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Logical VS Physical Address Space In Operating System

Basically an address generated by the CPU is commonly referred  as a logical address, whereas an address seen by the memory unit is commonly referred as a physical address.The compile-time and load-time address-binding methods generate identical logical and physical addresses. However, the execution-time address binding scheme results in differing logical and physical addresses. In this case, we usually refer to the logical address as a virtual address.


The set of all logical addresses generated by a program is a logical address space. The set of all physical addresses corresponding to these logical addresses is a physical address space. Thus, in the execution-time address-binding scheme, the logical and physical address spaces differ. The run-time mapping from virtual to physical addresses is done by a hardware device called the memory-management unit (MMU).


The user program generates only logical addresses and thinks that the process runs in locations 0 to max. However, these logical addresses must be mapped to physical addresses before they are used. The concept of a logical address space that is bound to a separate physical address space is central to proper memory management.



Logical Address is generated by CPU while running of program. The logical address is virtual address. This address is used as a reference to access the physical memory location by CPU. The hardware device called Memory-Management Unit is used for mapping logical address to its corresponding physical address. Physical Address is a physical location of required data in a memory. The user never directly deals with the physical address. For access it uses its corresponding logical address. The user program generates the logical address and thinks that the program is running in this logical address but the program needs physical memory for its execution. So the logical address must be mapped to the physical address by MMU before they are used.


In other  words the physical address space in a system can be defined as the size of the main memory in a system. It is an important task to always compare the process size with the physical address space. The process size must be less than the available physical address space. Logical address space can be defined as the size of the process. The size of the process should be less enough so that it can reside in the main memory.


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