The second paragraph delves deeper into the functionality of the data and control buses. It emphasizes the importance of the data bus's size, which is determined by the word size of the system, and in the given example, it is 16 bits, allowing it to carry two bytes of data. The paragraph also clarifies how the control bus operates, discussing the necessity of control signals for various operations such as loading data into registers, incrementing values, and memory read/write operations. The control unit's role in generating these signals and managing the timing of instruction execution is highlighted. The paragraph concludes with advice for students to understand these fundamental concepts thoroughly, as they form the basis for grasping more complex aspects of computer architecture.

Keywords

💡Bus

A bus in computer architecture refers to a subsystem that transfers data between components. It is a shared communication path that allows data, address, and control signals to be transmitted between different parts of a computer system. In the video, the presenter discusses different types of buses, such as the address bus, data bus, and control bus, highlighting their roles in facilitating communication within a computer.

💡Address Bus

The address bus is a part of a computer's hardware architecture that carries address information from the CPU to memory or input/output devices. It determines the maximum amount of memory that can be accessed by the CPU. In the script, the presenter uses the 8085 microprocessor as an example, explaining that its 16-bit address bus allows access to 65536 memory locations.

💡Data Bus

The data bus is responsible for transferring actual data between different parts of a computer system, such as between the CPU and memory or peripherals. It is bidirectional, meaning data can flow in both directions. The script mentions that the size of the data bus determines the amount of data that can be transferred at once, with the example of a 16-bit data bus being able to carry 16 bits of data.

💡Control Bus

The control bus carries control signals that manage the operations of the computer, such as timing and synchronization of various components. It is used by the control unit to coordinate the execution of instructions. The script explains that control signals are crucial for ensuring that instructions are executed correctly and in the right sequence.

💡Microprocessor

A microprocessor is a compact integrated circuit that contains the central processing unit (CPU) of a computer. It is the brain of the computer that performs most of the processing inside the computer. The video script uses the 8085 microprocessor as an example to illustrate how address and data buses interact with it.

💡Control Unit

The control unit is a part of the CPU that fetches instructions from memory, decodes them, and coordinates the operation of other parts of the computer to execute those instructions. It uses control signals that travel through the control bus. The script emphasizes the importance of the control unit in managing the timing and execution of instructions.

💡Memory

Memory in a computer system refers to the storage components that hold data and instructions for the CPU. The script discusses how the address bus is used to specify the location in memory from which data is fetched or to which data is written.

💡Input/Output Devices

Input/output (I/O) devices are hardware components that allow a computer to interact with the outside world. Input devices provide data to the computer, while output devices display or process data from the computer. The script explains how the address bus is used to access data from I/O devices.

💡Slots

In the context of the script, slots refer to the individual memory locations that can be addressed by the CPU. The number of slots is determined by the length of the address bus. For example, a 16-bit address bus provides 65536 slots, each of which can be uniquely addressed.

💡Bits

Bits are the smallest units of data in computing and communication. A bit can represent a logical state with two possible values, often interpreted as a 0 or 1. The script uses the term to describe the length of the address and data buses, with implications for the capacity and data transfer capabilities of the system.

💡Registers

Registers are small, fast storage components within the CPU used for temporarily holding data or instructions. The script mentions that data fetched from the data bus is often stored in registers before being processed.

Highlights

Introduction to the types of buses in computer architecture and their purposes.

Explanation of the address bus and its role in carrying memory addresses.

Description of the data bus for transporting data between components.

Role of the control bus in carrying control and timing signals.

Diagrammatic representation of the 8085 microprocessor and its associated control unit.

How the address bus facilitates data fetching from specific memory locations.

Calculation of memory slots based on the address bus length in bits.

Example of a 3-bit address bus and its corresponding memory slots.

Detailing the 8085 microprocessor's 16-bit address bus and its memory capacity.

The significance of the most significant bits (MSB) in addressing.

Functionality of the data bus as a bidirectional pathway for data.

Process of data transfer from input devices to the processor via the data bus.

The importance of the data bus in moving data between registers within the microprocessor.

Influence of the word size on the length of the data bus.

Handling of data size discrepancies through padding with zeros.

The control bus's function in sending control and timing signals for instruction execution.

The necessity of proper timing for instruction execution as managed by the control unit.

Use of control bus for operations like loading, incrementing, and clearing in registers.

Advice for students on understanding computer architecture by focusing on small concepts.

Transcripts

Hello friends, welcome to Gate Smashers

In today's video, we are going to discuss

Types of Buses in Computer Architecture

And generally, on what basis do we

make these busses?

That what is that bus carrying?

As you can see in the diagram, address bus, what is it carrying? address!

data bus for carrying the data

And control bus for carrying the control and timing signals

So here according to the diagram, you have.

