I remember all those video game boxes stamped with IBM PC (and compatible), while bringing good memories I felt this was rather incorrect.
Most of these games would never run on such computers, i.e. they display 256 colors, output audio on sound cards and most importantly, have much higher CPU requirements; technologies that surfaced during AT era.
Since the natural descendants of the PC are the XT then the AT, I believe that our PCs are in fact ATs, is that correct ?
First of all, the original IBM PC is capable of much more than is commonly believed, although that didn’t help with games back in the day of course (and the effects in that demo aren’t necessarily usable in a game anyway).
That’s not all that relevant to your actual question though. What is relevant IMO is the fact that game publishers were quite careful to document the real requirements of their games; see for example this 286+ game (Willy Beamish) or this 386+ game (The 7th Guest). This was important even in the early PC days: the very first PC itself existed in a variety of configurations, with different graphics adapters (commonly MDA, CGA, and then Hercules) and different amounts of memory. So stating that something required an “IBM PC (or compatible)” was never sufficient to know that any given computer would be able to run a specific piece of software...
Many would argue that PC gaming only came into its own with the advent of the 386, VGA and sound cards, none of which were present in the “official” IBM PC AT. Back in those days people certainly differentiated AT-class computers from 386-class computers, so saying that “PCs are in fact ATs”, while correct in some ways, would have been considered misleading in others even when ATs were still (somewhat) relevant.
It’s also worth considering that our PCs are now far, far removed from ATs, even if they’re still backwards-compatible with them (and even then, not for much longer). So “our PCs are in fact ATs” has become less and less true with time, and is now pretty much irrelevant.
Since the natural descendants of the PC are the XT then the AT, I believe that our PCs are in fact ATs, is that correct ?
No. If at all, they are PC-Standard Computers, as this group, lead by Intel andMicrosoft was the only standard body trying to define and standardize the advancements.
In terms of compatibility thay are no longer defined by some hardware API (*1), but software API's - thanks to an ever increasing CPU power enabeling the encapsulation of hardware to a great extend. The last of these common standards is the PC-2001 from, well, 2001. One reason for not adding any newer is that the 2001 standard did not only cover next to all common user related interfaces (and removal of obsolete), but also is seen as the point where the Legacy-Free-PC came to be.
It was based on the fact, that individual interfaces where no longer developed. Standards like PCIe and USB covering all I/O connections with new deviced only added thru one of these. All together hiden by multiple levels of API - just this time way too complex for average programmers to hack around :)
*1 -in fact, the PC was never realy to be defined by hardware, it was just badly written software bypassing abstraction layers that resulted in hardware dependance.
Today's "PCs" (as in Windows/Linux/... x86-64 box) have little in common with an IBM AT. There's still some compatibility on the software level but the hardware is vastly different.
Even several successors of these vanished interfaces have gone:
Even the AT's BIOS that has incredibly long worked as a core for later BIOSes is increasingly replaced by UEFI.
Anything substantial left?
A good metric of whether PCs still exist might be whether such a computer can run MS-DOS (or better, the successor OpenDOS which is actually still maintained). The answer for many of the computers we have in front of us right now would be yes. (There would be some hardware incompatibilities, as DOS drivers don't exist for a lot of hardware, but the machines would run, and some software could be loaded and executed.)
Other posters have clarified on the differences between the XT and the AT. I have always casually thought of the XT as 8088/8086-class machines and the AT as being 80286-class machines, and if that's a reasonable line of thinking (and I think it is), anything 80386-based and newer stopped being a PC AT, even if it would satisfactorily run AT software. (Bear in mind that the actual AT ran almost all XT software just fine, too.)
