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Lecture 15

Chapter 8: Main Memory

Chapter 8: Memory Management

• Background

• Swapping

• Contiguous Memory Allocation

• Paging

• Structure of the Page Table

• Segmentation

• Example: The Intel Pentium

Background

• Program must be brought (from disk) into memory

and placed within a process for it to be run

• Main memory and registers are only storage CPU

can access directly

• Register access in one CPU clock (or less)
• Main memory can take many cycles
• Cache sits between main memory and CPU registers
• Protection of memory required to ensure correct

operation

Base and Limit Registers

• A pair of base and limit registers define

the logical address space

Multistep Processing of a User Program

Logical vs. Physical Address Space

• The concept of a logical address space that is bound to a separate 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
• They are the same in compile-time and load-time address-binding schemes;
• They differ in execution-time address-binding scheme