This is a bit pedantic, but x64 refers to Alpha, which existed long before 1999. 64 bit x86 (x86-64, or amd64) wasn’t purchasable until 2003, although it was announced in 2000.

There were several additional shifts between 1978 and 2003:

• 8088 / 8086 has what’s essentially bank switched 16 bit addressing which gives 1 MB, or 2^20 bytes
• 80286 has physical support for 16 megs, or 2^24 bytes
• 80386 has physical support 4 gigs, or 2^32 bytes
• Pentium Pro has PAE support for 64 gigs, or 2^36 bytes
• AMD Opteron from 2003 has support for 1024 gigs, or 1 terabyte, or 2^40 bytes
• Current AMD and Intel CPUs physically support anywhere between 2^48 and 2^57 bytes of physical hardware (256 terabytes to 128 petabytes)

But let’s just use three points of data: 8086 / 8088, 80386, and let’s say the first 64 bit AMD Opteron supports 64 bits:

• 8086 / 8088, 1978, 20 bits
• 80386, 1985, 32 bits
• AMD Opteron, 2003, 64 bits

1978 to 1985 is 7 years, with a change in addressing of 12 bits, or about .6 bits per year.

1985 to 2003 is 18 years, with a change in addressing of 32 bits, or about .56 bits per year. So far, pretty consistent.

How long would it take to go from 64 bits to 128 bits? At around .56 bits per year, that’d be about 114 years, and we’ve had twenty so far.

Check back in 94 years.

There have been a number of 128bit systems over the years.
As it is, 64bit should be good for the life of x86

What are you gonna do with 128 that you can’t do with 64

Lots of good responses regarding why 128-bit isn’t a thing, but I’d like to talk about something else.

Extrapolating from two data points is a folly. It simply can’t work. You can’t take two events, calculate the time between them, and then assume that another event will happen after the same amount of time.

Besides, your points are wrong. (Edit: That also has been mentioned in another response.)

x86 (8086) came out in 1978 as a 16-bit CPU. 32-bit came with the 386 in 1985. x64, although described in 1999, was released in 2003.

So now you have three data points: 1978 for 16-bit, 1985 for 32-bit and 2003 for 64-bit. Differences are 7 years and 18 years.

Not that extrapolating from 3 points is good practice, but at least it’s more meaningful. You could, for example, conclude that it took about 2.5 times more to move from 32-bit to 64-bit than it did from 16-bit to 32-bit. Multiply 18 years by 2.5 and you get 45 years. So the move from 64-bit to 128-bit would be expected in 2003+45 = 2048.

This is nonsense, of course, but at least it’s a calculation backed by some data (which is still rather meaningless data).

Because there is no need from an address space or compute standpoint.

to understand how large 128bit memory space really is; you’d need a memory size larger than all the number of atoms in the solar system

In the rare cases where you need to deal with a 128bit integer or floating, you can do it in software with not that much overhead by concatenating registers/ops. There hasn’t been enough pressure in terms of use cases that need 128bit int/fp precision for manufacturers to invest the resources in die area to add direct HW support for it.

​

FWIW there have been 64bit computers since the 60s/70s.

I think what you need to know, in layman terms, is that 128bit is not the double of 64bit. 65bit is double the amount of 64bit.

128bit is an absurd huge amount. And 64 is so much that even I as a radar engineer do not have to worry about it for a second.

There is very little need for 128 bit computing. And it can be emulated when necessary.

32 bit has only 4 gigabytes which is easily saturated by a single socket computer while 64 bit has 16 million terabytes of addressable possible memory,. you will never see that number ever used in a single socket machine in the history of humanity.

64 bit is quite litterally 2^32 times larger than 32 bit.

There isn’t a need to go to 128 bit yet

Other people have addressed why 64-bit is still fine, but I just want to say that “x86” and “x64” are not two different architectures the way that you’re presenting them. We still use the x86 architecture, it’s just that x86-64, or AMD64, or whatever you want to call it, is a 64-bit extension of that architecture.

And this isn’t the first time that happened; the original 8086 was a 16-bit processor, as was the 286. The 386, however, was a 32-bit processor with backward compatibility for the 16-bit software built for the 16-bit x86 CPUs.

The 386 came out in 1985, so there’s actually a 14 year gap, though actually actually an 18 year gap because a 64-bit x86 processor didn’t actually hit the market until 2003. And then there was a 7-year gap between 16 and 32-bit x86.

But ultimately as other people have said the answer is that we don’t need to go beyond 64-bit right now, and the reason there was such a short gap between 16 and 32-bit processors was because the limitations of a 16-bit architecture became practical obstacles to progress faster than they did for 32-bit, and it’s going to be much longer than that for 64-bit because the address space has grown exponentially, not linearly.

Because it was, vector registers have crazy size today, 1Kb+.

How much memory can you address with 64 bits versus 32 bits? Are we approaching devices with that capacity yet?

Modern CPUs have 512bit registers, and don’t need bigger memory addresses. Not sure what the issue is.

Because 2 to the power of 64 is a stupidly big number.

It is many times less than 2 to the power of 32 because you’ve went ahead and doubled it 32 times to get to 64bits.

What is this? The console wars of the 90s all over again?