In a

computer A computer is a machine that can be programmed to Execution (computing), carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as C ...

, the memory address register (MAR) is the

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

register that either stores the memory address from which data will be fetched to the CPU registers, or the address to which data will be sent and stored via

system bus A system bus is a single computer bus that connects the major components of a computer system, combining the functions of a data bus to carry information, an address bus to determine where it should be sent or read from, and a control bus to dete ...

. In other words, this register is used to access data and instructions from memory during the execution phase of instruction. MAR holds the memory location of data that needs to be accessed. When reading from memory, data addressed by MAR is fed into the

MDR MDR may refer to: Biology * MDR1, an ATP-dependent cellular efflux pump affording multiple drug resistance * Mammalian Diving reflex * Medical device reporting * Multiple drug resistance, when a microorganism has become resistant to multiple drugs ...

(memory data register) and then used by the CPU. When writing to memory, the CPU writes data from MDR to the memory location whose address is stored in MAR. MAR, which is found inside the CPU, goes either to the RAM ( random-access memory) or cache. The MAR register is half of a minimal interface between a

microprogram In processor design, microcode (μcode) is a technique that interposes a layer of computer organization between the central processing unit (CPU) hardware and the programmer-visible instruction set architecture of a computer. Microcode is a lay ...

and

computer storage Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processing unit (CPU) of a compute ...

; the other half is a

. In general, MAR is a parallel load register that contains the next memory address to be manipulated, for example the next address to be read or written.

References

Digital registers {{Compu-hardware-stub