L-1.3:Various General Purpose Registers in Computer Organization and Architecture

Summary

This video from the Gate Smashers series delves into the intricacies of computer organization, focusing on various types of registers. It explains the purpose and size of registers like the address, data, accumulator, program counter, instruction, temporary, input, and output registers, typically 16 bits in size. The video aims to clarify how these registers interact within a computer system, using examples to illustrate their roles in data storage, instruction execution, and memory addressing. It also touches on concepts like direct and indirect addressing, promising a deeper exploration in upcoming videos.

Takeaways

• 💡 Computer organization is a complex subject that intertwines both hardware and software, often leading to confusion among students.
• 📚 The presenter aims to clarify concepts sequentially to help students understand the interaction between hardware and software.
• 🔗 The previous video discussed the connection of registers with the common bus and the use of multiplexers, which is foundational for understanding registers.
• 📏 Different types of registers include the address register, data register, accumulator, program counter, instruction register, temporary register, and input/output registers, each serving a specific function within the computer system.
• 📉 Registers are typically 16-bit, but can also be 8-bit or 32-bit, and their size is measured in bits, which corresponds to their capacity to store information.
• 🔢 The size of a register is crucial as it determines the amount of data it can hold, with the example given using a 16-bit system where a 'word' is equivalent to 2 bytes.
• 🏷 The address register is used to access specific memory locations by storing the address of the data or instruction to be fetched.
• 📊 The accumulator serves as a temporary storage for intermediate data, such as the result from an ALU operation before it is further processed or stored.
• 🔄 The program counter holds the address of the next instruction to be executed, ensuring the sequence of operations is maintained.
• 📝 The instruction register stores the complete instruction, including the opcode and operand, which dictates the operation to be performed and the data location.
• 🔄 Temporary registers are used to hold data temporarily during processing, typically 16 bits in size, similar to other main registers.
• 🖥️ Input and output registers facilitate the transfer of data between input/output devices and the computer's processing units, with the input register being simplified to 8 bits in the example.

Q & A

What is the main challenge students face when studying computer organization?

The main challenge students face when studying computer organization is that it involves both hardware and software concepts, which they often try to cram, leading to a lack of understanding of how the hardware and software actually work together.

Why is it important to watch the previous video on connecting registers with the common bus?

It is important to watch the previous video on connecting registers with the common bus to understand how registers are interconnected and how the circuitry is implemented with the help of multiplexers, which provides a foundation for discussing different types of registers.

What is the general size of registers used in computer systems?

The general size of registers used in computer systems is 16 bits, although they can also be 8 bits or 32 bits depending on the system's architecture.

What does the size of a register determine?

The size of a register determines the amount of data it can hold, typically measured in bits. For example, a 16-bit register can hold 16 bits of data.

What is a 'word' in the context of computer organization?

In computer organization, a 'word' is a memory representational unit used to represent memory. It is not limited to 1 byte and can be multiple bytes, depending on the system architecture, such as 32 bits or 64 bits.

How is the size of the memory in the example script calculated?

In the example script, the size of the memory is calculated as 4096 words, with each word being 16 bits, making it a total of 4096 * 16 bits of memory.

What is the purpose of an address register?

The purpose of an address register is to hold the address of the word in memory from which data needs to be fetched. It provides the memory with the location to access and retrieve the data.

What is the size of the address register in the given example?

In the given example, the size of the address register is 12 bits, which corresponds to the number of words in memory (4096), represented as 2^12.

What is the role of the accumulator in a computer system?

The accumulator is used to store intermediate data. It holds data temporarily, such as when converting input to output or before giving it to the ALU for processing.

What is the size of the accumulator in the example provided?

In the example provided, the size of the accumulator is 16 bits, which is the same as the size of a word in the system.

What does the program counter register store?

The program counter register stores the address of the next instruction to be executed. It always points to the location of the upcoming instruction in the memory.

What addressing mode is represented by a 0 in the most significant bit of the instruction?

A 0 in the most significant bit of the instruction represents direct addressing, where the address specified in the operand is the exact location of the data.

What is the size of the instruction register in the example?

