### Data representation in computer systems реферат

Digital computers store and process information in binary form as digital logic has only two values “1” and “0” or in other words “True or False” or also said as “ON or OFF”. This system is called radix 2. We human generally deal with radix 10 i.e. decimal. As a matter of convenience there are many other representations like Octal (Radix 8), Hexadecimal (Radix 16), Binary coded decimal (BCD), Decimal etc.

Every computer’s CPU has a width measured in terms of bits such as 8 bit CPU, 16 bit CPU, 32 bit CPU etc. Similarly, each memory location can store a fixed number of bits and is called memory width. Given the size of the CPU and Memory, it is for the programmer to handle his data representation. Most of the readers may be knowing that 4 bits form a Nibble, 8 bits form a byte. The word length is defined by the Instruction Set Architecture of the CPU. The word length may be equal to the width of the CPU.

The memory simply stores information as a binary pattern of 1’s and 0’s. It is to be interpreted as what the content of a memory location means. If the CPU is in the Fetch cycle, it interprets the fetched memory content to be instruction and decodes based on Instruction format. In the Execute cycle, the information from memory is considered as data. As a common man using a computer, we think computers handle English or other alphabets, special characters or numbers. A programmer considers memory content to be data types of the programming language he uses. Now recall figure 1.2 and 1.3 of chapter 1 to reinforce your thought that conversion happens from computer user interface to internal representation and storage.

## Data Representation in Computers

Information handled by a computer is classified as instruction and data. A broad overview of the internal representation of the information is illustrated in figure 3.1. No matter whether it is data in a numeric or non-numeric form or integer, everything is internally represented in Binary. It is up to the programmer to handle the interpretation of the binary pattern and this interpretation is called Data Representation. These data representation schemes are all standardized by international organizations.

Choice of Data representation to be used in a computer is decided by

• The number types to be represented (integer, real, signed, unsigned, etc.)
• Range of values likely to be represented (maximum and minimum to be represented)
• The Precision of the numbers i.e. maximum accuracy of representation (floating point single precision, double precision etc)
• If non-numeric i.e. character, character representation standard to be chosen. ASCII, EBCDIC, UTF are examples of character representation standards.
• The hardware support in terms of word width, instruction. Before we go into the details, let us take an example of interpretation. Say a byte in Memory has value “0011 0001”. Although there exists a possibility of so many interpretations as in figure 3.2, the program has only one interpretation as decided by the programmer and declared in the program. ## Fixed point Number Representation

Fixed point numbers are also known as whole numbers or Integers. The number of bits used in representing the integer also implies the maximum number that can be represented in the system hardware. However for the efficiency of storage and operations, one may choose to represent the integer with one Byte, two Bytes, Four bytes or more. This space allocation is translated from the definition used by the programmer while defining a variable as integer short or long and the Instruction Set Architecture.

In addition to the bit length definition for integers, we also have a choice to represent them as below:

• Unsigned Integer: A positive number including zero can be represented in this format. All the allotted bits are utilised in defining the number. So if one is using 8 bits to represent the unsigned integer, the range of values that can be represented is 28 i.e. “0” to “255”. If 16 bits are used for representing then the range is 216 i.e. “0 to 65535”.
• Signed Integer: In this format negative numbers, zero, and positive numbers can be represented. A sign bit indicates the magnitude direction as positive or negative. There are three possible representations for signed integer and these are Sign Magnitude format, 1’s Compliment format and 2’s Complement format.

Signed Integer – Sign Magnitude format: Most Significant Bit (MSB) is reserved for indicating the direction of the magnitude (value). A “0” on MSB means a positive number and a “1” on MSB means a negative number. If n bits are used for representation, n-1 bits indicate the absolute value of the number. Examples for n=8:

Examples for n=8:

0010 1111 = + 47 Decimal (Positive number)

1010 1111 = – 47 Decimal (Negative Number)

0111 1110 = +126 (Positive number)

1111 1110 = -126 (Negative Number)

0000 0000 = + 0 (Postive Number)

1000 0000 = – 0 (Negative Number)

Although this method is easy to understand, Sign Magnitude representation has several shortcomings like

• Zero can be represented in two ways causing redundancy and confusion.
• The total range for magnitude representation is limited to 2n-1, although n bits were accounted.
• The separate sign bit makes the addition and subtraction more complicated. Also, comparing two numbers is not straightforward.

Signed Integer – 1’s Complement format: In this format too, MSB is reserved as the sign bit. But the difference is in representing the Magnitude part of the value for negative numbers (magnitude) is inversed and hence called 1’s Complement form. The positive numbers are represented as it is in binary. Let us see some examples to better our understanding.

Examples for n=8:

0010 1111 = + 47 Decimal (Positive number)

1101 0000 = – 47 Decimal (Negative Number)

0111 1110 = +126 (Positive number)

1000 0001 = -126 (Negative Number)

0000 0000 = + 0 (Postive Number)

1111 1111 = – 0 (Negative Number)

## Converting a given binary number to its 2’s complement form

Step 1. -x = x’ + 1 where x’ is the one’s complement of x.

Step 2 Extend the data width of the number, fill up with sign extension i.e. MSB bit is used to fill the bits.

Example: -47 decimal over 8bit representation

```Binary equivalent of + 47 is      0010 1111
Binary equivalent of - 47 is      1010 1111 (Sign Magnitude Form)
1's complement equivalent is      1101 0000
2’s complement equivalent is      1101 0001
```

As you can see zero is not getting represented with redundancy. There is only one way of representing zero. The other problem of the complexity of the arithmetic operation is also eliminated in 2’s complement representation. Subtraction is done as Addition.

More exercises on number conversion are left to the self-interest of readers.

## Floating Point Number system

The maximum number at best represented as a whole number is 2n. In the Scientific world, we do come across numbers like Mass of an Electron is 9.10939 x 10-31 Kg. Velocity of light is 2.99792458 x 108 m/s. Imagine to write the number in a piece of paper without exponent and converting into binary for computer representation. Sure you are tired!!. It makes no sense to write a number in non- readable form or non- processible form. Hence we write such large or small numbers using exponent and mantissa. This is said to be Floating Point representation or real number representation. he real number system could have infinite values between 0 and 1.

