Some of you may be as old as me and remember that you could get Windows XP in two versions, the Standard "32Bit" version which meant you could only run a maximum of 4GB of ram and even that would only show up as 3.2GB, or you could have "Windows XP 64Bit" that would only run on your name sake
@AthlonXP1800 or any variant Athlon XP and you could run as much RAM as you liked.
Being able to run practically infinite RAM was more a by-product of that 64Bit architecture but that and much besides is what made it so successful, AMD was actually late to the 64Bit race that was going on at the time and had been for a few years, Intel for example was already developing Itainium, like all other attempts by the rest of the CPU industry at the time it didn't actually work and they couldn't get it to work.
AMD's version did, it worked really well and it was easily portable from X86, so it was adopted by the industry.
Originally Intel had licenced X86 to AMD because IBM wanted a second source for Intel CPU's, AMD used to make Intel CPU's, why you might ask didn't AMD design and make their own CPU's? eventually they did, AMD's own X86 designs ended up being better than Intel's, AMD started gaining market share, a lot of it, Intel threatened not to renew AMD's X86 licence, as they are entitled to do but that's when AMD entered the 64Bit race and made it so that it was also X86 compatible, Intel tried to get Itainium to work refusing to give up on it but eventually realised that if they didn't adopt AMD64 they would be out of business entirely, so they agreed AMD could keep X86 with Intel getting AMD64 in return.
After that Intel started paying large OEM's not to use AMD CPU's at all, other than creating X86 it was the only other thing that Intel did and was successful in.
Multicore X86 Processors is another thing Intel tried and failed in where AMD succeeded and Intel now licence, your Intel CPU is architecturally an AMD CPU with an Intel logo on it, ironically when you think back to that ^^^.