A: The terms "32-bit" and "64-bit" are commonly seen in system requirements and other technical literature, but few people actually know what these terms mean. Do they refer to hardware or software specifications? What makes a system 64-bit and what is the difference between a 64-bit computer and a 32-bit model? In most cases, you simply need to know if your operating system is 32-bit or 64-bit in order to run a certain program. However, when determining what software to install on your computer, it is helpful to understand what the terms actually mean.
32-bit and 64-bit are commonly used to describe processor architecture or design. A 32-bit processor includes a 32-bit register, which can store 232 or 4,294,967,296 values. A 64-bit processor includes a 64-bit register, which can store 264 or 18,446,744,073,709,551,616 values. Therefore, a 64-bit register is not twice as large as a 32-bit register, but is 4,294,967,296 times larger. That's a big difference, but how does it affect computing performance?
The CPU register stores memory addresses, which is how the processor accesses data from RAM. One bit in the register can reference an individual byte in memory, so a 32-bit system can address a maximum of 4 gigabytes (4,294,967,296 bytes) of RAM. The actual limit is often less – around 3.5 gigabytes – since part of the registry is used to store other temporary values besides memory addresses.
A 64-bit register can theoretically reference 18,446,744,073,709,551,616 bytes, or 17,179,869,184 gigabytes (16 exabytes) of memory. This is several million times more than an average workstation would need to access. What's important is that a 64-bit computer (which means it has a 64-bit processor) can access more than 4 GB of RAM. If a computer has 16 GB of RAM, it better have a 64-bit processor. Otherwise, at least 12 GB of the memory will be inaccessible by the CPU.
While 64 bits is far more storage than what modern computers require, it removes all bottlenecks associated with 32-bit systems. For example, 64-bit systems run more efficiently since memory blocks are more easily allocated. They also support 64-bit instructions and have 64-bit data paths, which enables them to process more data at once than 32-bit systems can.
So how does 32-bit or 64-bit hardware affect software? Generally speaking, 32-bit programs can run on a 64-bit system, but 64-bit programs will not run on a 32-bit system. This is because 64-bit applications include 64-bit instructions that will not be recognized by a 32-bit processor.
In order to run a 64-bit program, your operating system must be 64-bit. Around 2008, 64-bit versions of Windows and OS X became standard, though 32-bit versions were still available. Therefore, if you bought your computer in 2009 or later, there is a good chance you are running a 64-bit operating system. In Windows, you can check your OS version by right-clicking My Computer, selecting Properties, and clicking System to view the system type. If you have a Mac and you are running OS X 10.7 or later, your OS is 64-bit.
While it is possible to install a 32-bit operating system on a 64-bit system, it is best to install a 64-bit version if possible. The 64-bit OS will allow your computer to access more RAM, run applications more efficiently, and, in most cases, run both 32-bit and 64-bit programs.
Exceptions to this rule include system utilities and antivirus programs that are written specifically for a 32 or 64-bit operating system. In these cases, you will need to install the version of the software that corresponds to your OS (which may be different than your hardware). Additionally, device drivers are often written for specific operating systems, so it is important to install 32-bit drivers if you are running a 32-bit OS and 64-bit drivers if your operating system is 64-bit.
Hopefully, the above explanation has give you a better understanding of what 32-bit and 64-bit mean, in reference to hardware and software. If you're installing an operating system, it's important to know what type of processor your computer has, so you can install the right one. If you are installing software, it's important to know what type of operating system your computer is running, so you can install the correct version.
If you have a 32-bit computer, you have no choice but to install a 32-bit OS. If you have a 64-bit system, but have some mission critical peripherals that do not have 32-bit drivers, installing a 32-bit OS might be your best option. In all other cases, it is best to buy 64-bit hardware, install a 64-bit operating system, and run 64-bit applications. This combination will give you the best possible performance.
Updated: January 31, 2014