Representation in computer

Unlike the two’s complement representation for integer numbers, Floating Point number uses Sign and Magnitude representation for both mantissa and exponent. In the number 9.10939 x 1031, in decimal form, +31 is Exponent, 9.10939 is known as Fraction. Mantissa, Significand and fraction are synonymously used terms. In the computer, the representation is binary and the binary point is not fixed. For example, a number, say, 23.345 can be written as 2.3345 x 101 or 0.23345 x 102 or 2334.5 x 10-2. The representation 2.3345 x 101 is said to be in normalised form.

Floating-point numbers usually use multiple words in memory as we need to allot a sign bit, few bits for exponent and many bits for mantissa. There are standards for such allocation which we will see sooner.

## IEEE 754 Floating Point Representation

We have two standards known as Single Precision and Double Precision from IEEE. These standards enable portability among different computers. Figure 3.3 picturizes Single precision while figure 3.4 picturizes double precision. Single Precision uses 32bit format while double precision is 64 bits word length. As the name suggests double precision can represent fractions with larger accuracy. In both the cases, MSB is sign bit for the mantissa part, followed by Exponent and Mantissa. The exponent part has its sign bit. It is to be noted that in Single Precision, we can represent an exponent in the range -127 to +127. It is possible as a result of arithmetic operations the resulting exponent may not fit in. This situation is called overflow in the case of positive exponent and underflow in the case of negative exponent. The Double Precision format has 11 bits for exponent meaning a number as large as -1023 to 1023 can be represented. The programmer has to make a choice between Single Precision and Double Precision declaration using his knowledge about the data being handled. The Floating Point operations on the regular CPU is very very slow. Generally, a special purpose CPU known as Co-processor is used. This Co-processor works in tandem with the main CPU. The programmer should be using the float declaration only if his data is in real number form. Float declaration is not to be used generously.

## Decimal Numbers Representation

Decimal numbers (radix 10) are represented and processed in the system with the support of additional hardware. We deal with numbers in decimal format in everyday life. Some machines implement decimal arithmetic too, like floating-point arithmetic hardware. In such a case, the CPU uses decimal numbers in BCD (binary coded decimal) form and does BCD arithmetic operation. BCD operates on radix 10. This hardware operates without conversion to pure binary. It uses a nibble to represent a number in packed BCD form. BCD operations require not only special hardware but also decimal instruction set.

## Exceptions and Error Detection

All of us know that when we do arithmetic operations, we get answers which have more digits than the operands (Ex: 8 x 2= 16). This happens in computer arithmetic operations too. When the result size exceeds the allotted size of the variable or the register, it becomes an error and exception. The exception conditions associated with numbers and number operations are Overflow, Underflow, Truncation, Rounding and Multiple Precision. These are detected by the associated hardware in arithmetic Unit. These exceptions apply to both Fixed Point and Floating Point operations. Each of these exceptional conditions has a flag bit assigned in the Processor Status Word (PSW). We may discuss more in detail in the later chapters.

## Character Representation

Another data type is non-numeric and is largely character sets. We use a human-understandable character set to communicate with computer i.e. for both input and output. Standard character sets like EBCDIC and ASCII are chosen to represent alphabets, numbers and special characters. Nowadays Unicode standard is also in use for non-English language like Chinese, Hindi, Spanish, etc. These codes are accessible and available on the internet. Interested readers may access and learn more.

Computers represent data
using 0’s and 1’s, also known as binary
numbers. Why do computers use binary notation instead of the more
familiar decimal notation (using digits 0-9) that people use? Each
digit, whether binary or decimal, must be represented by a voltage in
the computer’s circuitry. It is easy to build circuits that
discriminate between two voltages. We could call these voltages “on”
and “off.” It is much harder, though not impossible, to
build circuits to discriminate reliably among ten different voltages.

 Reading Sequence: Parsons/Oja, Chapter 1-Section C. Learning Goal: Knowledge of the basics of computer hardware and binary notation. 1.3.1 Bits and Bytes. Learning Goal: Knowledge of how data is represented using binary digits of 0’s and 1’s. Also, learn about how data storage capacity is described using typical units of measure used over the years. 1.3.2 Number Systems. Learning Goal: Knowledge of numbering systems used to represent data in computing.
 Assessments: Multiple-Choice Quiz 3

## 1.3.1 Bits and Bytes

• Data
Representation Using Binary Digits

• Increasing
Need for Bytes

## Data Representation Using Binary Digits

A piece of data, such as an
alphabet letter, may be represented using a sequence of binary
digits- 0’s and 1’s. There are several types of codes used to
represent character data. For example, using extended ASCII (America
Standard Code for Information Interchange) code, the alphabet letter
“a” can be represented using a series of eight binary
digits, “01100001.” Each binary digit is called a bit.
And, eight bits is one
byte
.
Extended ASCII code uses eight bits (or one byte) to represent input
characters. Below are binary representations of characters in
extended ASCII code. Figure 1
ASCII code

All data, including audio, visual, and program instruction data can
be represented and stored using a sequence of binary digits, or a
sequence of bytes. Recall that a file is a collection of data. In
some files, the bits of data directly encode individual letters,
numbers, and punctuation symbols that make up words and sentences. In
other files such as an image file, the bits of data need to be
computed in order for them to transform to images that we can
interpret.

Most applications such as Microsoft Word or PowerPoint encode
information in specialized ways that are not readable by humans.
Thus, even though Microsoft Word is often used to edit text, a Word
document cannot be properly displayed by a simple text editor like
Notepad because the document includes information in a format
specific to Microsoft Word. Therefore, it must be opened by Microsoft
Word to be read. Some files have a header section that indicates
which format was used to encode the data in order to allow the
computer to reassemble the binary data back into the human-readable
form of the document.

