Memory management requirements:
1. Relocation
2. Protection
3. Sharing
4. Logical Organization
5. Physical Organization
1. Relocation:
Programmer does not know where the program will be placed in memory when it is executed
while the program is executing, it may be swapped to disk and returned to main memory at a
different location (relocated). Memory references must be translated in the code to actual physical
memory address.
The address generated by CPU is said to be logical address. An address generated by MMU is
called physical address.
Physical address= Contents of Relocation register + logical address
2. Protection:
Processes should not be able to reference memory locations in another process without permission.
It must be checked at run time. Memory protection requirement must be satisfied by the processor
(hardware) rather than the operating system (software).
The word protection means provide security from
unauthorized usage of memory. The operating can protect the memory with the help of base and
limit register. Base registers consisting the starting address of next process. The limit specifies the
boundary of that job, so the limit register is also said to be fencing register.
3. Sharing:
Allow several processes to access the same portion of memory. It is better to allow each process
access to the same copy of the program rather than have their own separate copy.
