Lecture 25: Introduction to Memory Management

Lecture 25: Introduction to Memory Management

Lecture 25: Introduction to Memory Management Overview of this course OS is a resource manager Process/threads Deadlocks Memory

Disk, i.e., file system Memory Management Ideal World (for the programmer): Im the only process in the world I have a huge amount of memory at my disposal

Real World Many processes in the system Probably not enough memory for them all Goal of Memory Management Present the ideal world view to the programmer, yet implement it on a real system

Virtual address vs. physical address Your program is compiled and linked Virtual address (also called absolute address) Virtual address vs. physical address Physical address Address to access memory of the machine

More detailed goals of memory management Memory allocation A new process comes into memory Memory de-allocation A process leaves memory

Address translation Virtual address to physical address Process isolation One process cannot access the memory of other processes

Memory management for different systems Processes are known in advance and can fit in memory Embedded systems, e.g., radios, washing machines, and microwaves Processes are unknown in advance, memory

might not be large enough Swapping Virtual memory Processes are known in advance Memory allocation Allocate a specific area to each process

Memory de-allocation Do not really need to do anything Why we need address translation (a) A 16 KB program, (b) another 16KB program (c) They are loaded consecutively in memory

Address translation Static address translation Map virtual address to physical address when loading a process into memory Used when processes are known in advance Dynamic address translation Map virtual address to physical address at

runtime Process isolation Divide the memory into blocks Each block has a protection key A process cannot access the memory whose protection key does not match

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