Excess Codes and GREY Code - 9.1.6 | 9. Floating Point Number Representation | Computer Organisation and Architecture - Vol 1
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Understanding Floating Point Representation

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Teacher
Teacher

Today, we'll discuss floating point representation, which is crucial for storing real numbers in computers. Can anyone tell me what the three main components of a floating-point number are?

Student 1
Student 1

Isn't it the sign bit, the exponent, and the significand?

Teacher
Teacher

That's correct! The sign bit indicates if the number is positive or negative. The exponent tells us how large or small the number is, and the significand contains the actual digits of the number. Now, how many bits are typically used for each component in a 32-bit floating point?

Student 2
Student 2

One bit for the sign, eight bits for the exponent, and 23 bits for the significand?

Teacher
Teacher

Exactly! Remember this with the acronym 'S-E-S' for Sign, Exponent, and Significand. Let’s move on to how these components are combined in actual representation.

Biased Exponents and Excess Codes

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Teacher
Teacher

Now, let's explore how we represent exponents using excess codes, also known as biased exponents. Who can explain why we use bias?

Student 3
Student 3

It's to easily handle both positive and negative exponents, right?

Teacher
Teacher

Great insight! For instance, in the IEEE 754 standard, we add 127 as a bias for 8-bit exponents. So, if we want to store an exponent of 20, we actually store 147. Can you figure out how?

Student 4
Student 4

Yes! We just add 127 to the exponent!

Teacher
Teacher

Correct! This concept helps avoid negative numbers in exponents, making calculations simpler. Now, let’s recap: bias helps in simplifying representation. Can you all say it together?

All Students
All Students

Bias simplifies floating point representation!

Accuracy of Floating Point Numbers

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Teacher
Teacher

Moving forward, let’s talk about the accuracy of floating-point numbers. Why do you think having more bits in the significand increases accuracy?

Student 1
Student 1

Because more bits mean we can store more precise values?

Teacher
Teacher

Exactly! With 23 bits in the significand, we can achieve up to 7 decimal places. What happens if we only have 22?

Student 2
Student 2

We might start losing precision, right?

Teacher
Teacher

Correct! If you change the least significant bit, it changes the overall value, leading to potential inaccuracies. Now, remember, precision is key in computing!

GREY Code Minimizing Bit Changes

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Teacher
Teacher

Now, let’s dive into GREY code and how it minimizes the number of changed bits between consecutive numbers. Can someone explain what GREY code is?

Student 3
Student 3

It's a binary numeral system that only changes one bit at a time when going from one number to the next.

Teacher
Teacher

Exactly! This reduces errors in digital operations, particularly in hardware circuits. Why do you think this is important?

Student 4
Student 4

To prevent errors during transitions, which can mess up data processing!

Teacher
Teacher

Yes! Minimizing bit changes ensures that systems remain stable and reliable. So, when working with digital systems, remember GREY code as ' minimizing changes!'

Introduction & Overview

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Quick Overview

This section discusses floating point representation, focusing on excess (biased) codes and GREY code, highlighting their applications and advantages in minimizing errors during numerical transitions.

Standard

The content delves into the concepts of floating-point representation, including the handling of sign bits, biased exponents, and significands, along with the definitions and applications of excess codes. Additionally, GREY code is introduced, which focuses on reducing signal changes between consecutive numbers to minimize error in digital systems. The section also touches upon binary-coded decimal representation and character encoding standards like ASCII and Unicode.

Detailed

Detailed Summary

In this section, we cover the fundamentals of floating-point representations such as excess codes and GREY code, as well as their significance in digital computations.

