Logical Address vs. Physical Address in Operating System: What's the Difference?

Edited by Huma Saeed || By Sumera Saeed || Updated on October 12, 2023

A logical address is generated by a CPU during a program’s execution, whereas a physical address refers to a location in a computer’s memory hardware. Both facilitate data retrieval in computing.

Key Differences

A logical address, also known as a virtual address, emerges as a particular outcome of a CPU’s computational operations. Essentially, when a program initiates a data retrieval or storage operation, the logical address indicates where in the logical memory space this operation should occur. Contrarily, a physical address pertains explicitly to the physical memory locations within the computer's RAM. It designates an exact, tangible location in the memory hardware where data is stored, unmediated by additional abstraction layers.

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Operating systems utilize the logical address as a reference point in the abstraction of actual physical memory locations. It acts as an intermediary, with the Memory Management Unit (MMU) translating logical addresses to physical ones. Conversely, physical addresses interact directly with the memory hardware, devoid of such translational steps, as they directly point towards the physical memory locations, providing unadulterated access to the actual memory hardware.

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The logical address space represents a layer of abstraction provided by the operating system that enables simplified memory management and isolation between different running programs. The operating system and MMU collaborate to assure that logical addresses from various programs are transmuted into accurate, conflict-free physical addresses. In contrast, the physical address space doesn’t necessitate such comprehensive management due to its intrinsic correspondence with the tangible memory hardware.

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Logical addresses enable an operating system to execute functionalities like memory protection, virtual memory, and swapping effectively. This is possible by isolating the actual memory address from the processes, offering a degree of protection and control. Physical addresses are devoid of this intermediate layer, representing the actual, physical boundaries and locales within the RAM, and therefore, do not directly facilitate such functionalities.

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When a program interacts with memory, it generates logical addresses, as these addresses provide a standardized, simplified interface for memory interaction and isolation from other processes. In contrast, physical addresses function as the ultimate recipients of these interactions after translation, being the loci in the memory hardware where the read or write actions are actually enacted, thereby serving as the practical memory interface for the hardware.

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Comparison Chart

Nature

Abstract and generated by CPU.

Concrete and corresponds to hardware location.

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Utilization in Memory Access

Used by CPU when a program accesses memory.

Used by RAM to perform actual data storage/retrieval.

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Involvement in MMU Translation

Translated by MMU to obtain a physical address.

Directly accessed without MMU translation.

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Interaction with OS Functions

Facilitates OS features like memory protection.

Does not inherently facilitate such functionalities.

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Dependency

Independent of current physical memory state.

Directly dependent on actual memory hardware.

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Logical Address and Physical Address in Operating System Definitions

Logical Address

Logical addresses are utilized within the context of virtual memory and memory management systems.

In virtual memory systems, logical addresses undergo translation via the MMU to correspond with physical memory locations.

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Physical Address in Operating System

Physical addresses are derived from logical addresses through the translation process of the Memory Management Unit (MMU).

The MMU efficiently translates a logical address into a physical address to communicate with the actual memory hardware.

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Logical Address

A logical address is a virtual memory address generated by the CPU during program execution.

During its runtime, a program utilizes logical addresses to reference memory locations, abstracting the physical address intricacies.

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Physical Address in Operating System

Physical addresses remain static and correlate to fixed locations in the computer’s hardware.

Each byte of the computer’s RAM is uniquely identifiable via a singular physical address.

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Logical Address

Logical address space is a contiguous addressable memory range presented to a program.

A logical address acts as an intermediary, helping programs interact with memory without direct hardware addressing.

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Physical Address in Operating System

Physical addresses ensure direct, immediate access to a memory location, bypassing the abstract layer provided to the software by logical addresses.

When data is retrieved, the system accesses it directly from its physical address in the memory hardware.

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Logical Address

Logical addresses allow the operating system to implement features like memory isolation and protection.

By interacting through logical addresses, programs can securely access memory, protected from direct hardware interventions.

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Physical Address in Operating System

A physical address correlates directly to a location within a computer’s physical memory hardware.

When data is stored, it occupies a specific physical address in the RAM.

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Logical Address

Logical addresses facilitate the decoupling of a program’s memory access from the actual physical memory locations.

Logical addresses allow programs to operate without requiring knowledge of actual memory hardware locations.

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Physical Address in Operating System

Physical addresses in an OS directly interact with the computer’s memory hardware without abstraction layers.

Physical addresses pinpoint the exact location where data is stored within the computer’s RAM.

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FAQs

How does a physical address function?

Physical addresses provide the exact location of data in memory hardware, ensuring direct access to data storage points.

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How is a logical address used in an OS?

Logical addresses allow software to access memory through a layer of abstraction, facilitating memory management and protection.

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What is a logical address?

A logical address is a CPU-generated address that enables a program to access physical memory indirectly through abstraction.

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Can a physical address refer to different types of physical memory?

Yes, a physical address may point to various memory types like RAM, cache, or other hardware storage.

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Why is a logical address needed?

Logical addresses provide a method to access physical memory indirectly, enabling enhanced memory management and protection.

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Is a physical address visible to a running program?

Typically, no. Programs interact with logical addresses, which are then translated to physical addresses by the MMU.

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Can two logical addresses point to the same physical address?

Generally, no. Unique logical addresses are mapped to unique physical addresses to prevent data conflicts.

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What is logical address space?

It is the set of all logical addresses generated by a program during its execution.

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Is the logical address the same as a virtual address?

Yes, logical addresses are often referred to as virtual addresses.

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How do logical addresses aid in memory protection?

They prevent direct program access to physical memory, thereby safeguarding memory segments from unauthorized or accidental access.

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Does swapping affect logical or physical addresses?

Swapping involves moving data between RAM and disk storage but logically addressed data retains its address while physical address may change.

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How is memory access time managed with logical and physical addresses?

Logical addresses manage memory through abstraction to optimize access, while physical addresses interact directly, providing the real access time to the hardware memory.

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Can a physical address change during execution?

No, physical addresses correspond to fixed locations in memory hardware.

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What is the significance of physical addresses in memory read/write operations?

Physical addresses pinpoint exact locations in memory hardware where read/write operations are physically executed.

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Can physical and logical addresses be the same?

In some systems (e.g., without virtual memory), logical and physical addresses may be the same.

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Is it possible to access a physical address directly in high-level programming?

Typically, no. High-level programming languages interact with logical addresses, maintaining a layer of abstraction from physical addresses.

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Are logical addresses related to address binding?

Yes, address binding determines the mapping from logical to physical addresses.

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What is a physical address?

A physical address is a location in the computer's memory hardware and interacts directly with RAM.

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What facilitates logical to physical address translation?

The Memory Management Unit (MMU) facilitates this translation.

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How does the MMU work regarding logical addresses?

The MMU translates logical addresses generated by a CPU into corresponding physical addresses in RAM.

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About Author

Written by

Sumera is an experienced content writer and editor with a niche in comparative analysis. At Diffeence Wiki, she crafts clear and unbiased comparisons to guide readers in making informed decisions. With a dedication to thorough research and quality, Sumera's work stands out in the digital realm. Off the clock, she enjoys reading and exploring diverse cultures.

Edited by

Huma is a renowned researcher acclaimed for her innovative work in Difference Wiki. Her dedication has led to key breakthroughs, establishing her prominence in academia. Her contributions continually inspire and guide her field.