EBCDIC

Extended Binary Coded Decimal Interchange Code

What is EBCDIC?
Definition
Full form: Extended Binary Coded Decimal Interchange Code
Type: 8-bit character encoding (0–255 possible values)
Origin: Introduced by IBM in 1964 for the System/360 mainframe computers
Purpose: To represent letters, numbers, punctuation, and control characters in binary form
Why was it created?
Its predecessor BCDIC (Binary-Coded Decimal Interchange Code) was 6-bit and limited (only 64 symbols). IBM extended it to 8 bits → allowing 256 different symbols (suitable for international characters, symbols, and control codes).
How EBCDIC Works
Binary Representation
Every character (A–Z, 0–9, symbols, etc.) is assigned a unique 8-bit binary code. Text is stored/transmitted as a sequence of 8-bit values.
Lookup Table
A lookup table (mapping table) tells the computer which binary pattern corresponds to which character.
Character EBCDIC Code (binary) Decimal
'A' 1100 0001 193
'W' 1110 0111 231
'0' 1111 0000 240
Example: "WORLD" in EBCDIC
W → 11100111
O → 11001111
R → 11010010
L → 11000100
D → 11000011
The CPU stores/transmits these binary numbers, not the letters.
Real-World Examples
Banking Systems
Many bank mainframes still store customer records in EBCDIC format.
Airline Reservation
Global distribution systems (like Sabre, Amadeus) were originally EBCDIC-based.
Insurance & Government
Decades-old COBOL applications still rely on EBCDIC.
Data Exchange
Old tape archives and punched cards use EBCDIC encoding.
Compatibility Challenge
If two banks share customer files, and one uses ASCII while the other uses EBCDIC, they need translation middleware (EBCDIC ⇔ ASCII) to avoid misinterpreting characters.
Connection with Computer Organization & Architecture (COA)
Instruction Set Architecture (ISA)
IBM System/360 ISA included instructions that operated directly on EBCDIC codes, like compare, move, and translate instructions.

Example: TR (Translate) instruction could convert characters from one code page to another.
Memory Organization
Since EBCDIC is 8-bit fixed width, IBM mainframes standardized on byte = 8 bits.

This influenced memory word size and addressing in COA.
I/O Systems
IBM card readers, printers, and tape drives used EBCDIC as their default encoding.

Hardware controllers had to recognize and convert EBCDIC automatically.
Compatibility
Once IBM mainframes dominated the market, other vendors had to build hardware/software compatibility layers to handle EBCDIC data.

This shaped architecture choices in data exchange and system interconnect.
Advantages vs. Disadvantages
Advantages
  • Perfect for legacy support → thousands of COBOL mainframe applications still rely on it
  • Reliable & stable → same encoding scheme has worked for 50+ years
  • Supported internationalization earlier than ASCII (7-bit)
Disadvantages
  • Not widely used outside IBM mainframes → poor compatibility with modern PCs
  • Translation overhead needed (EBCDIC ⇔ ASCII)
  • Fewer people today know how to work with EBCDIC → talent shortage
  • Migration to modern systems is complex and risky
Conclusion
Key Takeaways
EBCDIC = IBM's legacy 8-bit encoding, designed for mainframes in the 1960s. Still alive in banking, insurance, airlines, and government because of massive legacy systems.
Influenced ISA design
Shaped memory architecture (byte = 8 bits)
Required I/O devices to be encoding-aware
Real-world example of encoding choices influencing hardware for decades
In Simple Words
EBCDIC is not just history — it's a real-world example of how encoding choices influence hardware, architecture, and software for decades.