## Increasing Need for Bytes

In the late 1970s and early 1980s, inexpensive personal computers
were manufactured for the first time, and soon a large consumer
market developed. At first small amounts of memory such as thousands
of bytes were all that was needed to handle the simple spreadsheet
and word processing tasks. But, before long, users wanted software to
allow them to do more tasks such as creating drawings and generating
complex page layouts. As consumer demand grew, computing requirements
also grew. This demand led to new developments that expanded memory
capacities. By the mid 1980s, memory was up to millions of bytes.
Today, office and home computers often have billions of bytes in
memory capacity. Memory for data-intensive systems, such as the
Geographic Information System (GIS), require trillions of bytes.
Below is a chart illustrating the storage capacity over the years
since the 1970s with their associated prefix and abbreviation.

 Decade 1970s 1980s 1990s 2000s Order of magnitude in Storage capacity Thousands Millions Billions Trillions Prefix Kilo (103) Mega (106) Giga (109) Tera (1012) Abbreviation K M G T

the form of both data and programs that act on that data can be
stored. Corresponding to the growth in storage capacity, memory
capacity is also increasing. Moreover, memory technologies are
getting smaller, lighter, and faster, for about the same price. You
unit of this course.

## 1. Introduction

• Computers are classified according to functionality, physical size and purpose.
• Functionality, Computers could be analog, digital or hybrid. Digital computers process data that is in discrete form whereas analog computers process data that is continuous in nature. Hybrid computers on the other hand can process data that is both discrete and continuous.
• In digital computers, the user input is first converted and transmitted as electrical pulses that can be represented by two unique states ON and OFF. The ON state may be represented by a “1” and the off state by a “0”.The sequence of ON’S and OFF’S forms the electrical signals that the computer can understand.
• A digital signal rises suddenly to a peak voltage of +1 for some time then suddenly drops -1 level on the other hand an analog signal rises to +1 and then drops to -1 in a continuous version.
• Although the two graphs look different in their appearance, notice that they repeat themselves at equal time intervals. Electrical signals or waveforms of this nature are said to be periodic.Generally,a periodic wave representing a signal can be described using the following parameters
• Amplitude(A)
• Frequency(f)
• periodic time(T)
• Amplitude (A): this is the maximum displacement that the waveform of an electric signal can attain.
• Frequency (f): is the number of cycles made by a signal in one second. It is measured in hertz.1hert is equivalent to 1 cycle/second.
• Periodic time (T): the time taken by a signal to complete one cycle is called periodic time. Periodic time is given by the formula T=1/f, where f is the frequency of the wave.
• When a digital signal is to be sent over analog telephone lines e.g. e-mail, it has to be converted to analog signal. This is done by connecting a device called a modem to the digital computer. This process of converting a digital signal to an analog signal is known as modulation. On the receiving end, the incoming analog signal is converted back to digital form in a process known as demodulation.

## 2. concepts of data representation in digital computers

• Data and instructions cannot be entered and processed directly into computers using human language. Any type of data be it numbers, letters, special symbols, sound or pictures must first be converted into machine-readable form i.e. binary form. Due to this reason, it is important to understand how a computer together with its peripheral devices handles data in its electronic circuits, on magnetic media and in optical devices.

Data representation in digital circuits

• Electronic components, such as microprocessor, are made up of millions of electronic circuits. The availability of high voltage(on) in these circuits is interpreted as ‘1’ while a low voltage (off) is interpreted as ‘0’.This concept can be compared to switching on and off an electric circuit. When the switch is closed the high voltage in the circuit causes the bulb to light (‘1’ state).on the other hand when the switch is open, the bulb goes off (‘0’ state). This forms a basis for describing data representation in digital computers using the binary number system.

Data representation on magnetic media

• The laser beam reflected from the land is interpreted, as 1.The laser entering the pot is not reflected. This is interpreted as 0.The reflected pattern of light from the rotating disk falls on a receiving photoelectric detector that transforms the patterns into digital form.The presence of a magnetic field in one direction on magnetic media is interpreted as 1; while the field in the opposite direction is interpreted as “0”.Magnetic technology is mostly used on storage devices that are coated with special magnetic materials such as iron oxide. Data is written on the media by arranging the magnetic dipoles of some iron oxide particles to face in the same direction and some others in the opposite direction

Data representation on optical media

In optical devices, the presence of light is interpreted as ‘1’ while its absence is interpreted as ‘0’.Optical devices use this technology to read or store data. Take example of a CD-ROM, if the shiny surface is placed under a powerful microscope, the surface is observed to have very tiny holes called pits. The areas that do not have pits are called land.

## Reason for use of binary system in computers

• It has proved difficult to develop devices that can understand natural language directly due to the complexity of natural languages. However, it is easier to construct electric circuits based on the binary or ON and OFF logic. All forms of data can be represented in binary system format. Other reasons for the use of binary are that digital devices are more reliable, small and use less energy as compared to analog devices.

Bits, bytes, nibble and word

• The terms bits, bytes, nibble and word are used widely in reference to computer memory and data size.
• Bits: can be defined as either a binary, which can be 0, or 1.It is the basic unit of data or information in digital computers.
• Byte: a group of bits (8 bits) used to represent a character. A byte is considered as the basic unit of measuring memory size in computer.
• A nibble: is half a byte, which is usually a grouping of 4 bytes.
• Word: two or more bits make a word. The term word length is used as the measure of the number of bits in each word. For example, a word can have a length of 16 bits, 32 bits, 64 bits etc.

## Types of data representation

• Computers not only process numbers, letters and special symbols but also complex types of data such as sound and pictures. However, these complex types of data take a lot of memory and processor time when coded in binary form.
• This limitation necessitates the need to develop better ways of handling long streams of binary digits.
• Higher number systems are used in computing to reduce these streams of binary digits into manageable form. This helps to improve the processing speed and optimize memory usage.

