As noted in Processers The x86 Family, the span of 37 years lead to 32-bit increase in addressing space from 1976 to 2013 we have 16-bit addressing to 48-bit addressing. This gives an average of about 1-bit per year, or 8-bits per year. Thus, it is reasonable that 2020 would be the year when it increase to 56-bit address space and 2028 to be the year when 64-bit address space would be complete.
What does this tell us? We need to plan in a way so that every 4 years, an increase in 4-bits of address space should occur.
AMD takes the lead after Intel attempts an alternative 64-bit processor instead of continuing the x86 family.
AMD's x86-64 normally shorten to x64 does not allow 16-bit instructions in the 64-bit mode. Thus, only 8-bit, 32-bit, and 64-bit instructions are available. Only 32-bit applications with 32-bit and 8-bit instructions are compatible.