Key Concepts Covered:

  1. Floating Point Representation: Numbers are stored as a combination of the sign bit, biased exponent, and significand. A typical format for floating-point representation is a 32-bit structure with 1 bit for the sign, 8 bits for the exponent, and 23 bits for the significand.
  2. Excess (Biased) Code: In floating-point representation, the exponent is stored with a bias to simplify the representation of negative numbers. For example, in an 8-bit model, an exponent is often stored by adding a bias (such as 127 for IEEE 754 format). This allows easy representation of both positive and negative exponents.
  3. Accuracy in Floating Point Numbers: Accuracy depends on the bits used in the significand. If 23 bits are used, the precision can extend to about 6-7 decimal places, but can lead to information loss on conversion.
  4. GREY Code: GREY code decreases the number of bit changes required when moving from one number to the next. This variant representation helps minimize errors in digital circuits especially in systems where small errors can lead to larger discrepancies.
  5. Applications of Codes: The section illustrates the applications of both excess code for floating-point numbers and GREY code in digital systems, providing evidence of standardization in representation systems, including ASCII and Unicode for character representation.

Importance:

Understanding excess codes and GREY code is crucial for effective numerical computation and error reduction in various digital systems and ensures accurate representation of data.

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Understanding Excess Codes

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So, if we are using 8 bit numbers then excess will be your excess 128; because to represent negative numbers as well as positive numbers what we do is store the positive number then we subtract something from that particular number to get the exact number.

Detailed Explanation

Excess codes, also known as biased representation, allow us to store both positive and negative numbers effectively. With 8-bit numbers, the excess is set to 128. This means when we want to store a number, we add 128 to it (the bias) before saving it in the system. When we want to retrieve or evaluate the number, we subtract the bias of 128 from what is stored. This method simplifies the handling of both positive and negative values, making operations easier in computing systems.

Examples & Analogies

Think of excess codes like a ticketing system where every ticket has a hidden base price of $128. If someone buys a ticket for $140, the system records it as $12 (because 140 - 128 = 12). If a ticket with a price of $100 is bought, it would show as -28 (because 100 - 128 = -28). This way, the system can manage a range of prices effectively, both above and below $128.

Biased Exponent Explanation

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So, in this representation, it is biased by 128; that means, whatever number we are storing over here that will be that to find out the exact exponent, 127 will be subtracted from that.

Detailed Explanation

In floating point representation, the exponent is stored in a biased form. For an 8-bit exponent, the bias is generally 127. This means if we want to represent an exponent of 20, we store 147 (which is 20 plus the bias of 127). This makes calculations involving exponents manageable, as it allows for both negative and positive exponents while keeping all values stored as positive numbers.

Examples & Analogies

Imagine you are on a team where everyone measures height differently. Instead of asking for your exact height, everyone uses a standard height as a reference point. If your height is 5'10'', you would tell them you're 10 inches above the reference point of 5'0''. This makes it easier to communicate height differences, similar to how biased exponents simplify math with positive and negative numbers.

Normalization in Floating Point Representation

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So, this is the way we are going to do it. So, the mantissa will be stored in your 2’s complement form, exponent will be stored in your biased exponent.

Detailed Explanation

Normalization is an important process in floating point representation. It ensures that the significand (or mantissa) is always stored in a standardized form. Essentially, we represent numbers such that the decimal point is just after the first significant digit. For instance, the number 1.1010001 is used to simplify calculations. The main goal of normalization is to maintain precision while ensuring the system requirements for floating point representation are met.

Examples & Analogies

Imagine a chef following a recipe that requires each ingredient to be measured uniformly. Instead of saying a tablespoon could be 15ml or 16ml depending on how full you fill it, you standardize everything to exactly 15ml. This practice of normalization ensures everyone uses the same measurements, leading to consistent results. In floating point numbers, forbidding variations in how numbers are stored leads to more precise computing.

Understanding GREY Code

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GREY code is consists just to minimize this particular changes of bits when you go from one number to the next number.

Detailed Explanation

GREY code is designed such that only one bit changes at a time as you move from one decimal number to the next. This is particularly useful in digital systems where minimizing errors caused by simultaneous bit changes is crucial. For example, changing the binary representation of 8 to 9 might change three bits, which could cause errors in high-speed circuits. With GREY code, the transition is smoother and less error-prone.

