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Answer: In computing, 32-bit and 64-bit are two different types of processors. The bit number (usually 8, 16, 32, or 64) refers to how much memory a processor can access from the CPU register.
Most computers made in the 1990s and early 2000s were 32-bit machines. A 32-bit system can access 232 (4,294,967,296) memory addresses. Practically speaking, a 32-bit computer is limited to accessing 4,294,967,296 bytes (4 GB) of RAM. Since most computers released over the past two decades were built on a 32-bit architecture, most operating systems were designed to run on a 32-bit processor.
▶ Around 2008, 64-bit processors became mainstream and personal computers starting including 64-bit CPUs. Therefore, popular operating systems, such as Windows and Mac OS X began shipping in both 32-bit and 64-bit editions, which allowed them to run on either 32 or 64-bit hardware.
While a 32-bit processor can access 232 memory addresses, a 64-bit processor can access 264 memory addresses. This is not twice as much as a 32-bit processor, but rather 232 (4,294,967,296) times more. This means a 64-bit machine could theoretically access 18,446,744,073,709,551,616 memory addresses or more than 18 billion GB of RAM. However, as of 2013, there are few computers that can physically support more than 64 GB of RAM.
While many 32-bit programs can run on a 64-bit operating system (OS), 64-bit programs are not compatible with 32-bit operating systems. Additionally, many 32-bit drivers and system utilities are incompatible with 64-bit systems. Therefore, when purchasing or downloading new software, it is important to know if a 32-bit or 64-bit OS is installed on your computer.
