The [[6502]] processor has 13 [[Addressing Mode|Addressing Modes]], which affect how the arguments for instructions are accessed.  For example, the Load Accumulator <code>LDA</code> instruction can load the accumulator from different sources:  LDA #$05 ; Immediate addressing mode - load the accumulator with the number 5 LDA $05 ; Zero-page addressing mode - load the accumulator from memory address 5 LDA $0805 ; Absolute addressing mode - load the accumulator from memory address 0x8005 (32773). Not all addressing modes are valid for every instruction.