So I have just upgraded my laptop from 2GB RAM to 4GB on a 32-bit Vista installation. I may move to 64-bit at some point, possibly as part of an upgrade to windows 7, but my maximum memory use is closer to 3GB than 3 1/2 GB, so there’s just no pressing need at the moment. Or, a 64-bit version of Windows 7 may report that there is only 7.1 GB of usable system memory on a computer that has 8 GB of memory installed. Note The amount of usable memory in the examples are not exact amounts. In computing, the term 3 GB barrier refers to a limitation of some 32-bit operating systems running on x86 microprocessors. It prevents the operating systems from using all of 4 GB (4 × 1024 3 bytes) of main memory. The maximum amount of DRAM that the 32-bit version of Windows 7 Home Basic OS can read is 4GB. The 64-bit version of Windows 7 can read up to 192GB DRAM. The maximum limit of DRAM on the 32-bit version of Windows 8 is also 4GB while the 64-bit version can handle up to 512GB of dynamic random-access memory. On a computer that is running Windows 7, the usable memory (RAM) may be less than the installed memory. For example, a 32-bit version of Windows 7 may report that there is only 3.5 GB of usable system memory on a computer that has 4 GB of memory installed.
When building and running an application under Windows*, you need to be aware of the limitations on the size of code and data your program can declare and use. This article is written for users of Intel C++ and Intel Fortran compilers, but is not specific to those compilers.
In this article, '32-bit' will refer to an application built with a compiler 'for applications running on IA-32', even if it is run on a 64-bit version of Windows. In the Visual Studio* environment, this is a 'Win32' platform target. '64-bit' refers to an application built with a compiler 'for applications running on Intel 64' and run on an 'x64' variant of Windows. In the Visual Studio environment, this is an 'x64' platform target. Appliance owners manuals. Note that 64-bit applications will not run on a 32-bit variant of Windows.
There are three kinds of memory limits:
For more complete information about compiler optimizations, see our Optimization Notice.
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This topic describes the memory limits for supported Windows and Windows Server releases.
Limits on memory and address space vary by platform, operating system, and by whether the IMAGE_FILE_LARGE_ADDRESS_AWARE value of the LOADED_IMAGE structure and 4-gigabyte tuning (4GT) are in use. IMAGE_FILE_LARGE_ADDRESS_AWARE is set or cleared by using the /LARGEADDRESSAWARE linker option.
4-gigabyte tuning (4GT), also known as application memory tuning, or the /3GB switch, is a technology (only applicable to 32 bit systems) that alters the amount of virtual address space available to user mode applications. Enabling this technology reduces the overall size of the system virtual address space and therefore system resource maximums. For more information, see What is 4GT.
Limits on physical memory for 32-bit platforms also depend on the Physical Address Extension (PAE), which allows 32-bit Windows systems to use more than 4 GB of physical memory.
Memory and Address Space Limits
The following table specifies the limits on memory and address space for supported releases of Windows. Unless otherwise noted, the limits in this table apply to all supported releases.
Physical Memory Limits: Windows 10
The following table specifies the limits on physical memory for Windows 10.
Physical Memory Limits: Windows Server 2016
The following table specifies the limits on physical memory for Windows Server 2016.
Physical Memory Limits: Windows 8
The following table specifies the limits on physical memory for Windows 8.
Physical Memory Limits: Windows Server 2012
The following table specifies the limits on physical memory for Windows Server 2012. Windows Server 2012 is available only in X64 editions.
Physical Memory Limits: Windows 7
The following table specifies the limits on physical memory for Windows 7.
Physical Memory Limits: Windows Server 2008 R2
The following table specifies the limits on physical memory for Windows Server 2008 R2. Windows Server 2008 R2 is available only in 64-bit editions.
Physical Memory Limits: Windows Server 2008
The following table specifies the limits on physical memory for Windows Server 2008. Limits greater than 4 GB for 32-bit Windows assume that PAE is enabled.
Physical Memory Limits: Windows Vista
The following table specifies the limits on physical memory for Windows Vista.
Physical Memory Limits: Windows Home Server
Windows Home Server is available only in a 32-bit edition. The physical memory limit is 4 GB.
Physical Memory Limits: Windows Server 2003 R2
The following table specifies the limits on physical memory for Windows Server 2003 R2. Limits over 4 GB for 32-bit Windows assume that PAE is enabled.
Physical Memory Limits: Windows Server 2003 with Service Pack 2 (SP2)
The following table specifies the limits on physical memory for Windows Server 2003 with Service Pack 2 (SP2). Limits over 4 GB for 32-bit Windows assume that PAE is enabled.
Windows 7 Memory Limit 64 BitPhysical Memory Limits: Windows Server 2003 with Service Pack 1 (SP1)
The following table specifies the limits on physical memory for Windows Server 2003 with Service Pack 1 (SP1). Limits over 4 GB for 32-bit Windows assume that PAE is enabled.
Physical Memory Limits: Windows Server 2003
The following table specifies the limits on physical memory for Windows Server 2003. Limits over 4 GB for 32-bit Windows assume that PAE is enabled.
Physical Memory Limits: Windows XP
The following table specifies the limits on physical memory for Windows XP.
Physical Memory Limits: Windows Embedded
The following table specifies the limits on physical memory for Windows Embedded.
How graphics cards and other devices affect memory limits
Devices have to map their memory below 4 GB for compatibility with non-PAE-aware Windows releases. Therefore, if the system has 4GB of RAM, some of it is either disabled or is remapped above 4GB by the BIOS. If the memory is remapped, X64 Windows can use this memory. X86 client versions of Windows don’t support physical memory above the 4GB mark, so they can’t access these remapped regions. Any X64 Windows or X86 Server release can.
X86 client versions with PAE enabled do have a usable 37-bit (128 GB) physical address space. The limit that these versions impose is the highest permitted physical RAM address, not the size of the IO space. That means PAE-aware drivers can actually use physical space above 4 GB if they want. For example, drivers could map the 'lost' memory regions located above 4 GB and expose this memory as a RAM disk.
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