Data Representation notes for competitive exams — number systems, bit/byte units, ASCII, Unicode & conversions with quick revision tables.
What is Data Representation?
Data Representation refers to the method/form in which data is stored, processed, and transmitted inside a computer. Computers understand only binary form (0s and 1s), so all data (numbers, text, images, audio, video) must be converted into binary before processing.
Computers are digital devices — they work on the principle of electronic signals being ON (1) or OFF (0).
Number Systems (Very Important)
A Number System defines a set of values used to represent quantities.
| Number System | Base | Digits Used |
|---|---|---|
| Binary | 2 | 0, 1 |
| Octal | 8 | 0–7 |
| Decimal | 10 | 0–9 |
| Hexadecimal | 16 | 0–9, A–F |
Decimal is the number system humans use daily. Binary is the number system computers use internally.
Binary Number System (Base 2)
Binary uses only two digits: 0 and 1. Every piece of data in a computer is ultimately stored as a combination of these two digits.
Example:
- Decimal 10 = Binary 1010
- Decimal 5 = Binary 101
Basic Data Units (Extremely Important — Direct Questions)
| Unit | Meaning |
|---|---|
| Bit | Binary Digit — smallest unit of data (0 or 1) |
| Nibble | Group of 4 bits |
| Byte | Group of 8 bits — represents one character |
| Kilobyte (KB) | 1024 Bytes |
| Megabyte (MB) | 1024 KB |
| Gigabyte (GB) | 1024 MB |
| Terabyte (TB) | 1024 GB |
| Petabyte (PB) | 1024 TB |
| Exabyte (EB) | 1024 PB |
Memory Order (Ascending): Bit → Nibble → Byte → KB → MB → GB → TB → PB → EB → Zettabyte → Yottabyte
Character Encoding Systems (Important)
These are systems used to represent characters (letters, numbers, symbols) using binary codes.
| Encoding | Full Form | Bits Used | Characters Supported |
|---|---|---|---|
| ASCII | American Standard Code for Information Interchange | 7 bits (originally), 8 bits (extended) | 128 (standard), 256 (extended) |
| EBCDIC | Extended Binary Coded Decimal Interchange Code | 8 bits | 256 |
| Unicode | Universal Character Encoding | 16 bits (UTF-16) / variable (UTF-8) | Over 1,00,000+ characters (supports all world languages) |
ASCII is mainly used in personal computers, while Unicode was developed to support multiple languages worldwide (since ASCII could not represent non-English characters).
Types of Data
| Type | Description | Example |
|---|---|---|
| Numeric Data | Numbers used for calculations | 123, 45.6 |
| Text/Alphanumeric Data | Letters, numbers, symbols | “Hello123” |
| Image Data | Pictures/graphics represented as pixels | JPG, PNG |
| Audio Data | Sound represented digitally | MP3, WAV |
| Video Data | Moving images with sound | MP4, AVI |
Analog vs Digital Data
| Aspect | Analog | Digital |
|---|---|---|
| Signal Type | Continuous signal | Discrete signal (0s and 1s) |
| Example Device | Old telephone, thermometer | Computer, digital watch |
| Accuracy | Less accurate (prone to noise) | More accurate |
Number System Conversions (Concept Only)
| Conversion | Method |
|---|---|
| Decimal to Binary | Repeated division by 2, note remainders |
| Binary to Decimal | Multiply each bit by 2 raised to its position value, then sum |
| Decimal to Octal | Repeated division by 8 |
| Decimal to Hexadecimal | Repeated division by 16 |
Example (Decimal to Binary):
10 ÷ 2 = 5 remainder 0
5 ÷ 2 = 2 remainder 1
2 ÷ 2 = 1 remainder 0
1 ÷ 2 = 0 remainder 1
Reading remainders bottom to top: 1010
So, Decimal 10 = Binary 1010
Important Related Terms
| Term | Meaning |
|---|---|
| Pixel | Smallest unit of a digital image (Picture Element) |
| Resolution | Number of pixels in an image (higher = clearer image) |
| Word | Group of bits a CPU processes at one time (e.g., 32-bit, 64-bit) |
| BCD | Binary Coded Decimal — represents each decimal digit using 4 binary bits |
Quick Revision Table (Most Asked Facts)
| Fact | Answer |
|---|---|
| Smallest unit of data | Bit |
| 8 bits equal to | 1 Byte |
| 1024 Bytes equal to | 1 Kilobyte |
| 1024 KB equal to | 1 Megabyte |
| Number system with base 2 | Binary |
| Number system with base 16 | Hexadecimal |
| Character encoding using 7/8 bits | ASCII |
| Character encoding supporting all world languages | Unicode |
| Full form of ASCII | American Standard Code for Information Interchange |
| Full form of EBCDIC | Extended Binary Coded Decimal Interchange Code |
| Smallest unit of a digital image | Pixel |
| 4 bits equal to | 1 Nibble |
