In a
computer, 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
In computing, a memory address is a reference to a specific memory location used at various levels by software and hardware. Memory addresses are fixed-length sequences of digits conventionally displayed and manipulated as unsigned integers. ...
from which data will be fetched to the CPU registers, or the address to which data will be sent and stored via
system bus.
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
Random-access memory (RAM; ) is a form of computer memory that can be read and changed in any order, typically used to store working data and machine code. A random-access memory device allows data items to be read or written in almost t ...
) 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 laye ...
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 comput ...
; the other half is a
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 ...
.
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
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