# memory address register

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

**Wikidata**: [Q583538](https://www.wikidata.org/wiki/Q583538)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Memory_address_register)  
**Source**: https://4ort.xyz/entity/memory-address-register

## Summary
A memory address register (MAR) is a central processing unit (CPU) register that holds the specific memory address for the next data operation. It stores the location from which data will be fetched for the CPU or the address to which data will be sent and stored in memory. This register is a crucial component for the computer's read and write operations.

## Key Facts
- **Classification:** The memory address register is a subclass of processor register.
- **Primary Function:** It stores the memory address for fetching data from memory or for sending data to be stored in memory.
- **Parent Class:** As a processor register, it is a form of immediately accessible working storage available as part of a digital processor.
- **Aliases:** It is also known by the aliases MAR, registro de direcciones de memoria, RAM, and SAR.
- **Digital Presence:** The entity has a Wikipedia article in at least 10 languages, including English, Spanish, and German.
- **Sitelink Count:** The entity has a sitelink count of 12.
- **Unique Identifiers:** Its Freebase ID is /m/0519w and its discontinued Microsoft Academic ID was 47062644.

## FAQs
### Q: What is the main purpose of a memory address register?
A: The main purpose of a memory address register (MAR) is to hold the memory address of the data or instruction that needs to be accessed. It acts as the CPU's pointer, indicating exactly where in memory to read from or write to during a data transfer operation.

### Q: What does MAR stand for?
A: MAR stands for Memory Address Register.

### Q: Is a memory address register a type of processor register?
A: Yes, a memory address register is a specific type, or subclass, of a processor register. Processor registers are high-speed, immediately accessible storage locations located within the CPU.

## Why It Matters
The memory address register (MAR) is fundamental to the operation of a computer, acting as the critical link between the CPU and the main memory. Every time the processor needs to read an instruction or a piece of data from memory, or write a result back to memory, the MAR is involved. It solves the essential problem of locating specific data within the vast array of memory locations.

By holding the precise address for the current memory operation, the MAR ensures that the CPU interacts with the correct data. Without it, the processor would have no mechanism to specify which memory location to access, making the fetch-decode-execute cycle impossible. Its role is central to program execution, data manipulation, and the overall function of the von Neumann architecture that underpins most modern computers. The efficiency and speed of the interaction between the CPU and memory are directly dependent on the function of registers like the MAR.

## Notable For
- **Dedicated Function:** Unlike general-purpose registers that can hold various types of data, the MAR is specifically dedicated to one task: storing memory addresses for data transfer operations.
- **Dual-Role in Memory Access:** The MAR is integral to both read (fetch) and write (store) operations. It holds the target address whether the CPU is retrieving data from memory or sending data to be stored in memory.
- **Immediate Accessibility:** As a processor register, the MAR is a form of working storage that is immediately accessible to the processor. This high-speed access is crucial for efficient CPU performance.

## Body
### Function and Operation
The memory address register (MAR) is a crucial register within a computer's CPU. Its function is defined by its role in the two primary memory operations:

*   **Fetching Data:** When the CPU needs to read data or an instruction from memory, it places the address of that memory location into the MAR. The memory system then uses this address to find and return the requested data.
*   **Storing Data:** When the CPU needs to write data to memory, it places the destination address into the MAR. Simultaneously, the data to be written is placed in another register (like the Memory Data Register), and the memory controller stores the data at the address specified by the MAR.

### Classification and Identification
The memory address register is formally classified as a **processor register**. This category of components is defined as immediately accessible working storage that is part of a digital processor.

The entity is known by several aliases and identifiers:
*   **Common Acronym:** MAR
*   **Aliases:** registro de direcciones de memoria (Spanish), RAM, SAR
*   **Freebase ID:** /m/0519w
*   **Microsoft Academic ID:** 47062644 (discontinued)

### Digital Footprint
The concept of the memory address register is well-documented across digital knowledge bases. It has a dedicated Wikipedia page titled "Memory address register," which is available in at least 10 languages, including:
*   `ar` (Arabic)
*   `de` (German)
*   `en` (English)
*   `es` (Spanish)
*   `fr` (French)
*   `it` (Italian)
*   `ko` (Korean)

## References

1. Freebase Data Dumps. 2013