Number systems and their representation

• A number system is a set of symbols used to represent values derived from a common base or radix.
• As far as computers are concerned, number systems can be classified into two major categories:
• decimal number system
• binary number system
• octal number system

Decimal number system

• The term decimal is derived from a Latin prefix deci, which means ten. Decimal number system has ten digits ranging from 0-9. Because this system has ten digits; it is also called a base ten number system or denary number system.
• A decimal number should always be written with a subscript 10 e.g. X10
• But since this is the most widely used number system in the world, the subscript is usually understood and ignored in written work. However ,when many number systems are considered together, the subscript must always be put so as to differentiate the number systems.
• The magnitude of a number can be considered using these parameters.
• Absolute value
• Place value or positional value
• Base value
• The absolute value is the magnitude of a digit in a number. for example the digit 5 in 7458 has an absolute value of 5 according to its value in the number line.
• The place value of a digit in a number refers to the position of the digit in that number i.e. whether; tens, hundreds, thousands etc.
• The total value of a number is the sum of the place value of each digit making the number.
• The base value of a number also k known as the radix, depends on the type of the number systems that is being used .The value of any number depends on the radix. for example the number 10010 is not equivalent to 1002.

## Binary number system

It uses two digits namely, 1 and 0 to represent numbers. unlike in decimal numbers where the place value goes up in factors of ten, in binary system, the place values increase by the factor of 2.binary numbers are written as X2.consider a binary number such as 10112.The right most digit has a place value of 1×20 while the left most has a place value of 1×23.

Octal number system

Consists of eight digits ranging from 0-7.the place value of octal numbers goes up in factors of eight from right to left.

This is a base 16 number system that consists of sixteen digits ranging from 0-9 and letters A-F where A is equivalent to 10,B to 11 up to F which is equivalent to 15 in base ten system. The place value of hexadecimal numbers goes up in factors of sixteen.

• A hexadecimal number can be denoted using 16 as a subscript or capital letter H to the right of the number .For example, 94B can be written as 94B16 or 94BH.

Further conversion of numbers from one number system to another

• To convert numbers from one system to another. the following conversions will be considered.
• Converting between binary and decimal numbers.
• Converting octal numbers to decimal and binary form.
• Converting hexadecimal numbers to decimal and binary form.
1. a) Conversion between binary and decimal number
2. Converting binary numbers to decimal numbers
• To convert a binary number to a decimal number, we proceed as follows:
• First, write the place values starting from the right hand side.
• Write each digit under its place value.
• Multiply each digit by its corresponding place value.
• Add up the products. The answer will be the decimal number in base ten.

EXAMPLE

Convert 1011012 to base 10(or decimal) number

 Place value 25 24 23 22 21 20 Binary digits 1 0 1 1 0 1

Multiply each digit by its place value

N10=(1*25) +(0*24)+(1*23)+(1*22)+(0*21)+(1*20)

N10=32+0+8+4+0+1

=4510

32*1=32

16*0=0

8*1=8 4*1=4

2*0=0

1*1=1

=4510

NB: remember to indicate the base subscript since it is the value that distinguishes the different systems.

## Teksti

• The binary equivalent of the fractional part is extracted from the products by reading the respective integral digits from the top downwards as shown by the arrow next page.
• Combine the two parts together to set the binary equivalent.

Convert 0.37510 into binary form

0.375×2=0.750

0.750×2=1.500

0.500×2=1.000 (fraction becomes zero)

Therefore 0.37510=0.0112

NB: When converting a real number from binary to decimal, work out the integral part and the fractional parts separately then combine them.

Example

Convert 11.0112 to a decimal number.

Solution

Convert the integral and the fractional parts separately then add them up.

2×1= 2.000

1×1= +1.000

3.00010

 Weight 21 20 . 2-1 2-2 2-3 Binary digit 1 1 . 0 1 1 Values in base 10 2 1 . 0 0.25 0.125

0.50×0 =0.000

0.25×1 =0.250

0.125×1=+0.125

0.37510

3.00010+0.37510= 3.37510

Thus 11.0112=3.37510

1. iv) Converting a decimal fraction to binary

Divide the integral part continuously by 2.For the fractional part, proceed as follows:

Multiply the fractional part by 2 and note down the product

• Take the fractional part of the immediate product and multiply it by 2 again.
• Continue this process until the fractional part of the subsequent product is 0 or starts to repeat itself.

## Teksti

• The following examples illustrate how to convert hexadecimal number to a decimal numberExample

Convert octal number 3218 to its binary equivalent

Solution

Working from left to the right, each octal number is represented using three digits and then combined we get the final binary equivalent. Therefore:

3=0112

2=0102

1=0012

Combining the three from left to right

3218 =0110100012

Converting binary numbers to hexadecimal numbers

• To convert binary numbers to their binary equivalents, simply group the digits of the binary number into groups of four from right to left e.g. 11010001.The next step is to write the hexadecimal equivalent of each group e.g.

1101- D

0001- 1

The equivalent of 11010001 is D1H or D116

Converting hexadecimal numbers to decimal and binary numbers.

Converting hexadecimal numbers to decimal number

• To convert hexadecimal number to base 10 equivalent we proceed as follows:
1. First, write the place values starting from the right hand side.
2. If a digit is a letter such as ‘A’ write its decimal equivalent
• Multiply each hexadecimal digit with its corresponding place value and then add the products

The binary equivalent of the fractional part is extracted from the products by reading the respective integral digits from the top downwards as shown by the arrow next pag

• Combine the two parts together to set the binary equivalent.

Convert 0.37510 into binary form

0.375×2=0.750

0.750×2=1.500

0.500×2=1.000 (fraction becomes zero)

Therefore 0.37510=0.0112

Converting octal numbers to decimal and binary numbers

Converting octal numbers to decimal numbers

• To convert a base 8 number to its decimal equivalent we use the same method as we did with binary numbers. However, it is important to note that the maximum absolute value of a octal digit is 7.For example 982 Is not a valid octal number because digit 9 is not an octal digit, but 7368 is valid because all the digits are in the range 0-7.Example shows how to convert an octal number to a decimal number.