In the example, the size of the instruction register is 16 bits, which includes the opcode and the operand address.

What is the purpose of a temporary register?

A temporary register is used to store temporary data during processing. It holds data that is needed for short-term use in calculations or operations.

What is the size of the temporary register in the script's example?

In the script's example, the size of the temporary register is 16 bits, allowing it to store data equivalent to the system's word size.

What is the function of an input register?

An input register is used to collect data from input devices, such as a keyboard, and then pass that data to the ALU or accumulator for further processing.

What is the size of the input register in the given example?

In the given example, for simplicity, the input register is 8 bits, although this size can be increased based on the system's requirements.

What is the role of an output register?

An output register is responsible for receiving data from the ALU and then sending it to output devices, such as a printer, scanner, or monitor.

Outlines

00:00

💡 Introduction to Computer Organization and Registers

This paragraph introduces the topic of the video, which is different types of registers in computer organization. The speaker emphasizes the complexity of the subject for students, who often struggle with understanding both hardware and software aspects. The video promises to clarify these concepts sequentially. It also references a previous video on connecting registers with a common bus using multiplexers, suggesting that viewers should watch it for better understanding. The paragraph concludes by listing various types of registers such as address, data, accumulator, program counter, instruction, temporary, input, and output registers, and mentions that the size of these registers is generally 16 bits, although they can vary.

05:03

🔢 Understanding Register Size and Memory Representation

The speaker explains the concept of register size and memory representation, using a 16-bit system as an example. They discuss how memory is organized into words, which can be multiple bytes depending on the system architecture. The paragraph delves into the size of the address register, which is determined by the number of words in memory, and in this case, is 12 bits due to a 4096-word memory size. The data register size is explained to be equivalent to the word size, which is 16 bits. The accumulator's role as a storage for intermediate data is also highlighted, along with its size being 16 bits. The program counter's function of holding the address of the next instruction is detailed, and its size is also identified as 12 bits.

10:08

📚 The Role of Instruction Register and Addressing Modes

This paragraph focuses on the instruction register and the concept of opcodes and operands within instructions. The format of an instruction is explained, with the opcode indicating the operation to be performed and the operand specifying the data location. The most significant bit (MSB) is introduced to differentiate between direct and indirect addressing modes. The paragraph also discusses the size of the instruction register, which is 16 bits, accommodating both the opcode and the operand address. The temporary register's purpose for storing temporary data and the input and output registers' roles in handling data from and to devices are briefly mentioned, setting up the stage for further discussion in the next video.

Keywords

💡Registers

Registers are high-speed storage locations within a computer's central processing unit (CPU) used to hold data or instructions temporarily during processing. In the video, various types of registers are discussed, such as address, data, and program counter registers, which are integral to the functioning of computer hardware and software. The script mentions that registers can be 8-bit, 16-bit, or 32-bit, with 16-bit being the common size, highlighting their importance in computer organization.

💡Address Register

An address register is a type of register used to store memory addresses. It is essential for accessing data in memory, as it holds the address of the data to be fetched. In the script, the address register is described as picking up data from memory by holding the address, which the memory then decodes to retrieve the correct data. The size of an address register is determined by the memory size, such as 12 bits for a 4096-word memory.

💡Data Register

A data register is used to store the actual data being processed. It can hold the data temporarily before it is sent to other parts of the CPU or memory. The script explains that the size of a data register is typically the size of a word, which in the example given is 16 bits, corresponding to the size of the data that can be stored or retrieved at one time.

💡Accumulator

An accumulator is a register that holds intermediate results during arithmetic or logical operations. It is used to store data temporarily before it is sent to memory or used in further operations. The video script uses the accumulator as an example of a register that would store data coming from the ALU (Arithmetic Logic Unit), emphasizing its role in data processing.

💡Program Counter

The program counter is a register that keeps track of the address of the next instruction to be executed. It is fundamental to the instruction execution flow in a computer. The script illustrates that after an instruction is fetched, the program counter updates to point to the next instruction's address, showing its role in sequence control.