Examples & Analogies

Imagine driving a car where only one gear changes at a time instead of multiple gears shifting all at once. This makes the drive smoother, reducing the chances of stalling or confusion while switching speeds. Similarly, GREY code allows smoother transitions between numbers, reducing potential errors in digital circuits.

Binary Coded Decimal (BCD)

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In binary coded decimal, what we are going to do digit wise we are going to convert to the binary.

Detailed Explanation

Binary Coded Decimal (BCD) is a method to express each decimal digit separately in binary format. For example, the decimal number 12 is represented in BCD as 0001 for '1' and 0010 for '2'. This approach makes calculations involving decimal digits more straightforward in computing. Although it takes more bits to represent numbers as compared to pure binary, BCD allows for simplified digit-wise processing, retaining the familiar decimal structure.

Examples & Analogies

Think of BCD as an old-fashioned filing system where every single paper represents one of your document's digits. Instead of having all your documents mixed together in one messy pile, you organize them meticulously. Number '12' would be two separate files: one for '1' and another for '2'. This method makes it easy to retrieve and work with individual digits, just as BCD helps computers manage decimal digits efficiently.

Definitions & Key Concepts

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

Key Concepts

  • Floating Point Representation: Numbers are stored as a combination of the sign bit, biased exponent, and significand. A typical format for floating-point representation is a 32-bit structure with 1 bit for the sign, 8 bits for the exponent, and 23 bits for the significand.

  • Excess (Biased) Code: In floating-point representation, the exponent is stored with a bias to simplify the representation of negative numbers. For example, in an 8-bit model, an exponent is often stored by adding a bias (such as 127 for IEEE 754 format). This allows easy representation of both positive and negative exponents.

  • Accuracy in Floating Point Numbers: Accuracy depends on the bits used in the significand. If 23 bits are used, the precision can extend to about 6-7 decimal places, but can lead to information loss on conversion.

  • GREY Code: GREY code decreases the number of bit changes required when moving from one number to the next. This variant representation helps minimize errors in digital circuits especially in systems where small errors can lead to larger discrepancies.

  • Applications of Codes: The section illustrates the applications of both excess code for floating-point numbers and GREY code in digital systems, providing evidence of standardization in representation systems, including ASCII and Unicode for character representation.

  • Importance:

  • Understanding excess codes and GREY code is crucial for effective numerical computation and error reduction in various digital systems and ensures accurate representation of data.

Examples & Real-Life Applications

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

Examples

  • Example of floating-point representation: A number like -12.375 could be broken into its components: Sign bit = 1, Exponent = 10001 (with a bias), and the significand would be stored in remaining bits.

  • Example of GREY code: The binary for 1 is '001', for 2 is '010', and across these transitions, changes happen only in one bit instead of two as in regular binary.

Memory Aids

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

🎵 Rhymes Time

  • Floating point's trick to save space,

📖 Fascinating Stories

  • In a world of numbers, a secret was kept—how to stay positive while feeling negative using surprises called excess codes. They allowed positivity by using friendly biases, simplifying the path for all numbers.

🧠 Other Memory Gems

  • Remember 'S-E-S' for Sign bit, Exponent, Significand.

🎯 Super Acronyms

GREY = G=Game play, R=Reduce, E=Errors, Y=Yes! It helps minimize!

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Floating Point Representation

    Definition:

    A method of representing real numbers in computers using a sign bit, exponent, and significand.

  • Term: Excess Code

    Definition:

    A coding method where the exponent is represented by adding a bias to allow for negative exponents.

  • Term: Significand

    Definition:

    The part of a floating-point number that contains its significant digits.

  • Term: Biased Exponent

    Definition:

    An exponent stored in a way that lets both positive and negative values be represented as non-negative.

  • Term: GREY Code

    Definition:

    A binary numeral system that changes only one bit between consecutive values to minimize error.