Opcode: Difference between revisions

Revision as of 04:18, 6 November 2004

Revision as of 05:27, 10 November 2004

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A computer can perform operations, each of which is assigned a numeric code called an '''opcode'''. To assist in the use of these numeric codes, [[mnemonic]]s are used as textual abbreviations. It's much easier to remember ADD than 05, for example.

Opcodes operate on [[processor register|registers]]s, values in [[memory]], values stored on the [[Stack (computing)|stack]], [[I/O]] ports, the [[Computer bus|bus]], etc. They are used to perform arithmetic operations and move and change values. Operands are the things that opcodes operate on.

[[Byte code]]s are another term for opcodes, especially when they are used to describe higher level constructs as is the case with the [[Java programming language|Java Language]]'s JVM ([[Java Virtual Machine]]). For instance, byte code 1A might be the "iconst_2" instruction which pushes the number 2 on the stack. This is a slightly higher level of abstraction than opcodes, which might need to load the number 2 into a register, and then push the register's value on the stack.