Question

How does the logical vs. physical address space affect compilation, linking, and loading?

Answer 1

Solution:

Physical address space:

Physical Address refers to location in memory unit(the one that is loaded into memory). The set of all physical addresses corresponding to these logical addresses is referred to as a physical address space.

Logical address space:

Logical address is generated by CPU in perspective of a program. The set of all logical addresses generated by a program is referred to as a logical address space.

Virtual and physical addresses are the same in compile-time and load-time address-binding schemes. Virtual and physical addresses differ in execution-time address-binding scheme.

Now question arises, How does the logical vs. physical address space affect compilation, linking, and loading?

An address binding can be done in three different ways:

Compilation: If you know that during compile time where process will reside in memory then absolute address is generated i.e physical address is embedded to the executable of the program during compilation. Loading the executable as a process in memory is very fast. But if the generated address space is preoccupied by other process, then the program crashes and it becomes necessary to recompile the program to change the address space.

Loading: If it is not known at the compile time where process will reside then relocatable address will be generated. Loader translates the relocatable address to absolute address. The base address of the process in main memory is added to all logical addresses by the loader to generate absolute address. In this if the base address of the process changes then we need to reload the process again.

Linking: The instructions are in memory and are being processed by the CPU. Additional memory may be allocated and/or deallocated at this time. This is used if process can be moved from one memory to another during execution(dynamic linking-Linking that is done during load or run time). e.g – Compaction.

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