32-bit versus 64-bit Operating Systems and Software


For desktop and laptop computer users, leaving aside the subject of the different types of CPU (Central Processing Unit) made by various manufacturers and the issues created by large-memory video cards in computers designed for gaming, the question often arises about the difference between a 32-bit and a 64-bit OS (operating system) and application software. To run a 64-bit CPU you must have a 64-bit motherboard. The operating system can then be either 32-bit or 64-bit. You cannot install a 64-bit-OS on a motherboard with a 32-bit CPU.

Operating Systems

A 32-bit Windows OS can only address 4 GB of RAM and splits that memory, allocating 2 GB of memory to the kernel and up to 2 GB of memory to each application’s private address space. After that, the OS uses a paging file on the hard disk drive. There is a technology called 4GT[1] that may be used on certain 32-bit systems to allow applications to access up to 3 GB of memory by reducing the amount available to the OS. Also there are some applications than can run PAE X86[2][3] on certain Windows 32-bit systems to allow access to more than 4 GB memory. When memory requirements exceed the installed RAM, the OS uses a paging file on the hard disk drive, which is much slower.


The main advantage of a 64-bit OS is its ability to address more RAM. Without getting into all of the technicalities, the calculations are as follows:

The amount of memory that can be accessed by a 32-bit OS is:
232 = 4,294,967,296 bytes, or 4,294,967,296 / (1,024 x 1,024) = 4,096 MB = 4 GB
The amount of memory that can be accessed by a 64-bit OS is:
264 = 18,446,744,073,709,551,616 bytes, or 18,446,744,073,709,551,616 / (1,024 x 1,024) = 16 EB

The 64-bit value of 16 EB (exabytes) is very large and at present is only a theoretical consideration. If we think in kilobytes 1 kB = 1000 bytes, then 1 MB = 10002 bytes, 1 GB (gigabyte) = 10003 bytes, 1 TB (terabyte) = 10004 bytes, 1 PB (petabyte) = 10005 bytes, and 1 EB (exabyte) = 10006 bytes. 16 EB of RAM seems like a ceiling that may never be reached, but when earlier computers were running with 16-bit architecture such as MS-DOS and early Windows versions (Windows 3.x), the memory limit was 64 kB and now many of us have at least 4,000,000 kB!

32-bit and 64-bit Operating Systems and Application Software Compatibility

Without using a special emulation, you cannot run 64-bit applications on a 32-bit OS, whereas you can run 32-bit applications on a 64-bit OS. In the case of Windows, it uses WOW64, an x86 emulator that allows 32-bit Windows-based applications to run on 64-bit Windows. WOW64 is provided with the operating system and does not require enabling. The potential compatibility of various arrangements is shown in the table below.

Compatibility of a 64-bit CPU with the OS and Application Software
CPU (Processor) 64-bit
OS (Operating System) 64-bit 64-bit 32-bit 32-bit
Application Programme 64-bit 32-bit 32-bit 64-bit
Yes Yes Yes No

Operating system memory limitations

In practical terms and depending on the OS version and other hardware considerations such as the motherboard and CPU, a 64-bit OS can address much more memory than the 32-bit versions and the maximum installable memory for various Microsoft 64-bit systems are as follows:

Windows XP: 128 GB (support ended 8 April, 2014);
Windows Vista: Home Basic: 8 GB; Home Premium: 16 GB; Professional, Enterprise, Ultimate: 128 GB (support to end 11 April, 2017);
Windows 7: Home Basic: 8 GB; Home Premium: 16 GB; Professional, Enterprise, Ultimate: 192 GB;
Windows 8: 128 GB; Windows 8 Professional, Enterprise: 512 GB;
Windows 10: 128 GB; Windows 10 Professional, Education, Enterprise: 2 TB.

Depending on the CPU, the OS on Windows 64-bit servers can access memory as follows:

Windows Server 2003: 2 TB,
Windows Server 2008: 2 TB,
Windows Server 2012: 4 TB,
Windows Server 2016: 24 TB.

Software memory requirements

Applications software have the same memory limitations as operating systems. Anyone who has processed multimedia files such as large graphics or video files will have encountered memory issues on computers with limited memory. The programme will slow down when it is forced to use the paging file.

For many of the latest versions of applications, the software can be obtained in the 64-bit versions as well as the 32-bit versions. Photoshop CS6 can be used with only 2 GB of RAM on a 32-bit OS, but even with 4 GB RAM installed, it can only access about 3 GB RAM. When using a 64-bit OS, 8 GB of RAM is recommended. Although 2 – 3 GB of RAM can be used to a limited extent for software such as ANSYS for the FEM (Finite Element Method) to do engineering analyses when using a 32-bit OS, the recommended RAM when using a 64-bit OS is 12 – 24 GB.

If advice is needed in the selection of hardware, operating systems or applications, where the choice of 32-bit or 64-bit is an issue, we would be pleased to provide assistance. Please note that we do not sell hardware or software, but can write the specifications to allow you to obtain suitable hardware and software to meet your requirements.

1. 4GT or 4GT RAM Tuning is a 4-gigabyte tuning feature that can be enabled on some systems such as Windows Server 2000, Windows Server 2003 and Windows XP on a 32-bit hardware platform. It increases the virtual address space that is available to certain applications up to 3 GB, and reduces the amount available to the system to between 1 and 2 GB.
2. PAE X86 or Physical Address Extension X86 allows servers running Windows Server 2003, Enterprise Edition, and Windows Server 2003, Datacenter Edition, on a 32-bit hardware platform to access physical memory beyond 4 GB. To do this, PAE changes the memory addressing from 32-bit addressing mode to 64-bit addressing mode, allowing the operating system and high performance drivers and applications access to the additional physical memory. When using the larger amount of physical memory made available by PAE X86, operating system performance can be increased, particularly when the server is hosting multiple applications. Applications can also have direct access to the physical memory beyond 4 GB provided they use the Address Windowing Extensions (AWE) API set.
3. Further research has uncovered that there is a patch that can be applied to Windows Vista SP2, Windows 7 SP0, Windows 7 SP1, Windows 8 and Windows 8.1, which will allow running PAE on 32-bit versions of these operating systems. Although theoretically you can address up to 64 GB of memory in PAE mode, each process is limited to 2 GB of memory space per active process. Note also that certain hardware drivers might not work correctly in PAE mode and there may be some display issues. However, this may be a stopgap solution for some users needing more memory, but stuck with a 32-bit OS.

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