As a complex instruction set computer (CISC), the 8086 supports a rich array of operations, including multiple addressing modes such as register, immediate, and memory addressing.
The 8086's instruction set was designed with a new concept, the "ModR/M" byte, which usually follows the opcode byte. The ModR/M byte specifies the memory addressing mode and the register (or registers) to use, allowing that information to be moved out of the opcode.
Although most operations execute on 16‑bit operands, the chip allows manipulation of 8‑bit data as well—an important feature for compatibility with legacy 8‑bit software.