Early Systems

Early on, the OS didn’t provide much other than library functions for allocating memory.

Multiprogramming and Time Sharing

Afterwards, OSes provided more functionality like time sharing, where multiple processes could share work, especially during slow jobs like I/O. Soon afterwards, time sharing systems were born, because the idea of interactivity became more important, as many users could be using the same machine.

This also gave birth to the idea of protection, where processes shouldn’t be able to read each others memory.

The Address Space

We need an abstraction to manage data, and so, the idea of an address space was born, which can be visualized like this:

Code Stack | v ^ | Heap

This allows every process to seem like it owns all of virtual memory, but in reality, when it makes a call to address 0, it is forwarded to the actual address allocated for its process.

Goals

Thus, we decide to virtualize memory. However, we do so with these goals:

1. Transparency: Processes shouldn’t need to know about virtual memory.
2. Efficiency: The OS should make this process cheap.
3. Protection: The OS should protect processes from one another.

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