Well, it supports 64-bit instructions, that means you can use it with 64-bit Operating System and install more then 4 gigabyte memory. Basically with nowadays technologies not many applications support 64 bits, so the only advantage is that the OS can see and use more than 4 gigs of RAM. In contrary if install on 32 bits system 4Gigabytes of RAM, it can use only 4Gig minus 640 Mbytes so it sees arround 3.28 Gigabytes. It used mostly on servers. 
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386DX was the Intel chip which was first to support a 32-bit bus architecture.
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