A memory address space is the range of addresses a process or other execution context can use to refer to memory. On modern systems, a process’s virtual address space is a logical view: hardware and the operating system translate its virtual addresses to physical memory, so the range does not describe a chunk of RAM reserved just for that process.
What does “memory address space” mean?
The term describes the addresses available to a defined execution context. In the common operating-system context, it usually means a process’s virtual address space—the set of virtual memory addresses that process can use. Microsoft Learn defines it in those terms.
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A program uses addresses from its own view of memory. Those addresses identify locations in that view, not necessarily fixed locations in physical RAM. The operating system and processor’s memory-management hardware translate them according to the system’s mappings.
How virtual addresses map to physical memory
Memory is managed in pages. Page tables describe how virtual pages map to physical frames, and the processor consults these mappings when a program accesses memory. The page size depends on the host and architecture; for example, Microsoft gives 4 KB as an x86 page-size example, not a universal size. Microsoft Learn explains virtual address translation, and its discussion of physical storage and address space covers pages and residency.
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Two processes can use the same numeric virtual address while that address maps to different physical pages in each process. This separation helps isolate processes. Systems can also create mappings that are intentionally shared, so “private address space” does not mean sharing is impossible. The mapping, access controls, and memory-management rules determine what a process can actually access. See Microsoft’s overview of Windows virtual address spaces.
Address space is not RAM or working set
An address space is the range of addresses a context can use; it is not the amount of installed RAM and does not mean every address has a physical page resident at once. In Windows terminology, the working set is the subset of a process’s virtual pages currently resident in physical memory. Pages and their backing can be managed as system conditions change, so addressability and current physical residency are distinct properties. Microsoft documents this distinction between virtual address space, working set, and physical storage.
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| Term | What it describes |
|---|---|
| Virtual address space | The range of virtual addresses available to a process or other defined context. |
| Physical address | A hardware-facing location in physical memory after address translation. |
| Working set (Windows terminology) | The subset of a process’s virtual pages currently resident in physical memory. |
How large is an address space?
There is no single size that applies to every computer or process. Address-space limits depend on architecture, operating system, process type, and configuration. A processor’s theoretical address width is not, by itself, a promise that a process or operating system can use every possible address.
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For context, Microsoft documents a 4 GB total virtual address range for 32-bit Windows, divided by default between process and system use; the partition can vary with configuration, including 4GT. Its Windows driver documentation gives a 128 TB user-mode virtual address range for a 64-bit process on 64-bit Windows, while noting that only a portion of the theoretical 64-bit range is used. These are Windows-specific documented examples, not universal address-space definitions. See Microsoft’s Windows memory-management page and its driver documentation for their respective contexts.
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Address spaces in Linux
Linux describes a process address space as a collection of Virtual Memory Areas (VMAs). Each VMA represents a virtually contiguous range with common attributes, and the ranges are organized in an mm_struct. Tasks that share an address space can share that structure. This is Linux kernel terminology and implementation detail, not a definition that applies unchanged to every operating system. See the Linux kernel documentation on process addresses.
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