What's Different About 64-Bit?
While 32 bits of information can only access 4 GB of RAM, a 64-bit machine can access 17.2 BILLION gigabytes of system memory, banishing any limits far into the future. This also means that your video cards and other devices will not be stealing usable memory space from the operating system. Windows 64-bit Home editions are still limited to 16 GB of RAM for licensing reasons, but the Professional and Ultimate versions can use up to 192 GB of RAM, so keep that in mind when building that killer system.
The per-process limit is also greatly increased—on 64-bit Windows, instead of a 2 GB limit, each application has access to 8 TB of virtual memory without any special API, a huge factor when you consider applications like video editing or virtual machines that may need to use enormous amounts of RAM.
On Windows, the 64-bit versions also come with a technology to prevent hijacking the kernel, support for hardware-enabled data execution protection, and mandatory digitally signed 64-bit device drivers. You also won't be able to use your 16-bit apps anymore, which hardly seems like a loss.