8085 microprocessor And here we have control unit

And if we talk about address bus

So what is address bus carrying

The Address.

Like if we talk here in memory In memory or input and output devices

If I want to fetch anything

To reach any particular location

Then what does the CPU or microprocessor do for it?

Generates an address And that address will be generated from the address bus

And from any particular location we have to fetch the data

That location will be in the address bus

Like if we talk about 8085 microprocessor

So here the address bus length is 16 bits

16 bits means

Total number of slots in memory is 2 raised to power 16

Which is 65536

But if I talk about Let's take a simple example

The memory we have.

In that we have, this address bus The address bus length is let's say 3 bits

So what does it mean that in memory we have

8 slots 0, 1, 2, 3, 4, 5, 6 and 7

So total number of slots will be here? 7!

And it has 3 bits What does 3 bits mean?

That to represent it we have 00001001001110010110111

Means if we say that address bus its length is 3 bits

So what is it showing?

It is showing that 2 raised to power 3

Means 8 slots 8 locations in memory Which we can also call block

Means 8 places where the data can be read So generally if we talk about 8085

As I said 16 bits So total number of slots in memory is 2 raised to power 16

Which is 65536

So from these many slots

From where do I have to take data?

Let's say my slot number is this So I have to take x and its location is 101

So what will come in address bus?

101

And let's say if we have a value of 16 bits And if we have only address 101

So what will be the MSB bits?

Will be 0000

It's simple Address bit shows us

How many number of slots are there in memory?

And this is unidirectional

Means. processor generally generates address

And that address from where we have to take it?

Let's suppose from memory

we have to take some value from input device

Or we have to send any value to any output

So for that we use address bus here

Then if we talk about data bus First of all what is data bus?

Unidirectional means let's suppose if we talk here

Input device.

If we fetch anything from input device

Let's say we typed something from keyboard

So how will it go from there?

It will go first in data bus Let's say it goes in data bus

And from data bus it will go to processor

We have different types of registers near processor

Which we discussed in the previous video Data gets stored in those registers

So this is it basically

How we have to travel data And if we talk like this from microprocessor

Let's say I converted some input to output

And I have to show that data on printer

Or I have to show that data on monitor

which is an output device So how will we show?

From here that data will go And it will show in output device So to travel data

To send data we use data bus So it can go this way and the other way

So it is bidirectional And between the registers also

Where all registers are stored? In microprocessor So like we have data registers

Temporary registers In these registers also if we have to shift data

Then for that we use data bus only And how much this journey will be?

It depends on the size of your word Means like we talked about address

What address bit shows?

That how many locations we have in memory And the length of data bus depends on

The size of the data you are taking from this location

Let's say, that in any particular location I can store

2 bytes, Means the size of word we have

We discussed word in last video too

we use word basically to represent memory

And the size of word we have in this example That is 2 bytes

Means I can store 2 bytes in this location

2 bytes here, 2 bytes here, 2 bytes there

So what does it mean?

2 bytes means 16 bits So how many bits can data bus carry?

It can carry 16 bits This is how we represent with the data bus

So the length of data bus depends on The data you are storing in memory

Or the data you are taking from memory How much is that length?

And maximum length let's say If we talk

about memory Then we have 2 bytes in memory

And let's say the data coming from input is 1 byte

So there is no problem Now what will happen in 1 byte?

That the last 8 bits You give them value

And before that the MSB That will be 8 bits

0 0 0 0

It's simple

If the size of data or address is less

Then you give the LSB values the same And the MSB bits will be simply 0 0 0

Then we have control bus Control bus is basically used

To send control signals or timing signals

And for this we have dedicated hardware

Which is a control unit Because for which instruction to execute

There should be complete timing

It should not be that if I am executing the instruction later

Then it may be that there is a problem in my

output So generally we have control signals

Let's say if we talk about the register

Then we have to load the data in the register

So load is a signal Load means in that particular register

To load the data I have to activate the load If I want to increment any value

Then I can increment Let's say if I want to clear something

To clear we generate the control signals

If we talk about memory

Then if I want to perform read in memory

I want to read something from memory

Or write something in memory For this we have control signals

Which generates control unit And timing means

At what time clock pulse should be activated

That is what is done by the control unit

And all these signals travel through control bus If we talk about input

Then if I want to read something from input device

And write something from data So for all these values

We use control bus for all these purposes So this is simple

Although it is a very simple point

But if you want to understand computer architecture well

Then you have to keep these small points in mind

Only then you can do big concepts well

Students try to cram directly

Don't cram at all We will bring these small topics

And as soon as we relate all these topics And make a whole series

You will get much more benefit from it

So thank you, all the very best.