Example 1.13

Convert 5128 to its base 10 equivalent

Solution

 Place value 82 81 80 64 8 1 Octal digit 5 1 2

Write each number under its place value as shown below

Multiply each number by its place value.

N10=(5 x 82)+(1 x 81 )+(2 x 80 )

=(5 x 64)+8+2

=320+8+2

N10=33010

64 x 5=320

8 x 1= 8

1 x 2=+ 2

330

Therefore5128 =33010

Converting octal numbers to binary numbers

• To convert an octal number to binary, each digit is represented by three binary digits because the maximum octal digit i.e. 7 can be represented with a maximum of seven digits. See table:
 Octal digit Binary equivalents 0 000 1 001 2 010 3 011 4 100 5 101 6 110 7 111

## Teksti

Example

Convert the hexadecimal number 11116 to its binary equivalent.

Solution

Place each number under its place value.

256 x1= 256

16 x 1 = 16

1 x 1= + 1

273

Therefore 11116 =27310

Example

Convert octal number 3218 to its binary equivalent

Solution

Working from left to the right, each octal number is represented using three digits and then combined we get the final binary equivalent. Therefore:

3=0112

2=0102

1=0012

Combining the three from left to right

3218 =0110100012

Converting binary numbers to hexadecimal numbers

To convert binary numbers to their binary equivalents, simply group the digits of the binary number into groups of four from right to left e.g. 11010001.The next step is to write the hexadecimal equivalent of each group e.g.

1101- D

0001- 1

The equivalent of 11010001 is D1H or D116

Converting hexadecimal numbers to decimal and binary numbers.

Converting hexadecimal numbers to decimal number

To convert hexadecimal number to base 10 equivalent we proceed as follows:

First, write the place values starting from the right hand side.

1. If a digit is a letter such as ‘A’ write its decimal equivalent
• Multiply each hexadecimal digit with its corresponding place value and then add the products
• The following examples illustrate how to convert hexadecimal number to a decimal number

Example

Convert the hexadecimal number 11116 to its binary equivalent

Solution

Place each number under its place value.

256 x1= 256

16 x 1 = 16

1 x 1= + 1

273

Therefore 11116 =27310

## Converting hexadecimal numbers to binary numbers

• Since F is equivalent to a binary number11112 the hexadecimal number are therefore represented using4 digits as shown in the table below
 Hexadecimal digit Decimal equivalent Binary equivalent 00 00 0000 01 01 0001 02 02 0010 03 03 0011 04 04 0100 05 05 0101 06 06 0110 07 07 0111 08 08 1000 09 09 1001 A 10 1010 B 11 1011 C 12 1100 D 13 1101 E 14 1110 F 15 1111

The simplest method of converting a hexadecimal number to binary is to express each hexadecimal digit as a four bit binary digit number and then arranging the group according to their corresponding positions as shown in example

Example 1

Convert 32116

 Hexadecimal digit 3 2 1 Binary equivalent 0011 0010 0001

Combining the three sets of bits, we get 0011001000012

32116 = 0011001000012

Example 2

Convert 5E616 into binary

 5 E 6 Binary equivalent 0101 1110 0110

5E616 = 0101111001102

## Symbolic representation using coding schemes

• In computing, a single character such as a letter, a number or a symbol is represented by a group of bits. The number of bits per character depends on the coding scheme used.
• The most common coding schemes are:
• Binary Coded Decimal (BCD),
• Extended Binary Coded Decimal Interchange Code (EBCDIC) and
• American Standard Code for Information Interchange (ASCII).

Binary Coded Decimal

• Binary Coded Decimal is a 4-bit code used to represent numeric data only. For example, a number like 9 can be represented using Binary Coded Decimal as 10012 .
• Binary Coded Decimal is mostly used in simple electronic devices like calculators and microwaves. This is because it makes it easier to process and display individual numbers on their Liquid Crystal Display (LCD) screens.
• A standard Binary Coded Decimal, an enhanced format of Binary Coded Decimal, is a 6-bit representation scheme which can represent non-numeric characters. This allows 64 characters to be represented. For letter A can be represented as 1100012 using standard Binary Coded Decimal

Extended Binary Coded Decimal Interchange code (EBCDIC)

• Extended Binary Coded Decimal Interchange code (EBCDIC) is an 8-bit character-coding scheme used primarily on IBM computers. A total of 256 (28) characters can be coded using this scheme. For example, the symbolic representation of letter A using Extended Binary Coded Decimal Interchange code is 110000012.

American standard code for information interchange (ASCII)

• American standard code for information interchange (ASCII) is a 7-bit code, which means that only 128 characters i.e. 27 can be represented. However, manufactures have added an eight bit to this coding scheme, which can now provide for 256 characters.
• This 8-bit coding scheme is referred to as an 8-bit American standard code for information interchange. The symbolic representation of letter A using this scheme is 10000012..

## Binary arithmetic operations

• In mathematics, the four basic arithmetic operations applied on numbers are addition, subtraction, multiplications and division.
• In computers, the same operations are performed inside the central processing unit by the arithmetic and logic unit (ALU). However, the arithmetic and logic unit cannot perform binary subtractions directly. It performs binary subtractions using a process known as For multiplication and division, the arithmetic and logic unit uses a method called shifting before adding the bits.

Representation of signed binary numbers

• In computer technology, there are three common ways of representing a signed binary number.
1. Prefixing an extra sign bit to a binary number.
2. Using ones compliment.
3. Using twos compliment.

Prefixing an extra sign bit to a binary number

• In decimal numbers, a signed number has a prefix “+” for a positive number e.g. +2710 and “-“ for a negative number e.g.27
• However, in binary, a negative number may be represented by prefixing a digit 1 to the number while a positive number may be represented by prefixing a digit 0. For example, the 7-bit binary equivalent of 127 is 11111112. To indicate that it is positive, we add an extra bit (0) to the left of the number i.e. (0)11111112.
• To indicate that it is negative number we add an extra bit (1) i.e. (1)11111112.
• The problem of using this method is that the zero can be represented in two ways i.e.(0)00000002 and (1)00000002.

