A microassembler is a

computer program A computer program is a sequence or set of instructions in a programming language for a computer to Execution (computing), execute. It is one component of software, which also includes software documentation, documentation and other intangibl ...

that helps prepare a microprogram, called ''firmware'', to control the low level operation of a computer in much the same way an assembler helps prepare higher level code for a processor. The difference is that the microprogram is usually only developed by the processor manufacturer and works intimately with the

computer hardware Computer hardware includes the physical parts of a computer, such as the central processing unit (CPU), random-access memory (RAM), motherboard, computer data storage, graphics card, sound card, and computer case. It includes external devices ...

. On a microprogrammed computer the microprogram implements the operations of the

instruction set In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, s ...

in which any normal program (including both application programs and

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

s) is written. The use of a microprogram allows the manufacturer to fix certain mistakes, including working around hardware design errors, without modifying the hardware. Another means of employing microassembler-generated microprograms is in allowing the same hardware to run different

s. After it is assembled, the microprogram is then loaded to a control store to become part of the logic of a CPU's

control unit The control unit (CU) is a component of a computer's central processing unit (CPU) that directs the operation of the processor. A CU typically uses a binary decoder to convert coded instructions into timing and control signals that direct the op ...

. Some microassemblers are more generalized and are not targeted at a single computer architecture. For example, through the use of macro-assembler-like capabilities,

Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until ...

used their ''MICRO2'' microassembler for a very wide range of computer architectures and implementations. If a given computer implementation supports a writeable control store, the microassembler is usually provided to customers as a means of writing customized microcode. In the process of

microcode In processor design, microcode serves as an intermediary layer situated between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. It consists of a set of hardware-level instructions ...

assembly it is helpful to verify the microprogram with emulation tools before distribution. Nowadays, microcoding has experienced a revival, since it is possible to correct and optimize the firmware of processing units already manufactured or sold, in order to adapt to specific

s or to fix hardware bugs. However, a commonly usable microassembler for today's CPUs is not available to manipulate the microcode. Knowledge of a processor's microcode is usually considered proprietary information so it is difficult to obtain information about how to modify it.

External links

* * * * {{CPU technologies Assemblers