Relocation and Protection (see the Fig. 4.5)

• when a program is linked, the linker must know at what address the program will begin in the memory
• In order to provide basic protection among programs sharing the memory, partitioning techniques use a hardware capability known as memory address mapping, or address translation
• suppose that the first instruction is a call to a procedure at absolute address 100 within the binary file produced by the linker
• if this program is loaded in partition 1 (at address 100 K, see the Fig. 4.4), that instruction will jump to to absolute address 100, which is inside the operating system
• what is needed is a call to 100K+100
• this problem is known as the relocation problem possible solution is is to modify the instructions as the program loaded into memory
• relocation during loading does not solve the protection problem
• A solution to both the relocation and protection problems is to equip the machine with two special hardware registers, called the base and limits registers

Figure 4.5: Address Translation.