Microcode is the lowest specified level of processor and machine instructions sets. It is a layer comprised of small instruction sets, which are derived from machine language. Microcode performs short, control-level register operations, including multiple microinstructions, each of which performs one or more micro-operations.
Microcode and machine language differ. Machine language operates at the hardware abstraction’s upper layer.
Machine language interprets and sends machine instructions to the lowest hardware layer level where they are translated into small microprograms called microcodes.
Example of usage – “Microcode is stored in the ROM or in the erasable programmable ROM (EPROM) and cannot easily be modified by generic programmers. Microcode tasks include connecting different registers using arithmetic logic units, performing mathematical calculations, and saving the results in the register.”