Encoding of Information

• In computers, encoding is the process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized format for efficient transmission or storage.
• Decoding is the opposite process -- the conversion of an encoded format back into the original sequence of characters.
• Encoding and decoding are used in data communications, networking, and storage.
• The code used by most computers for text files is known as ASCII (American Standard Code for Information Interchange).
• ASCII can depict uppercase and lowercase alphabetic characters, numerals, punctuation marks, and common symbols.
• Other commonly-used codes include Unicode, BinHex and Uuencode.
• In data communications, Manchester encoding is a special form of encoding in which the binary digits (bits) represent the transitions between high and low logic states.

Operation Code (Opcode)

• It specifies the operation to be performed.
• The operation of the CPU is determined by the instructions it executes.
• The instructions are referred to as machine instructions or computer instructions.
• Each instruction must contain the information required by the CPU for execution.

Encoding and decoding

• It is important that the opcode word be easy to decode.
• A decoder that must examine a large number of opcode bits simultaneously requires a correspondingly large number of levels of logic gates and introduces a large delay.
• If the opcode is divided into small fields and a separate decoder is used for each field, the decoding delay will be much smaller.
• Three formats are used for data manipulation instructions and the fourth is used in flow control instructions such as branch and branch-to-subroutine.
• The opcode field also determines certain units which will be responsible for completing the execution of the instruction and so should read the information on the source buses.