Two’s Complement - 8.2.3 | 8. Hexadecimal Representation | Computer Organisation and Architecture - Vol 1
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Introduction to Two's Complement

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0:00
Teacher
Teacher

Let's discuss how computers represent negative numbers. One efficient method is called two's complement. Can anyone suggest why we might need a way to represent negative numbers?

Student 1
Student 1

We need to do calculations with negative numbers, like subtraction!

Teacher
Teacher

Exactly! Now, can someone tell me what we know about the binary number system?

Student 2
Student 2

It consists of only 0s and 1s!

Teacher
Teacher

Right! Two's complement allows us to represent both positive and negative numbers using this binary system. This representation helps streamline binary arithmetic. Remember, in two's complement, the most significant bit helps identify the sign of the number.

Student 3
Student 3

So, if the most significant bit is 1, it represents a negative number?

Teacher
Teacher

Correct! Now, let's summarize. Two's complement enables us to work with negative values while maintaining a simple binary system.

Converting to Two's Complement

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Teacher
Teacher

To convert a positive number to its two's complement form, we first find the binary representation. Let’s take 3 as an example. What is its binary representation?

Student 4
Student 4

It's 00000011 for 8 bits!

Teacher
Teacher

Spot on! Next, how do we convert this to its two's complement?

Student 1
Student 1

We flip all the bits to get 11111100, which is the one's complement.

Teacher
Teacher

Exactly! Now what do we do next?

Student 2
Student 2

We add 1 to it!

Teacher
Teacher

Correct, adding 1 gives us 11111101. This binary value represents -3 in two's complement. Remember, this conversion is essential for performing operations with negative numbers.

Two's Complement Arithmetic

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Teacher
Teacher

Now that we know how to convert to two's complement, let's perform some arithmetic with it. What is 5 + (-3)?

Student 3
Student 3

We convert -3 to its two's complement!

Teacher
Teacher

Exactly! What is -3 in two's complement?

Student 1
Student 1

It's 11111101 for -3!

Teacher
Teacher

Great! Now, let’s convert 5 into binary and add it to -3. What's 5 in binary?

Student 2
Student 2

It's 00000101!

Teacher
Teacher

Right! Let's add: 00000101 and 11111101. What do we get?

Student 4
Student 4

That’s 00000000 with a carry out!

Teacher
Teacher

Correct! In this case, adding a positive and negative number returned 0, indicating our operation was accurate.

Understanding Overflow

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Teacher
Teacher

Sometimes when adding in two's complement, we face an issue called overflow. Can anyone explain what that means?

Student 3
Student 3

It happens when the result is too large or too small for the number of bits we have!

Teacher
Teacher

Yes! For example, adding two positive 8-bit numbers could yield a result that requires more than 8 bits. What happens then?

Student 1
Student 1

We ignore the carry out!

Teacher
Teacher

Very good! So if we add two numbers and the signs don’t match but overflow occurs, we need to be aware that the result isn't valid. This understanding is vital for avoiding errors in computations.

Introduction & Overview

Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.

Quick Overview

Two's complement is a binary number representation used for encoding negative integers, allowing for straightforward binary addition and subtraction operations.

Standard

This section explores two's complement, a technique for representing negative integers in binary systems, emphasizing its importance in computing. It discusses the advantages of using two's complement over other methods, including sign-magnitude representation, and explains how to convert positive numbers to negative ones using binary operations such as one's complement and bitwise addition.

Detailed

Two’s Complement

Two's complement is a crucial method used in computer systems to represent negative numbers in binary. Unlike other representations, such as sign-magnitude, which can complicate operations by requiring separate sign handling, two's complement simplifies arithmetic operations. This method utilizes a fixed number of bits to represent both positive and negative integers, allowing binary addition and subtraction without special rules for negative values.

The range of representable integers with two's complement depends on the bit-width: for 8 bits, the range spans from -128 to +127. Understanding how to convert a positive integer to its two's complement negative form involves taking the one's complement (flipping the bits) and adding one to the least significant bit. This conversion is essential for handling arithmetic operations involving negative numbers efficiently.

Additionally, the section delves into examples that illustrate how to perform addition and identify overflow conditions, ensuring that learners can apply these concepts effectively in practical scenarios.

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Audio Book

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Understanding Two's Complement Basics

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So, the similar information I am representing in another number system which is your hexadecimal. Now, you just see what I am saying this is your 8 bit number all 0s to all 1s. So, all 1 in decimal it becomes 255 in hexadecimal it is your FF, FF means 15 F represents 15, 15 × 161 + 15 × 160. So, in that particular case we will get that this is nothing but 255 in decimal.

Detailed Explanation

The two's complement system is a way to represent both positive and negative integers in binary. In an 8-bit binary system, you can use a range from all 0s (00000000) to all 1s (11111111). The maximum positive number you can represent with 8 bits is 255, which, when converted into hexadecimal, is represented as FF (since F = 15, FF = 15 × 16^1 + 15 × 16^0). This highlights how hexadecimal can simplify binary representation.

Examples & Analogies

Think of it like counting in a classroom. You can count students (binary) using hand signals (1s and 0s). When the number of students grows beyond a certain limit (like 255), instead of counting on fingers, you use tokens (hexadecimal) to quickly show how many students are there.

Converting Binary to Hexadecimal

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Now, when we are going to discuss that representation of number in computer or in your binary system or binary digit most of the time we are going to take help of hexadecimal number system because it is having one advantage. Say, when I am going to work with 32 bit number I have to write 32 bits ok all 32 bits 0 or maybe combination of 0s and 1 which is slightly difficult. Similarly when we are going to work with 8 bits we are going to write 8 bits all 0s to all 1.