💡Instruction Register

An instruction register is used to hold the instruction currently being executed. It is crucial for the CPU to understand what operation to perform. The video script details that the instruction register contains both the opcode, which defines the operation, and the operand, which provides the data location or value for the operation, making it a key component in instruction execution.

💡Temporary Register

A temporary register is used to store data temporarily during various operations. It can hold intermediate results or data that needs to be accessed quickly. The script mentions the temporary register as a place to store data, highlighting its utility in quick data retrieval and manipulation within the CPU.

💡Input Register

An input register is used to store data coming from input devices, such as a keyboard. It serves as an intermediary between the input device and the CPU, allowing the data to be processed. The script simplifies this concept by stating that the input register can be 8 bits for simplicity, showing its role in handling user input.

💡Output Register

An output register is used to store data that is to be sent to output devices, such as a printer or monitor. It holds the data until it is ready to be output. The script explains the output register's function in taking data from the ALU and sending it to output devices, emphasizing its role in the final stage of data processing.

💡Word

In the context of computer organization, a 'word' is a fixed-size piece of data that a computer can process at one time. The script uses the term 'word' to describe the size of data that can be stored in memory and registers, such as a 16-bit word, which is equivalent to two bytes. This concept is central to understanding data size and memory addressing.

💡Opcode

An opcode is a part of an instruction that specifies the operation to be performed. It is crucial for the CPU to know what action to take, such as addition, subtraction, or other operations. The script explains that the opcode, along with the operand, is stored in the instruction register, indicating its importance in defining the nature of the instruction.

Highlights

Introduction to the concept of registers in computer organization, emphasizing the complexity due to the intersection of hardware and software.

Sequential explanation of computer organization concepts to provide clarity on how hardware and software interact.

Explanation of how registers are connected to the common bus using multiplexers, with a reference to a previous video for more details.

Discussion on different types of registers, including address, data, accumulator, program counter, instruction, temporary, input, and output registers.

Clarification on the general size of registers, typically 16-bit, but also mentioning 8-bit and 32-bit options.

Description of the memory size as 4096*16, providing a context for understanding the size of registers in terms of memory architecture.

Explanation of the term 'word' in computer organization, its relation to memory representation, and its variability in size.

The role of the address register in fetching data from memory by providing the memory with the address of the required word.

The size of the address register, determined by the number of words in memory, which in this example is 12 bits.

The function of the data register as a storage location for data, with a size corresponding to the word size of 16 bits.

The purpose of the accumulator to store intermediate data before it is processed by the ALU.

The program counter's role in storing the address of the next instruction, highlighting its importance in instruction sequencing.

The size of the program counter, which is determined by the memory's addressable size, in this case, 12 bits.

The instruction register's function to store the entire instruction, including opcode and operand, for execution by the ALU.

The size of the instruction register, which accommodates the 16-bit instruction format.

The role of the temporary register in storing temporary data during computation processes.

The input register's function to receive data from input devices and prepare it for processing by the ALU or accumulator.

The output register's role in handling data from the ALU to be sent to output devices, such as printers or monitors.

A teaser for the next video, which will delve into the connectivity of registers, instruction fetching, decoding, and output conversion processes.

Transcripts

Hello friends, welcome to Gate Smashers

In today's video we are going to discuss

different types of registers.

Before starting the video, I want to tell you one thing

That computer organization

has always been a tricky subject for students.

Because we discuss hardware and software both in this

And students try to cram these concepts

And because of that they are lacking in this whole subject

But in all the videos I am bringing

In these we'll discuss the concepts one by one in sequential order

With which you will get total clarity

That how actually the hardware and software works.

In the last video we discussed

How we connect registers with the common bus

And how we implement the common bus

with the help of multiplexers

Do check that video once

Because you will get an idea from it

That what we are talking about, about registers or different types of registers

Before that you should know how we connect them

How the circuit actually looks like

Here we are talking about different types of registers

In which we first of all talk about address register

Data register, accumulator, program counter

Instruction register, temporary register, input and output register

Now their size, how big is the size of this register

Generally the registers in our system are 16 bit

Or they can be 8 bit or 32 bit

But generally we use 16 bit registers

Now these registers are basically sequence of bits or flip flops

But how their size matters

how do we measure their size that depends on this concept

So first of all if you talk about memory

we are talking about the memory which is RAM

That is 4096*16

We have taken a very small size so that you will get to know about this concept

So if we talk about memory 4096

So what is 4096

It is number of words

Number of words

if you are talking about a particular memory

If we talk about this memory here

Then how many total number of words we will have.

