Logical Address - An Easier Discussion

An Easier Discussion

Before discuss both types of address lets set some premises. Physical address :- the original address of each bytes of any memory device. Its generally a binary number but for ease of use its usually represented in hex number. Logical address :- A logical address is the address generated by CPU,which is easier to handle and programs assume that they resides at this address,but these logical address only can indicate any memory location they are not directly associated with it.

let us consider we are using a 16 bit processor, Then my CPU is able to generate an 16 bit address ranging 0 to 216-1.but if we want to use a memory of capacity of 220 or 232 bytes, then we have to design an arithmetic expression which will translate a 16 bit value to a 20 or a 32 bit value. For example, my CPU will generate 4870h and the arithmetic operation will generate A9822h or CD234501h from the address generated by CPU .the arithmetic will increment or change exactly the same for each and every address . now the regenerated address can clearly represent a particular byte of the memory, and the initial address can indicate for it.

Finally Logical address : Logical address is the address generated by CPU that is not directly associated with any memory location, but the memory mapping function and the a memory management unit (MMU) between the CPU and the memory bus, translates it in to physical address.

Finally Physical address : The address directly associate with memory locations is physical address .for a large capacity of memory space the addressing gets growth proportional to size . thus processor use to generate a logical address of fewer bit size and lets MMU to interpret it into the original physical address.

Logical address or virtual address is also used in IBM's VM operating system and in Virtual Device Location.