microprogramming, process of writing microcode for a microprocessor. Microcode is low-level code that defines how a microprocessor should function when it executes machine-language instructions. Typically, one machine-language instruction translates into several microcode instructions. On some computers, the microcode is stored in ROM (read-only memory) and cannot be modified; on some larger computers, it is stored in EPROM (erasable programmable read-only memory) and therefore can be replaced with newer versions.