Total number of words, now how many bits we can store in that word

Means the size of the word

Now I will tell you what this word is

In operating system we generally talk about block

But in computer organization we use this word a lot that is a "word".

Now what is word actually

It is a memory representational unit Means to represent memory

We use word, although we use byte You must have heard about byte

That memory is byte addressable But byte is actually a fixed number

One byte is equal to 8 bits

But today we are using operating system 32 bits, 64 bits

So the size of the word is not limited to 1 byte it can be 2 bytes or 4 bytes

Means multiple bytes can also be a word

if we talk about memory in real life scenario

Then it is word addressable So what is word here

That how many words we can store in memory

That is called the number of words, that is 4096

And how many bits can come in every word

Means total size of that word is 16

And 16 means, bits Which you can call 2 bytes

Means in our example One word is 2 bytes

You can also call it like this Now if we talk about 4096

So 4096 means number of words we have

2 raised to power 12

You can write it as 2 raised to power 12

Because how we will give it numbering like this 0 0 0 0 0

Means 12 number of 0

Then 0 0 0 0 0 0 1

By doing like this at the end 1 1 1 1 1 1

Means continuously 12 "1"

And in this way we will provide an address to all the words

And we have to keep in that word 16 bits

So 16 bits means 2 raised to power 4

You can mention it in this way also

Now we will talk about address register

What is the use of address register With address register

We actually pick up data in memory the words in memory

Now let's say I have to pick up data from a particular address

That address we have to give to memory

That brother pick up the word from this particular location

From this particular value pick up the

instruction from there So how will it happen

For that we have to mention address here

And that address will be in address register

And with address register we will give that address to memory

Memory will decode it

And after decoding it will go to that particular location and fetch the data

This is actually the work of address register

So if we ask you what will be the size of address register

According to this example what will be the size of address

How many number of words we have

12 2 raised to power 12

Means from 0 to 11

So what will be the total number of size

Total size of address register will be 12 bits

Simple how many values are we representing address

2 raised to power 12 means 12 values are represented

So address register will be of how many bits?

12 bits.

Here from 0 0 0 0 to 1 1 1 continuously

Any value can exist between 12 and 1

Then data register, from the name we are getting to know that data register means

Where we store data

Means where we bring data Now what are we putting in data register

And what is the size of data How many bits can come here

How many bits will be in a word.

In a whole location we told the size of a word is 16

So these can be 16 bits So what is the total size of the address

0 to 15 means Total size of data register will be 16

You can ask here in this way

And you should know this Because this is a very basic point

We will use them later Will try to design the computer

And how all these registers are connected to each other

With ALU and how they are connected to each other

We will see that in the next video

So that you can know How we fetch the instructions How ALU executes

How we keep the data temporarily on the way You will know all these points there

But these points will tell you What are the registers

How we measure their size

Accumulator

What is the use of the accumulator here

We use the accumulator To store intermediate data

Means if data comes from ALU

we keep it In the accumulator Means in the intermediate

Like we are converting the input to the output

So if I have to store any particular data for a while

Then we can store that data in the accumulator We picked up the data from memory

After fetching the data from memory We have to give it to ALU

So what can we do before that We can keep it in the accumulator for a while

So what are we keeping in the accumulator

Data, So what is the size of the data

According to this example, 16

So what is the accumulator From 0 to 15 bits Means total number of bits is 16.

Program counter Program counter is basically

we use to store the address of next instruction

Means let's say that our instruction is I1

And I1 instruction is at 1000 address At 1000 number address

So what is program instruction

With our program counter we fetched this instruction

As soon as we fetched this instruction So what is this whole area It is empty

So where is the next instruction Next instruction is at 1001

Which instruction is that I2

So here the program counter that I have

Program counter always points out that location

Where the instruction is.

