Looking at the iPad Mini, it’s hard not to be impressed. Here, we have a machine that packs in the specs of the iPad 2 into a machine with a 7.9 screen. Both tablets have a 1,024 x 768 resolution, but that means that with a smaller size, the Mini has better clarity at 162ppi than it’s iPad 2 brother at 132ppi. They’re still nowhere near the 264ppi of the Retina-iPad, but that’s not too shabby, regardless.

Inside the iPad Mini, Apple’s dual-core A5 processor reigns supreme, and at least owners of the iPad 2 know they won’t miss out on future upgrades for a couple more years thanks to a new machine sharing the same innards and holding off Apple’s forced upgrade cycle a little longer.

There’s a 10 hour battery (roughly), Bluetooth, WiFi, option for 3G and 4G over nanoSIM, and that new Lightning dock connector, plus a whole lot of engineering that lets Apple force all of this into a smaller body crafted out of one piece of machined aluminium.

At 7.2mm, it’s quite thin, especially compared with the 8.8mm thin iPad 2, 9.4mm thin new iPad, and plethora of iPad competitors from other manufacturers ranging from 7.7mm to 10mm.

But what could Apple do to make the iPad even thinner?

Obviously, technology will shrink, and when that happens, it will be reorganised and made to work in a better configuration, but there does seem to be a limit to how thin we can make multimedia devices, and that’s roughly between the 4 and 5mm thickness range, barely two millimetres thinner than what’s currently possible.

Why?

Until Apple – and the rest of the manufacturers out there – are able to remove the headphone jack and ask you to use Bluetooth headphones only, it’s going to be hard to push much further on the thickness.

Every 3.5mm jack we’ve seen measures roughly 4mm across, and while companies can design around it and try to shave elements off the side, the fact is the headphone jack requires both length and some thickness.

There’s not much getting around this: we depend on the 3.5mm headphone jack. Would you buy anything without it?

Roughly a decade ago, mobile manufacturers tried to tackle this problem ahead of time with the ill-fated 2.5mm headphone jack, a smaller and thinner version of its brother that virtually no headphones supported, except those bought with a mobile at the time. We can remember them on iMate and Nokia handsets, and even remember buying adaptors that wouldn’t feel very good in the pocket just so we could listen to the music on our phones with the headphones of our choice.

The 2.5mm "standard"

No one really bought into the 2.5mm headphone jack, and it gradually disappeared, to be replaced with the 3.5mm headphone standard. Microsoft still uses some form of it on its Xbox 360 controllers, but it’s not mainstream enough for people to be concerned.

So here we are with 3.5mm, the friend of any headphone lover as, well, it’s the adaptor your pair will pretty much always come with. This is also one of the main things holding back the thickness, and stopping manufacturers from culling the size much more.

In the next few years, as miniaturisation continues and the casing become stronger, lighter, and amazingly thinner, we’ll still see the gadgets drop to thickness levels that seem even more impressive, but until we ditch the 3.5mm headphone jack, that wafer thin credit card tablet is just ever so slightly out of reach.