The difference between 64 and 32 bit processors

What are bits?

The number of bits in a processor refers to the size of the data types that it handles and the size of its registry. A 64-bit processor is capable of storing 264 computational values, including memory addresses, which means it’s able to access over four billion times as much physical memory than a 32-bit processor! The key difference: 32-bit processors are perfectly capable of handling a limited amount of RAM, and 64-bit processors are capable of utilizing much more. Of course, in order to achieve this, your operating system also needs to be designed to take advantage of the greater access to memory. This Microsoft page runs down memory limitations for multiple versions of Windows.

 

How many bits?

As a general rule, if you have under 4 GB of RAM in your computer, you don’t need a 64-bit CPU, but if you have 4 GB or more, you do. While many users may find that a 32-bit processor provides them with enough performance and memory access, applications that tend to use large amounts of memory may show vast improvements with the upgraded processor. Image and video editing software, 3D rendering utilities, and video games will make better use of a 64-bit architecture and operating system, especially if the machine has 8 or even 16 GB of RAM that can be divided among the applications that need it.

Through hardware emulation, it’s possible to run 32-bit software and operating systems on a machine with a 64-bit processor. The opposite isn’t true however, in that 32-bit processors cannot run software designed with 64-bit architecture in mind. This means if you want to take full advantage of your new processor you also need a new operating system, otherwise you won’t experience any marked benefits over the 32-bit version of your hardware.

Operating System Differences

With an increase in the availability of 64-bit processors and larger capacities of RAM, Microsoft and Apple both have begun to develop and release upgraded versions of their operating systems that are designed to take full advantage of the new technology. In the case of Microsoft Windows, the basic versions of the operating systems put software limitations on the amount of RAM that can be used by applications, but even in the ultimate and professional version of the operating system, 4 GB is the maximum usable memory the 32-bit version can handle. While a 64-bit operating system can increase the capabilities of a processor drastically, the real jump in power comes from software designed with this architecture in mind.

Software and Drivers

Applications with high performance demands already take advantage of the increase in available memory, with companies releasing 64-bit versions of their programs. This is especially useful on programs that can store a lot of information for immediate access, like image editing and software that opens multiple large files at the same time.

Video games are also uniquely equipped to take advantage of 64-bit processing and the increased memory that comes with it. Being able to handle more computations at once means more spaceships on screen without lagging and smoother performance from your graphics card, which doesn’t have to share memory with other processes anymore.

Most software is backwards compatible, allowing you to run applications that are 32-bit in a 64-bit environment without any extra work or issues. Virus protection software and drivers tend to be the exception to this rule, with hardware mostly requiring the proper version be installed in order to function correctly.

Mathematically:

A bit is short for “binary digit.” It is basically how a computer stores and makes references to data, memory, etc. A bit can have a value of 1 or 0, that’s it. So binary code is streams of 1’s and 0’s, such as this random sequence 100100100111. These bits are also how your processor does calculations. By using 32 bits your processor can represent numbers from 0 to 4,294,967,295 while a 64-bit machine can represent numbers from 0 to 18,446,744,073,709,551,615. Obviously this means your computer can do math with larger numbers, and be more efficient with smaller numbers.

Now see, that description wasn’t too bad, but the question is how does this affect you, the average PC owner? The largest benefit will go to academic institutions and private companies, where large calculations are being performed, huge databases are being accessed, and complex problems are being solved.

There is one significant disadvantage of 64-bit processors when compared to 32-bit processors: minimum operation size for calculations. A 64-bit processor must do all integer calculations using a 64-bit wide register (that is, all integers must be represented as 64 bits in size). A 32-bit processor does all integer calculations in 32-bit sizes. While performing the actual calculation (e.g. adding two numbers) is neither faster nor slower under 64 vs 32 bit systems, the requirement to pull full 64-bit chunks from memory to do any calculation results in more memory "pressure" than a 32-bit processor. 

The result of this is that for a system which does mostly smaller integer calculations (i.e integers which are 2³¹ or small in size), a 32-bit system will have about HALF the memory bandwidth requirement of a 64-bit system. A memory latency is the the dominating factor in modern CPU performance (i.e. the time to get data from memory is far greater than the time to perform a calculation on that data), a 32-bit processor will perform noticeably faster doing such smaller calculations than a 64-bit processor. 

A related disadvantage of a 64-bit CPU vs a 32-bit CPU is that the larger operational unit (word) size means that all pathways, registers, and memory units attached to a 64-bit CPU have to be about double the size as required in a 32-bit CPU. This results in about a 40% larger number of transistors required to implement a (roughly) equivalent 64-bit processor vs a 32-bit processor. This does not translate into a 40% higher cost, but does significantly increase production costs; it also significantly increases the thermal profile of the processor (i.e the larger number of transistors requires more power and produces more heat).

Everyone that doesn’t fall into that category will see some benefit of using 64 bit processors over 32 bit processors, but not much in today’s marketplace. The AMD Athlon 64-bit processor is completely backward compatible, meaning you can currently use it with 32-bit operating systems and software programs. You will see some benefits by using this setup, but because the programs weren’t written to take advantage of the extra power, they won’t use much of it.

The true benefits of this set up don’t come from the amount of bits, but by the improved structure of the 64 bit vs 32 bit processor's older structure. A 64-bit processor is made with more advanced silicon processes, have more transistors, and faster speeds. This is currently where the true benefit of switching to a 64-bit processor lays.

As for 64-bit operating systems and software, many are in the works, but nothing is in final version. Microsoft has released a beta version of Windows XP that takes advantage of the 64 bit technology, but there are still issues. The problem is when you run 32-bit software programs in the environment of a 64-bit operating system. Many programs won’t work properly, such as Adobe Acrobat and Windows Media Player, for example. Another issue is RAM. You really need about 4 GB of RAM to take full advantage of the capabilities offered by a 64-bit processor, while most PC owners have less than 1 GB under their computer’s hood.

So, the question now is should you buy a 64 bit processor now, or wait?

Disadvantages:

You’re currently not able to take full advantage of the technology because the software vendors haven’t made the switch from 32-bit to 64-bit processors.

Most AMD Athlon 64 bit processors are expensive, with prices sure to go down in the future.

Advantages:

Better performance out of a 32-bit operating system.

Probably the last processor you’ll have to buy for many years to come.

You’ll be the talk of all your friends!
As you can see, a sound argument can be made for both cases. You’ll have to determine if the differences will benefit your situation and computing future. I’ll leave the ultimate decision up to you.