DIFFERENT TYPES OF CODES
Operation Code (opcode) : This field contains a binary code to specify various operations which must be performed by the CPU. For example, Add, Subtract, Shift, I/0 etc.
Source Operand Reference : This field specifies operands or operand that are inputs for the operation. In this field the operand location may be explicitly specified, as a memory address or general register number, or it may be implicit within the opcode or as a single accumulator etc.
Result Operand : After the operation is performed the result may need to be stored. This result location may be specified explicitly or it may be specified implicitly in the opcode.
Next Instruction Reference: This tells the CPU where to fetch the next instruction after the execution of this instruction is complete. This instruction is located in main memory. In a virtual memory system, it is located in either main memory or secondary memory. In this case this location address must be specified explicitly.
In most cases, the next instruction to be fetched immediately follows the current instruction and it does not need any explicit reference.