There’s been a lot of talk about a seven-inch “iPad mini” over the last 18 months or so. The rumors, while compelling to many, never really resonated with me, and I’ve dismissed them countless times in the past. After all, what possible strategic reason could Apple have to offer such a thing? It’s not like the Kindle Fire’s affecting iPad sales (at all), and competition from the Android crowd is practically nonexistent. There’s simply no obvious impetus for Apple to take on the added labor and manufactory costs necessary to shrink down the iPad, especially when it can’t even keep the big version in stock!

But then the rumor got specific — a little too specific.

Back in December, DigiTimes’ Max Wang wrote of “industry sources” who claimed the so-called iPad mini would not merely fill some uncertain spot in the seven-inch range but would actually feature a definite 7.85-inch display. We picked up the story (as did many others), but it didn’t generate more than a ripple of fleeting interest. However, in the several months since, that ripple’s started to resonate, and now it’s making waves.

Two weeks ago, a Samsung executive with inside knowledge of Apple’s affairs repeated the all-but-forgotten 7.85-inch iPad mini rumor, and same-day (re)reports of contracted display manufacturers added considerable volume to the mini mania.

Still, rumors are just rumors, and they aren’t particularly convincing in and of themselves. It doesn’t matter how many sources echo some generic sentiment. What does matter is a rumor’s singular specificity. In this case, it’s that pesky 7.85 inches.

And what makes everything even more convincing is that the leaky sources never sought to explain why that number’s so darned significant!

So, allow me.

Ahem.

Because the original iPad screen was set at a pixel resolution of 1024 x 768, it’s a good guess that the mythical iPad mini — in order to simplify and streamline third-party development as much as possible — will need to sport that same resolution (or, like the new iPad, a multiple thereof). Of course, the entire proposed point of the mini is to keep production costs low enough to hawk it for between $250 and $300, which pretty much means no Retina display. So, 1024 x 768 will have to do.

And, boy, does it ever. If you do the math, a 7.85-inch tablet with a resolution of 1024 x 768 works out to a PPI of 163. 163!

163 PPI!

So what?

So this: That’s the exact same resolution as the pre-Retina iPhone/iPod touch display!

Consider: When it comes to fabricating LCD panels, the density of a given screen’s pixels is inexorably tied to the manufacturing process itself. In other words, working at a given resolution, a screen-maker can manufacture whatever size of display it likes using existing assembly-line hardware. However, if said maker should change the intended resolution, much of that line must be changed as well. And that is an extremely expensive process. Luckily, Apple and its manufacturing partners — who’ve been making original spec iPhone and iPod touch screens for almost five years now — have all the machinery they need to make 163 PPI displays, and costs to do so are cheaper than ever. If the iPad mini comes to fruition, it will house Apple’s least expensive LCD panel (after the iPhone 3GS, which is due to be discontinued this year) — especially if, like the current iPod touch, it doesn’t include wide-angle IPS technology.

And it gets better. Just like a 7.85-inch iPad mini aligns perfectly with existing manufactory hardware, its 1024 x 768 screen aligns just as well with existing iPad apps! Developers wouldn’t need to provide Apple with a third distinct set of layout parameters; the iPad mini would simply (and automatically) resize their iPad apps to fit its smaller screen. This is a painless, easy solution to a potentially back-breaking problem.

Now, I know what you’re thinking: Wouldn’t iPad apps be impossible to use on a smaller screen? Wouldn’t shrinking down those menu options and corner toggles and browser tabs make them irritatingly difficult to consistently touch? Well, in a word, no. At least, not at 7.85 inches.

See, when Apple was designing its first iPhone (circa 2006), company engineers determined through testing that the minimum comfortable size for an interactive element on a touchscreen display is 44 x 44 pixels. Anything smaller would yield erratic results. The pixel density used to arrive at this number, naturally, was that used in the first iPhone — again, 163 PPI. (Note that with the advent of the Retina display, the term “points” is used instead of “pixels.” However, Apple’s Human Interface Guidelines still call for a direct equivalent based on the original measurement. For example, the new iPhone 4/4S HIG has its interactive minimum set at 44 x 44 points, which is 88 x 88 pixels.) In layman’s terms, all this simply means that no app has tappable input zones smaller than Apple’s approved dimensions. Whatever the size of a given menu option in a given iPad app, it cannot shrink beyond Apple’s pre-established minimum. It might take a bit more hand-eye coordination, but overall interaction should not be affected.

With all the potential technical drawbacks disproved, what other obstacles remain for the iPad mini’s run to production?

At this point, none. Apple already sells its iPod touch for as little as $199, and, considering the apparent ease with which Cook and company can have iPad mini screens made, they ought to be able to keep the small tablet’s MSRP similarly competitive.

To be sure, Apple doesn’t need to add another device category to its iOS family. But Apple makes its money primarily through selling hardware. The more people it draws into its ecosystem, the more hardware it’s going to sell. Folks who want an iPad — and, most importantly, can afford an iPad — will buy one. Selling a less expensive, smaller (but still manageably large) tablet will neither cannibalize iPad sales nor displace the need for the iPod touch, and it opens a big door for anyone who wants the true iPad experience but doesn’t have true iPad money. It’s a win-win scenario.

While Apple can pretty much afford anything, it can’t afford not to make the iPad mini.

Apple will release a 7.85-inch tablet later this year. And yes, it’s going to be called the iPad mini. It may or may not have the “skinny” bezel everyone’s been talking about, but two things are crystal clear: It’ll sport a 163 PPI 1024 x 768 display, and lots of folks are going to buy it.

Intel, you better buckle up. Amazon, you have my condolences. Windows 8, we hardly knew ye.