When was the first time you needed x64? (i.e. when did you run into the 4GB ram wall?) This year, maybe. Last year at earliest. That's more than a 10 year gap from when a technology was conceived and when it was needed.
To be fair, Moore's Law describes an exponential change in usable address space that we're still living through.
The numbers are kind of spooky. The stupidest statement of Moore's Law is "everything doubles in size, at constant cost, every 18 months." If we take that statement literally, and also assume that the reaching of the "32-bit memory wall" became a widespread phenomenon around, say, 2009 [1], a backwards extrapolation suggests that the RAM industry should have begun in 1961 with a single byte. This is frighteningly close to agreeing with actual history. [2]
The implication is that another 32 bits only buys us another 48 years. After that we'll need a 128-bit address space in order to properly index our personal catalogues of everything ever. [3]
Or, perhaps, at some point we will just get tired of making RAM.
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[1] This is when I first noticed it. Yeah, people with millions of dollars hit this wall in 1990. Must have been nice to be them.
You will note a certain degree of slight-of-hand in my numerology here. ;)
[2] Intel's first memory product was a 64-bit unit in 1969. In the fantasy modpunk universe where Moore's Law was operating during the Sixties, that would imply a starting point of a single bit in 1960.
If we reject my narcissistic assertion that nobody important cared about the 32-bit memory wall until this year, and instead accept oomkiller's assertion that the 32-bit memory wall first appeared on the radar around 1990, that would push back the birthday of the first bit to around 1941. I give you Wikipedia:
The [Zuse] Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.
Cue the Twilight Zone theme.
[3] We probably won't need that 256-bit address space in 100 years, since there are estimated to be only 2^266 atoms in the observable universe.
What AMD did (and Intel subsequently copied) with x86-64 was to significantly drop the price of 64-bit capable hardware, to the point where it shipped on personal workstations which didn't really need it then.
http://en.wikipedia.org/wiki/X86-64#Virtual_address_space_de...
This performance improvement, more so than the ability to address more than 4gb of memory, is the primary reason for 64-bit processing becoming mainstream, in my opinion.