It was considered a luxury until about nineties, and existed perhaps only in places where it was required by technology (e.g. big iron computer rooms). Then we started getting summers where the temperature could hit 40 C and extend into six-week draughts. This century, they're, like, everywhere. Even the most solidly built houses can't withstand more than three weeks of the hottest part of the summer, unless it's a peasant's adobe house with 60 cm thick walls, which stays cool forever.
There are no central units on sale, no air ducts. Everybody hangs the outside unit somewhere on the façade and the inside unit nearby on the same wall, so the condensation tube and the freon tubes go through the same hole. Nowadays every majstor will pull a hose to the ground or into the nearest gutter, but the older units may be mounted without a hose and may drip from above onto the sidewalk, so watch for wet spots when walking in the summer. If it's wet while it's dry everywhere else, it's probably dripping. Not much, the air isn't humid in the summer.
The units that are mounted in the window aren't popular, because the guillotine windows are pretty much nonexistent. The windows have hinges here.