Summary ch8

1. Memory Management: Memory needs to be allocated to ensure a reasonable supply of ready processes to consume available processor time

2. Memory Management Requirements:

   -Protection: Processes should not be able to reference memory locations in another process without permission

   -sharing: Allow several processes to access the same portion of memory

   -Relocation: While the program is executing, it may be swapped to disk and returned to main memory at a different location (relocated); Memory references in the code must be translated to actual physical memory address

3. Steps for loading a process in memory:

   

4. Address Binding

   -Source program: symbolic (such as count)

   -After compiling: re-locatable address

   -After linkage editor, loader or run-time referring: absolute address

   

5. Binding at Compile Time

6. Binding at load time Must generate re-locatable code if memory location is not known at compile time -Physical memory address is fixed at load time -Must reload if starting location changes

7. Binding in execution time

   Binding delayed until run time

8. Logical vs. Physical Address Space

   The concept of binding a logical address space to a physical address space is central to proper memory management

   -Logical address – generated by the CPU; also referred to as virtual address

   -Physical address– address seen by the memory unit

   In compile-time and load-time address-binding schemes, logical and physical addresses are the same

   In execution-time address-binding scheme, logical and physical addresses differ

9. Memory Management Techniques

   -Fixed Partitioning

   -Dynamic Partitioning

   -Simple Paging

   -Simple Segmentation

   -Virtual Memory Paging

   -Virtual Memory Segmentation

10. Fixed Partitioning

    -Equal-size partitions

11. Dynamic Partitioning

    -Partitions are of variable length and number

    -Process is allocated exactly as much memory as required, no internal fragmentation

    Problem: Eventually get holes in the memory. This is called external fragmentation

    -Must use compaction to shift processes so they are contiguous and all free memory is in one block

12. Contiguous vs. Non-contiguous Memory Allocation

    -The memory management techniques discussed so far all require the physical address space of a process to be contiguous

    -Paging and Segmentation permit the physical address space of a process to be non-contiguous

13. Paging

    -Partition memory into small equal fixed-size chunks and divide each process into the same size chunks

    -The chunks of a process are called pages

    -The chunks of memory are called frames