## Ones compliment

• The term compliment refers to a part which together with another makes up a whole. For example in geometry two complimentary angle (900).
• The idea of compliment is used to address the problem of signed numbers i.e. positive and negative.
• In decimal numbers (0 to 9), we talk of nine’s compliment. For example the nines compliment
• Of 9 is 0, that of 5 is 4 while 3 is 6.
• However, in binary numbers, the ones compliment is the bitwise NOT applied to the number. Bitwise NOT is a unary operator (operation on only one operand) that performs logical negation on each bit. For example the bitwise NOT of 11002 is 00112e.
• 0s are negated to 1s while 1s are negated to 0s.

Twos compliment

• Twos compliment, equivalent to tens compliment in decimal numbers, is the most popular way of representing negative numbers in computer systems. The advantages of using this method are:
1. There are no two ways of representing a zero as in the case with other two methods.
2. Effective addition and subtraction can be done even with numbers that are represented with a sign bit without a need for circuitries to examine the sign of an operand.
• The twos compliment of a number is obtained by getting the ones compliment then adding a 1. For example, to get the twos compliment of a decimal number 4510,
• First convert it to its binary equivalent then find its ones compliment. Add a 1 to ones compliment i.e.

4510=001011012

Bitwise NOT (00101101) =11010010

Two’s compliment = 110100102+12

= 110100112

The five possible additions in binary are

1. 0 + 0 = 0
2. 0+ 12 = 12
3. 12 + 0 = 12
4. 12 + 12 = 102 (read as 0, carry 1)
5. 12 + 12 + 12 = 112 (read as 1, carry 1)

Example 1

Find the sum of 1112 + 0112

Solution

Arrange the bits vertically. 111

Working from the right to the left, we proceed as follows: + 011

Step 1 12 + 12 = 102, (write down 0 and carry 1) 10102

Step 2 12 + 12 + 12 = 112, (add and carry over digit to 1 + 1 in order to get 1 + 1

+1. From the sum, write down digit one the carry

Forward)

Step 3 12 + 12 + 02 = 102, (add the carry over digit to 1 + 0 in order to get

1 + 1 + 0.since this is the last step, write down 10)

Therefore 1112 + 0112 = 10102

This can be summarized in the table

 1st number 1 1 1 2nd number 0 1 1 Carry digit – 1 1 sum 10 1 0

Example 2

101102

10112

+ 1112

Solution

Add the first two numbers and then add the sum to the third number a follows:

Step 1 Step 2

101102 1000012

+ 10112 + 1112

1000012 1010002

## Binary subtraction

Direct subtraction

The four possible subtractions in binary are:

1. 0 – 0 = 0
2. 12 – 0 = 12
3. 12 – 12 = 0
4. 102 – 12 = 12 ( borrow 1 from the next most significant digit to make 0 become 102,

hence 102 – 12 = 12)

Subraction using ones compliment

The main purpose of using ones compliment in computers is to perform binary subtraction. For example to get the difference in 5 – 3, using the ones compliment, we proceed as follows:

1. Rewrite the problem as 5 + (-3) to show that he computer binary subtraction by adding the binary equivalent of 5 to ones compliment of 3.
2. Convert the absolute value of 3 into 8-bits equivalent i.e. 000000112.
3. Take the ones compliment of 000000112e. 111111002 which is the binary representation of -310.
4. Add the binary equivalent of 5 to ones compliment of 3 i.e.

00000101

+ 11111000

(1)00000001

## Subtraction using twos compliments.

Like in ones compliment, the twos compliment of a number is obtained by negating a positive number to is negative counterpart. For example to get the difference in 5-3, using twos compliment, we proceed as follow:

1. rewrite the problem as 5 + (-3)
2. Convert the absolute value of 3 into 8-bit binary equivalent i.e. 00000011.
3. Take the ones compliment of 00000011 i.e. 11111100.
4. add a 1 to the ones compliment i.e. 11111100 to get 11111101
5. add he binary equivalent of 5 to the twos compliment of 3 i.e.

00000101

+ 11111001

(1)00000010 Ignoring the overflow bit, the resulting number is 00000010, which is directly read as a binary equivalent of +2.

Example

Using twos compliment

3110 – 1710 in binary form.

Solution

1710 in binary 00010001

1’s compliment 11101110

2’s compliment 11101111

3110 = 000111112

00011111 + 11101111 = (1)000011102

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A computer uses a fixed number of bits to represent a piece of data which could be a number, a character, image, sound, video, etc. Data representation is the method used internally to represent data in a computer. Let us see how various types of data can be represented in computer memory.

Before discussing data representation of numbers, let us see what a number system is.

## Number Systems

Number systems are the technique to represent numbers in the computer system architecture, every value that you are saving or getting into/from computer memory has a defined number system.

A number is a mathematical object used to count, label, and measure. A number system is a systematic way to represent numbers. The number system we use in our day-to-day life is the decimal number system that uses 10 symbols or digits.

The number 289 is pronounced as two hundred and eighty-nine and it consists of the symbols 2, 8, and 9. Similarly, there are other number systems. Each has its own symbols and method for constructing a number.

A number system has a unique base, which depends upon the number of symbols. The number of symbols used in a number system is called the base or radix of a number system.

Let us discuss some of the number systems. Computer architecture supports the following number systems:

1. Binary Number System
2. Octal Number System
3. Decimal Number System ### Binary Number System

A Binary number system has only two digits that are 0 and 1. Every number (value) represents 0 and 1 in this number system. The base of the binary number system is 2 because it has only two digits.

### Octal Number System

The octal number system has only eight (8) digits from 0 to 7. Every number (value) represents with 0,1,2,3,4,5,6 and 7 in this number system. The base of the octal number system is 8, because it has only 8 digits.

### Decimal Number System

The decimal number system has only ten (10) digits from 0 to 9. Every number (value) represents with 0,1,2,3,4,5,6, 7,8 and 9 in this number system. The base of decimal number system is 10, because it has only 10 digits.

