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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 micro instructions, each of which performs one or more micro operations.
Microcode and machine language differ. Machine language operates at the hardware abstraction’s upper layer. However, microcode deals with lower-level or circuit-based operations. Because microcode is usually embedded in hardware, it cannot be altered.
Microcode is the result of lower-level machine language interpretation. It manages hardware resources at the register or circuitry level. Machine language interprets and sends machine instructions to the lowest hardware layer level where they are translated into small micro programs called microcodes. Each piece of microcode may contain one or more micro instructions, which perform circuit-based operations.
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.