Virtual address space
 | This article relies largely or entirely on a single source. (August 2012) |
In
Example
- In the following description, the terminology used will be particular to the Windows NT operating system, but the concepts are applicable to other virtual memory operating systems.
When a new application on a
0 4 GiB VAS |----------------------------------------------|
Then the application's executable file is mapped into the VAS. Addresses in the process VAS are mapped to bytes in the exe file. The OS manages the mapping:
0 4 GiB VAS |---vvv----------------------------------------| mapping ||| file bytes app
The v's are values from bytes in the
kernel32.dll and user32.dll):
0 4 GiB VAS |---vvv--------vvvvvv---vvvv-------------------| mapping ||| |||||| |||| file bytes app kernel user
The process then starts executing bytes in the EXE file. However, the only way the process can use or set '-' values in its VAS is to ask the OS to map them to bytes from a file. A common way to use VAS memory in this way is to map it to the
0 4 GiB VAS |---vvv--------vvvvvv---vvvv----vv---v----vvv--| mapping ||| |||||| |||| || | ||| file bytes app kernel user system_page_file
And different parts of the page file can map into the VAS of different processes:
0 4 GiB VAS 1 |---vvvv-------vvvvvv---vvvv----vv---v----vvv--| mapping |||| |||||| |||| || | ||| file bytes app1 app2 kernel user system_page_file mapping |||| |||||| |||| || | VAS 2 |--------vvvv--vvvvvv---vvvv-------vv---v------|
On Microsoft Windows 32-bit, by default, only 2 GiB are made available to processes for their own use.[2] The other 2 GiB are used by the operating system. On later 32-bit editions of Microsoft Windows, it is possible to extend the user-mode virtual address space to 3 GiB while only 1 GiB is left for kernel-mode virtual address space by marking the programs as IMAGE_FILE_LARGE_ADDRESS_AWARE and enabling the /3GB switch in the boot.ini file.[3][4]
On Microsoft Windows 64-bit, in a process running an executable that was linked with /LARGEADDRESSAWARE:NO, the operating system artificially limits the user mode portion of the process's virtual address space to 2 GiB. This applies to both 32- and 64-bit executables.[5][6] Processes running executables that were linked with the /LARGEADDRESSAWARE:YES option, which is the default for 64-bit Visual Studio 2010 and later,[7] have access to more than 2 GiB of virtual address space: up to 4 GiB for 32-bit executables, up to 8 TiB for 64-bit executables in Windows through Windows 8, and up to 128 TiB for 64-bit executables in Windows 8.1 and later.[4][8]
Allocating memory via
Linux
For x86 CPUs, Linux 32-bit allows splitting the user and kernel address ranges in different ways: 3G/1G user/kernel (default), 1G/3G user/kernel or 2G/2G user/kernel.[9]
See also
- Linear address space
- Single address space operating system
Notes
- ^ "What is an address space?". IBM. Retrieved May 5, 2024.
- MSDN. Microsoft.
- MSDN. Microsoft.
- ^ MSDN. Microsoft.
- MSDN. Microsoft.
- MSDN. Microsoft.
- MSDN. Microsoft.
- MSDN. Microsoft.
- ^ "Linux kernel - x86: Memory split".
References
- "Advanced Windows" by Jeffrey Richter, Microsoft Press