I was studying operating system concepts from galvin’s sixth edition and i have some questions about the flow of execution of a program. A figure explains the processing of the user program as:
We get an executable binary file when we reach linkage editor point. As the book says, “The program must be brought into memory and placed within a process for it to be executed” Now some of my stupid questions are:
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Before the program is loaded into the memory, the binary executable file generated by the linkage editor is stored in the hard disk. The address where the binary executable file is stored in the hard disk is the logical address as generated by the CPU ?
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If the previous answer is yes, Why CPU has to generate the logical address ? I mean the executable file is stored somewhere in the hard disk which pertains to an address, why does CPU has to separately do the stuff ? CPU’s main aim is processing after all!
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Why does the executable file needs to be in the physical memory i.e ram and can not be executed in the hard disk? Is it due to speed issues ?
I know i am being stupid in asking these questions, but trust me, I can’t find the answers! 😐
1) The logical address where the binary file is stored in the hard disk is determined by the
file system, theOperating Systemcomponent that is aimed to manage files in the disks.2) & 3) The Hard Disk is not a) fast enough b) does not support word addressing. The hard disks are addressed in sectors blocks. Usually the sector size is 512 bytes. The CPU need to be able to address each machine word in a program to execute it. So, the program is stored in the hard disk, that retains its content even being powered off (in contrast to the RAM that losts its content when it is powered off). Then the program is loaded into RAM to be executed. After program finished and possibly stored the result of its execution in the hard disk, the memory is freed for running another programs. The Compiler and the Linkage Editor in your sample are also programs. They are kept in the hard disk. The compiler get its input (the source text of your program) from the file in the hard disk. Then it stores the object file. The linkage editor, or linker for short does the same: it reads the object file and necessary library files and then produces a file with a binary representation of your program.