Computer Codes notes for competitive exams — BCD, ASCII, EBCDIC, Unicode & ISCII explained with comparisons and quick revision tables.
What are Computer Codes?
Computer Codes are systems used to represent characters, letters, numbers, and symbols in binary form (0s and 1s) so that a computer can store, process, and communicate data. Since a computer only understands binary language, every character typed on a keyboard is converted into a unique code internally.
Coding systems became necessary because computers needed a standard way to represent alphabets, digits, punctuation marks, and special symbols in electronic form.
Why Computer Codes are Needed
| Reason | Explanation |
|---|---|
| Standardization | Ensures all computers interpret characters the same way |
| Data Exchange | Allows different systems/devices to share data correctly |
| Storage | Converts human-readable characters into machine-storable binary form |
| Multilingual Support | Enables representation of characters from different languages |
Major Computer Coding Systems
| Code | Full Form | Bits Used | Details |
|---|---|---|---|
| BCD | Binary Coded Decimal | 4 bits | Represents each decimal digit (0–9) using 4 binary bits |
| EBCDIC | Extended Binary Coded Decimal Interchange Code | 8 bits | Developed by IBM, supports 256 characters, used in mainframe computers |
| ASCII | American Standard Code for Information Interchange | 7 bits (standard), 8 bits (extended) | Most widely used code, supports 128/256 characters |
| Unicode | Universal Character Encoding Standard | 16 bits (UTF-16), variable (UTF-8) | Supports over 1,00,000 characters, covers almost all world languages |
| ISCII | Indian Script Code for Information Interchange | 8 bits | Developed in India to represent Indian language scripts (Devanagari, Tamil, etc.) |
BCD (Binary Coded Decimal)
BCD represents each digit of a decimal number individually using 4 binary bits.
Example:
Decimal 25 in BCD:
2 = 0010
5 = 0101
So, 25 in BCD = 0010 0101
Note: This is different from converting the full decimal number into binary directly.
ASCII (American Standard Code for Information Interchange)
ASCII is the most commonly used character encoding system in computers and communication equipment.
| Type | Bits | Characters Supported |
|---|---|---|
| Standard ASCII | 7 bits | 128 characters (0–127) |
| Extended ASCII | 8 bits | 256 characters (0–255) |
ASCII covers English alphabets (uppercase and lowercase), digits (0–9), punctuation marks, and control characters.
Example: The ASCII value of capital letter A is 65, and for lowercase a it is 97.
EBCDIC (Extended Binary Coded Decimal Interchange Code)
EBCDIC was developed by IBM and is mainly used in IBM mainframe and midrange computer systems. It uses 8 bits and can represent up to 256 different characters. It is not compatible with ASCII, meaning data conversion is required when exchanging data between EBCDIC-based and ASCII-based systems.
Unicode
Unicode was developed to overcome the limitation of ASCII, which could only represent English characters. Unicode provides a unique number for every character regardless of the platform, program, or language.
| Format | Description |
|---|---|
| UTF-8 | Variable-length encoding (1 to 4 bytes), most widely used on the web |
| UTF-16 | Fixed 16-bit encoding |
| UTF-32 | Fixed 32-bit encoding |
Unicode supports almost all writing systems in the world, including Hindi, Chinese, Arabic, and many more.
ISCII (Indian Script Code for Information Interchange)
ISCII is an 8-bit encoding scheme developed by the Government of India (Bureau of Indian Standards) for representing characters of Indian languages such as Hindi, Bengali, Tamil, Telugu, and others. It was later merged into the Unicode standard.
Difference Between ASCII, EBCDIC, and Unicode
| Feature | ASCII | EBCDIC | Unicode |
|---|---|---|---|
| Developed By | ANSI | IBM | Unicode Consortium |
| Bits Used | 7/8 bits | 8 bits | 16 bits/variable |
| Characters Supported | 128/256 | 256 | 1,00,000+ |
| Language Support | Mainly English | Mainly English | All world languages |
| Common Usage | PCs, Internet | Mainframes | Modern software, web, mobile |
Important Related Terms
| Term | Meaning |
|---|---|
| Character Set | Complete list of characters recognized by a coding system |
| Code Point | A unique number assigned to a character in Unicode |
| Parity Bit | An extra bit added to a code for error detection |
| Collating Sequence | Order in which characters are arranged (used for sorting) |
Quick Revision Table (Most Asked Facts)
| Fact | Answer |
|---|---|
| Full form of BCD | Binary Coded Decimal |
| Full form of ASCII | American Standard Code for Information Interchange |
| Full form of EBCDIC | Extended Binary Coded Decimal Interchange Code |
| Full form of ISCII | Indian Script Code for Information Interchange |
| Bits used in standard ASCII | 7 bits |
| Bits used in extended ASCII | 8 bits |
| Bits used in EBCDIC | 8 bits |
| Coding system developed by IBM | EBCDIC |
| Coding system supporting all world languages | Unicode |
| Coding system developed for Indian languages | ISCII |
| Bits used to represent one decimal digit in BCD | 4 bits |
| Most widely used encoding on the web | UTF-8 (Unicode) |
