Changes

===Instruction Set===

===Instruction Set===

The instruction set of a given CPU model defines the basic operations that can be performed by the CPU.  These operations tend to be simple, such as adding two numbers, outputting a character, or moving data between registers.  In a given line of processors, the instruction sets are compatible, although as the newer models are released, they usually had additional instructions added.  Thus, newer processors were backwards compatible (meaning they could run the same programs as older processors), but older processors did not recognize the new instructions added to later models.  Between processor lines, there is no compatibility.  The instructions are stored in memory as "machine code" which are bit patterns that represent certain instructions.  These bit patterns represent entirely different operations on different processor lines, which means that a program written for one CPU will not run on a different CPU line.  Rather than programming in machine code, assemblers are used to convert from mnemonics to machine codes.  The mnemonics tend to be three or four character abbreviations that indicate the operation.  For instance, MVI (Move immediate), JP (Jump if positive), or HLT (halt).

The instruction set of a given CPU model defines the basic operations that can be performed by the CPU.  These operations tend to be simple, such as adding two numbers, outputting a character, or moving data between registers.  In a given line of processors, the instruction sets are compatible, although as the newer models are released, they usually had additional instructions added.  Thus, newer processors were backwards compatible (meaning they could run the same programs as older processors), but older processors did not recognize the new instructions added to later models.  Between processor lines, there is no compatibility.  The instructions are stored in memory as "machine code" which are bit patterns that represent certain instructions.  These bit patterns represent entirely different operations on different processor lines, which means that a program written for one CPU will not run on a different CPU line.

There are two aspects to an instruction set.

There are two aspects to an instruction set.