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When an operating system or executive uses paging, the paging mechanism is transparent to an application program. All that the application sees is a linear address space.

The address space used by a process is a virtual (memory) address space.

When the memory was still not virtual, in the first computers, the amount of available RAM had to be greater than the address space of the largest application to be run; otherwise, the application would fail with an “out of memory” error.

The address space of a process is the number of unique addresses needed to hold both:

  • the code (the application)
  • and its data

Threads share the same address space than the process that created them.

See also: Process - Memory

Example

Application Memory Needs Size (bytes)
Application Code 10000
Data storage and I/O buffers 5000
Total to be able to run 15000

This 15000 byte requirement is known as the application address space