Processes are executed functions.
The OS:

Multitasking

OS allocates time to every process. Processes get switched back and forth.

Virtual Memory Space

Each process gets a virtual memory space, which isolated form other processes virtual memory.

Virtual addresses

Physical Memory Space

0x00000000 to 0x3FFFFFFF ae reserved for special devices.
If we have 2 GiB of RAM, the end address of our physical memory space is 0xBFFFFFFF.

Memory Pages