Please don't post if you don't know what your talking about. You can run a 64bit OS with out a dual core CPU.
I will first discuss 32bit vs 64 bit followed by OS's and last advantages/disadvantages.
What’s 32-bit?
In computer architecture, 32-bit integers, memory addresses, or other data units are those that are at most 32 bits (4 octets) wide. Also, 32-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. 32-bit is also a term given to a generation of computers in which 32-bit processors were the norm.
The range of integer values that can be stored in 32 bits is 0 through 4,294,967,295 or −2,147,483,648 through 2,147,483,647 using two’s complement encoding. Hence, a processor with 32-bit memory addresses can directly access 4 GB of byte-addressable memory.
Now let’s see what 64-bit is:
In computer architecture, 64-bit integers, memory addresses, or other data units are those that are at most 64 bits (8 octets) wide. Also, 64-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size.
Now that we have the differences between 32-bit and 64-bit technologies on the table let’s discuss how they differ. The biggest difference between the two is memory addressing: hence that 32-bit only can directly access memory up to 4 GB, while 64-bits can address memory up to 1000GB or 1 terabyte.
Operating Systems that are 32 bit are limited to approximately 3 to 3.5 GB of ram access.(XP/VISTA). It is the entire design of windows that limits this, and the exact amount is partly determined by your hardware. It has to do with "user mode drivers" in windows. Linux 32 bit can access the full 4 GB of ram.
In addition to being able to access RAM *well* above the 4GB range, there are a few additional system calls in a 64-bit processor that *can* speed up performance a little in some situations ONLY when using a 64-bit operating system.
ALL current "popular" processors from Intel and AMD are 64 bit processors, but 99% of the operating systems in use are 32 bit. Hardware drivers have to be re-written for 64 bit operating systems, and that leads to some hardware problems with 64 bit windows, since not all manufacturers are producing 64 bit drivers for their hardware. (This isn't as much of a problem with 64 bit linux, almost any hardware supported under a 32 bit version, will also be supported under the same 64 bit version.)
ALL "AMD64/EMT64" (AMD's and Intel's 64 bit version of the X86 processors) will FULLY support 32 bit OR 64 bit operating systems.... Meaning a 64 bit processor will run 32 bit software with no problems, but a 32 bit processor (Older P4 CPU's, and older CPU'S) can not run 64 bit software.
Even if you install 64 bit windows, and find hardware drivers for all your hardware, *almost* all windows software you purchase and install will NOT be 64 bit, but will only be compiled as 32 bit versions and will not be able to take advantage of the additional features found in the 64 bit processors. Again, Linux doesn't have this issue, as almost every program in a 64 bit distro is compiled AS a 64 bit executable, so they can take advantage of the full range of commands available in the 64 bit processors.
So basically 32 OS's bit are mostly whats used whats in used, you can use them on any current/new processor. However they are getting outdated for ram. Vista and XP limited to 3 to 3.5 GB of ram access.
The 64 bit OS's are gaining ground biggest advanatage' s are faster and able to address more than 4GB for Vista and XP. Biggest disadvantage is lack of driver. Drivers might work, might not, might be unstable, or their might not be any at all.