A Hexadecimal number system has sixteen (16) alphanumeric values from 0 to 9 and A to F. Every number (value) represents with 0,1,2,3,4,5,6, 7,8,9,A,B,C,D,E and F in this number system. The base of the hexadecimal number system is 16, because it has 16 alphanumeric values.

Here A is 10, B is 11, C is 12, D is 13, E is 14 and F is 15.

## Data Representation of Characters

There are different methods to represent characters. Some of them are discussed below:

1. ASCII
2. EBCDIC
3. ISCH
4. Unicode ### ASCII

The code called ASCII (pronounced ‘􀀏’.S-key”), which stands for American Standard Code for Information Interchange, uses 7 bits to represent each character in computer memory. The ASCII representation has been adopted as a standard by the U.S. government and is widely accepted.

A unique integer number is assigned to each character. This number called ASCII code of that character is converted into binary for storing in memory. For example, the ASCII code of A is 65, its binary equivalent in 7-bit is 1000001.

Since there are exactly 128 unique combinations of 7 bits, this 7-bit code can represent only128 characters. Another version is ASCII-8, also called extended ASCII, which uses 8 bits for each character, can represent 256 different characters.

For example, the letter A is represented by 01000001, B by 01000010 and so on. ASCII code is enough to represent all of the standard keyboard characters.

### EBCDIC

It stands for Extended Binary Coded Decimal Interchange Code. This is similar to ASCII and is an 8 bit code used in computers manufactured by International Business Machine (IBM). It is capable of encoding 256 characters.

If ASCII coded data is to be used in a computer that uses EBCDIC representation, it is necessary to transform ASCII code to EBCDIC code. Similarly, if EBCDIC coded data is to be used in an ASCII computer, EBCDIC code has to be transformed to ASCII.

### ISCH

ISCII stands for Indian Standard Code for Information Interchange or Indian Script Code for Information Interchange. It is an encoding scheme for representing various writing systems of India. ISCII uses 8-bits for data representation.

It was evolved by a standardization committee under the Department of Electronics during 1986-88 and adopted by the Bureau of Indian Standards (BIS). Nowadays ISCII has been replaced by Unicode.

### Unicode

Using 8-bit ASCII we can represent only 256 characters. This cannot represent all characters of written languages of the world and other symbols. Unicode is developed to resolve this problem. It aims to provide a standard character encoding scheme, which is universal and efficient.

It provides a unique number for every character, no matter what the language and platform be. Unicode originally used 16 bits which can represent up to 65,536 characters. It is maintained by a non-profit organization called the Unicode Consortium.

The Consortium first published version 1.0.0 in 1991 and continues to develop standards based on that original work. Nowadays Unicode uses more than 16 bits and hence it can represent more characters. Unicode can represent characters in almost all written languages of the world.

## Data Representation of Audio, Image and Video

In most cases, we may have to represent and process data other than numbers and characters. This may include audio data, images, and videos. We can see that like numbers and characters, the audio, image, and video data also carry information.

We will see different file formats for storing sound, image, and video.

Multimedia data such as audio, image, and video are stored in different types of files. The variety of file formats is due to the fact that there are quite a few approaches to compressing the data and a number of different ways of packaging the data.

For example, an image is most popularly stored in Joint Picture Experts Group (JPEG ) file format. An image file consists of two parts – header information and image data. Information such as the name of the file, size, modified data, file format, etc. is stored in the header part.

The intensity value of all pixels is stored in the data part of the file. The data can be stored uncompressed or compressed to reduce the file size. Normally, the image data is stored in compressed form. Let us understand what compression is.

Take a simple example of a pure black image of size 400X400 pixels. We can repeat the information black, black, …, black in all 16,0000 (400X400) pixels. This is the uncompressed form, while in the compressed form black is stored only once and information to repeat it 1,60,000 times is also stored.

Numerous such techniques are used to achieve compression. Depending on the application, images are stored in various file formats such as bitmap file format (BMP), Tagged Image File Format (TIFF), Graphics Interchange Format (GIF), Portable (Public) Network Graphic (PNG).

What we said about the header file information and compression is also applicable for audio and video files. Digital audio data can be stored in different file formats like WAV, MP3, MIDI, AIFF, etc. An audio file describes a format, sometimes referred to as the ‘container format’, for storing digital audio data.

For example, WAV file format typically contains uncompressed sound and MP3 files typically contain compressed audio data. The synthesized music data is stored in MIDI(Musical Instrument Digital Interface) files.

Similarly, video is also stored in different files such as AVI (Audio Video Interleave) – a file format designed to store both audio and video data in a standard package that allows synchronous audio with video playback, MP3, JPEG-2, WMV, etc.

## FAQs About Data Representation in Computer

### What is number system with example?

Let us discuss some of the number systems. Computer architecture supports the following number of systems:
1. Binary Number System
2. Octal Number System
3. Decimal Number System

All modern computer systems store numbers internally using the binary system. As well as numbers,computers need to be able to store and process other information such as text and graphics. Since the computer itself can, at a primitive level, only store numbers, systems had to be developed to represent text and other data numerically.

#### Numeric Data Representation

In the A/L syllabus we have to learn 4 number systems use by computers.

• Binary Number System
• Octal Number System
• Decimal Number System

#### Binary Number System

• Binary number system uses the digits 0 and 1.
• The position values go up by a factor of two as you move left(multiplied by two).
• The position values go down by a factor of two as you move right(divided by two).
• Base is 2.
• Minimum number is 0 and maximum number is 1.

#### Octal Number System

• Base is 8.
• Octal number system uses the digits 0,1,2,3,4,5,6,7.
• Minimum number is 0 and maximum number is 7.

#### Decimal Number System

• The most commonly used number system used in day to day life.
• Base is 10.
• Decimal number system uses the digits 0,1,2,3,,4,5,6,7,8,9.
• Minimum number is 0 and maximum number is 9.