Not where we picked up the instruction from This is always the next instruction

Where the instruction is It will always store

that particular address

If we talk about this scenario currently

we had already taken out the instruction from 1000

So where is the next instruction In 1001

Means what will be the value of program counter 1001

Means this point is basically telling

Where our instruction is now we picked up from here.

As soon as we picked up the instruction from here

So where is the next instruction

Let's say at 1002

So all these 7 will change to 1002

So wherever your next instruction is

That address is in the program counter

So again what am I saying here Address What are you keeping here Address

the next instruction location or address of that place

And address we have already told

That how many bits are used to represent the address 12

So what is the program counter From 0 to 11 bit Or which you can simply say

12 bits Program counter.

Then instruction register this is main

Because what we have to do actually We have to execute the instructions

What ALU has to do, stored the program, execute that program

So what do we have in memory we discussed in Von Neumann's architecture

Stored memory architecture Where we keep instruction & data in same memory

So what happens is that our memory

in that memory

Instruction is stored Instruction means

let's say the format of instruction you see first

In the format of instruction we have an opcode

And the second is operand

What are the LSB bits showing Operand means data

Opcode is telling What operation you have to perform

Means you have to do addition, subtraction Multiplication

different types of Opcode operations will be here

and where is the data

That will be on operand So let's say if I write here

I write add, and here I wrote 450

So what will happen What does it mean

what instruction we took from there what should we do there

One is addition and 450 is telling Where operand is stored

Means your data is stored in memory But at which location 450 location

So you go to 450 location

And fetch the data from there

the entire format of instruction

Both these things are important That is opcode and operand

Operand from where you have to pick up data

That particular address And what is opcode

What operation you have to perform

But I have written one more thing, i

The last MSB is most significant bit

We keep one bit here Either 0 or 1

0 represents direct address And 1 represents indirect Addressing

We will discuss about this in detail in next video But a little idea

Like we discussed this example according to that

Let's say I wrote add

And here 450

Now here if I have this bit Which is msb If its value is 0

Means Direct address Means you go to 450 location

Whatever data is there pick up that data And give it to accumulator

So what is this thing telling me?

It is telling address where data is there And it is telling

Direct, means as soon as you go there

You will get your data But if its value is 1.

Means what is this?

Indirect Addressing Means you have to go to 450 first When you go to 450

On that location It may be written 1002

Means what is this? Address,

now you have to go to 1002

What will you get by going there?

Address These are different types of addressing modes

Which we will see in detail next

Now what you have to do What we are doing in instruction register

We are storing the whole instruction here

And instruction in our case Again 0 to 15

Means total 16 bits What is operand?

Now I have told you address

that go to 450 location Go to this particular location

So you know the location is 12 bit Because number of words we have

According to our example 4096

So 12 is representing operand value here And the other 3

Because this bit is representing Direct and indirect

So the remaining 3 bits here That is what? Opcode

And what is that opcode? Addition, subtraction Multiplication, division

What you have to do? Which operation You have to perform here?

So this basically is the format of instruction register

And this instruction will come in instruction register

what will be the size of instruction register?

0 to 15

That is 16 bits So in this way

The value of registers The size we measure

Next comes temporary register

Temporary register means The one we use to

store temporary data Again here data is stored

So means 0 to 15 means 16 bits size Then we have input register

Input register is To pick up data from input devices

Means you typed something from keyboard So we pick up data from there

And put it in input register

and give that data to ALU From input register

Or in accumulator so input register It has nothing to do with this

Where does it take input? It takes from input devices So in our case you take it

Simply 8 bits for simplicity

You can increase it That is it has nothing to do with this

the data taken from input devices

And such output register Obviously what we have to represent is output

From where will it pick up data?

It will pick up output register from ALU

Now who has to be given that output?

We have to give that output to output devices Like printer, scanner, monitor

So to give that we use output register

So these are basic registers

Which we use but How is their connectivity?

How do we use this in sequence?

And how is the instruction fetched?

Decoded? How do we convert it in output?

We will see this in next video Here you have just given a basic idea

What are different types of registers?

And how do we measure their sizes?

Thank you.