Detailed Explanation

When working with binary representations, particularly with larger numbers like 32 bits, writing out every single bit can be cumbersome. Instead, hexadecimal provides a more compact form. Each hexadecimal digit corresponds to four binary bits, making it easier and faster to read and write. For instance, a full 32-bit number would require 32 bits written out, but can instead be represented with just 8 hexadecimal characters.

Examples & Analogies

Imagine presenting a long report in a written format. Instead of writing each detail in full, you could summarize the report into a shorter version with bullet points (hexadecimal), making it easier for your audience to grasp the key ideas quickly.

Positive and Negative Number Representation

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So, in that case for hexadecimal representation this very simple, you just see if I am having a 4 bit number then all 0 if I am having then this is your 0 and if it is all 1 you can say that 8 + 4 = 12, 12 + 2 =14, 14 + 1= 15. So, this is your 15 so we need total 16 different symbol 0 to 9 and A to F, F is 16 and A is 10.

Detailed Explanation

In the two's complement format, numbers are represented with a fixed number of bits. In a system that uses 4 bits, the positive numbers (0-15) are represented directly as usual, while the negative numbers are represented by their two's complement forms. Essentially, this means you can go from 0 (0000) to 15 (1111), with A (10) to F (15) filling in the representation for numbers above 9.

Examples & Analogies

Think of a game where scores are tracked from -15 to +15. You can have scores like 0 to 15, but when a player loses, you indicate scores in the negatives. The game has a special way to show negatives using a certain card (two's complement) that has a different color, making it clear when someone is below zero.

The Range of Values in Two's Complement

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So basically what happens? It is basically the maximum number is a 255 or 8 bit representation that 255 is going to represent my -1 now you just count down and go downwards then 554 is going to give me -2, 253 will give me your -3.

Detailed Explanation

In an 8-bit two's complement representation, the range is from -128 to +127. This means that while the maximum positive value is 127 (0111 1111), the minimum negative value is -128 (1000 0000). When counting down from 255, the -1 is represented as the pattern of all 1s (1111 1111) and decreases towards -128.

Examples & Analogies

Imagine a temperature gauge where the midpoint (0 degrees) is balanced. As it extends into negatives (below 0), it counts down further, but once you reach the lowest point (-128), you can't go any lower, just like in the binary system.

Calculating Two's Complement

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So, in two’s complement just I am giving one example just only getting phone numbers now in that particular case what will happen this is the representation if I am having 0 then these are all 0s, + one is simple that magnitude 1, 10, 11 like that if I go for positive 4 then it will be 100 like that and negative number is coming as - 1 is representing as your all 1s then -2 is coming as your all 1 and 0.

Detailed Explanation

To find the two's complement of a binary number, start with the binary representation of the number, invert all bits (change 0s to 1s and vice versa), and then add 1 to the least significant bit (LSB). This method effectively allows representation of negative numbers in binary format.

Examples & Analogies

Consider a clock. When the minute hand points to zero, it means '0' hours. If you want to go back an hour (negative), you could either visually move backwards or calculate the time in reverse using your clock’s mechanism (just like the two's complement method does with binary).

Detecting Overflow in Two's Complement

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So, just I am calculating it just show it now what will happens say when I use - 7 to - 1 should get - 6 and I am getting it. So, this is also correct result, but when I am using - 7 + - 7 what should be my result my result should be 14, but as a result I am getting 2 only.

Detailed Explanation

In two's complement arithmetic, you may encounter an overflow situation when adding two numbers that produce a result outside of the range representable by the allocated bits. If the result of an addition causes the computation to exceed the maximum (e.g., adding two positive numbers gives a negative result) or the minimum, this indicates overflow.

Examples & Analogies

Imagine trying to put more boxes into a truck than it can hold. If you stack boxes up to the point where they start falling off (like your result going beyond the limits), you've exceeded your truck's capacity (overflow) and can't accurately represent how many boxes there actually are anymore.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • Two's Complement: A method for representing negative integers in binary.

  • Overflow: A condition in binary arithmetic when results exceed the available number range.

  • Sign Bit: Indicates whether a binary number is positive (0) or negative (1).

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • To convert +3 into two's complement, we represent it as 00000011. Upon flipping the bits and adding 1, we obtain 11111101, which represents -3.

  • Adding 5 and -3: Convert 5 (00000101) and -3 (11111101) and sum them to yield 00000000.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • To find two's complement, flip and then add, that's the right trend to avoid being sad.

📖 Fascinating Stories

  • Imagine you have 3 apples and want to represent -3. First, you flip your apples (one's complement), then give one away, resulting in -3.

🧠 Other Memory Gems

  • F A A: Flip and Add for calculating Two's Complement.

🎯 Super Acronyms

TCA - Two's Complement Arithmetic

  • Remember to Flip and Add to convert numbers.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Two's Complement

    Definition:

    A binary representation method that allows for negative integer values in computing.

  • Term: One's Complement

    Definition:

    The binary form obtained by flipping all bits in a binary number.

  • Term: Overflow

    Definition:

    A condition that occurs when the result of an arithmetic operation exceeds the ability of the number representation.

  • Term: Binary

    Definition:

    A number system that uses only two symbols: 0 and 1.

  • Term: Sign Bit

    Definition:

    The bit that indicates whether a number is positive or negative in binary representation.