• Base is 16.
• The symbols in the hexadecimal number system uses 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F  Where, A=10 , B=11, C=12, D=13, E=14, F=15
• Minimum number is 0 and maximum number is F.

### Conversion Between Number System

#### Binary to Decimal

101010

1             0              1              0            1            0

(1*32)  +  (0*16)  + (1*8)  +  (0*4)  +  (1*2)  +   (0*1)

32 +  0  +8  + 0 + 2 + 0

42

#### Octal to Decimal

322

3                  2                2

(3*64)   +  (2*8)    +    (2*1)

192  +  16 + 2

210

A10

A                 1            0

(10*256) +  (1*16)  +  (0*1)

2560  + 16 + 0

2576

#### Decimal to Binary #### Decimal to Octal 2980(decimal)=05644(octal)

Otherwise,

• First convert into binary and do follows,

156(decimal)=10011100(binary)

10 011 100

10     =(1*2)+(0*1)             =2

011    =(0*4)+(1*2)+(1*1) =3

100   =(1*4)+(0*2)+(0*1) =4

234(octal)

156(decimal)= 234(octal) Otherwise,

First convert into binary and do follows,

156(decimal)=10011100(binary)

1001 1100

1001  =(1*8) +(0*4)+(0*2)+(1*1) =9

1100 =(1*8) +(1*4)+(0*2)+(0*1) =12(C)

### Basic Arithmetic & Logic Operations

0 + 0 = 0

0 + 1 =  1

1 + 0 = 1

1 + 1 = 0 carry 1

10110 + 11000 = 101110

234 + 220 = 454

127 + 432 = 561

• If addition is equal to 8 answer is 0 and carry 1

A10 + 125 = B35

546 + D23 =1269

• f addition is equal to 16 answer is 0 and carry 1

#### Bitwise Logic Operation

A                 B                     ( A` )A  NOT            A AND B        A OR B          A XOR B

0                   0                          1                               0                       0                       0

0                    1                          1                               0                       1                        1

1                     0                         0                              0                        1                        1

1                     1                          0                               1                        1                       0

NOT Operation

10111 => 01000

AND Operation

1100 AND 1110

1100

OR Operation

1100 AND 1110

1110

XOR Operation

1100 XOR 1110

0010

### Signed Number Representation

Signed Number representation is use for encode negative numbers in binary.These are methods used to represent signed numbers.

• Sign and magnitude representation
• One’s complement representation
• Two’s complement representation

#### Sign and magnitude representation

• Least important method of representing negative numbers.
• MSD(Most Significant Digit) is reserved for indicate sign bit.
• Remaining bits of the number indicate absolute number.

Sign bit 0 represent positive numbers.

Sign bit 1 represent negative numbers.

+10 => 0 0001010                              -10=> 1 0001010

8 bit number can represent values from -127 (11111111)  to +127 (01111111)

This method has two values for zero.

00000000 => +0                               10000000 => -0

#### One’s Complement Representation

1. First write down number as 8 bit positive number.
2. Convert 0s into 1s and 1s into 0s. (NOT Operation)

-15 => (+15)= 00001111

11110000

8 bit number can represent values from -127 (1000000)  to +127 (01111111)

This method has two values for zero.

00000000 => +0                               10000000 => -0

(+4) + (-1)

(+4) 0000 0100

(+1) 0000 0001

(-1) 1111 1110(One’s complement)

(+4) + (-1)=> 0000 0100 + 1111 1110 =1 00000010 => 00000010 +1= 00000011

#### Two’s complement Representation

1. First write down number as 8 bit positive number.
2. Convert 0s into 1s and 1s into 0s. (NOT Operation)
3. Add 1 to the 2nd step.

-15 => (+15)= 00001111

11110000   + 00000001 = 11110001

When add to numbers together (One’s complement addition) carry bit is ignored.

### Q & A

1. Which of the following has the lowest value?

34(8)        67(10)        2D(16)        100011(2)      11011(2)

Convert all numbers into binary form.5th answer has 5 digits and all the other answers have more than 5 digits.(after the conversion into binary ) So lowest value is 5th answer(11011(2))

2.What is the even number?

111(2)      57(8)       A3(16)     C2(16)     11(10)

If last digit is(LSD) odd ,it is a odd number, Otherwise it is a even number.So answer is  4th. No need to apply conversions.

3.Which one of the following represent the MSD and LSD of 0.025630 respectively?

0 and 3          2 and 3                 6 and 2                 2 and 6                   6 and 0

MSD is a first digit in a number(without 0). LSD is last digit in a  number(without 0). So answer is 3rd.(6 and 2)

4.B12(16) + 5CA(16) =

10DC(16)        FDC (16)                   10DC(8)            1FDC(16)            0DC(16)

5.Hexadecimal equivalent to the octal number 57

1F(16)     2F(16)       57(16)           17(16)         27(16)

6. 1461(8) – 763(8) =

476(8)         425(8)        415(8)        375(8)       435(8)

7. What is the 2’s complement of -55 and 10?

00110111,00001010                     11001000,11110101                      11001000,00001010

11001001,00001010                    11001001,11110110

10 is a positive number. So it written as binary conversion. (00001010) -55 is a negative odd number. So sign bit is a 1 (because negative number). Last digit should be 1 (because it is a odd number) No need to calculate both numbers. So answer is 4th(11001001,00001010   ).

8. Convert the binary number 1010.11 to decimal

10.5           100.125              10.75             10.375              10.7

1              0             1             0             .              1                   1

(8*1)     (4*0)     (2*1)      (1*0)       .           (0.5*1)        (0.25*1)

8      +      2                     .           0.5    +    0.25

10.75

9. Equivalent hexadecimal value of 101011101(2)

AE1                    13D                 13E               12C               DA1

Answer is 2nd. (13D) 1  0101 1101  (1 3   D)

10. What will be the answer if 10110  XOR with 10010?

00010                11011                  01100             00011              00100

In the   XOR,

A                              B                                   A XOR    B

0                               0                                          0

0                                1                                           1

1                                 0                                          1

1                                  1                                          0