Let's kick off with a quick question: how many active OS X users do you think there are in the world today? 10 million? 15 million? 20 million at a push?

How about 75 million and counting?

Apple's Phil Schiller dropped that bombshell at the Worldwide Developer Conference (WWDC) last June and that number's sure to have soared since then.

Why? Because that 75 million figure includes iPhone and iPod touch users. Pretty soon it'll include iPad users, too.

The numbers are significant for a couple of reasons: 1. it's putting Apple's operating system in front of millions of people who've never gone near a Mac before and 2. the iPhone OS and iPad OS are part of a growing OS X family, of which Mac OS X is part. So what should that tell us about the next version of Mac OS X?

Snow Leopard synergies

Fundamentally, the three OS X variants already have much in common – they are all based on a Darwin core with a Cocoa framework and Apple technologies such as Core Animation, Core Image, Core Video and Core Location.

It's a two-way street. The underpinnings of the iPhone and iPad operating systems are based on the same stuff that powers Mac OS X, but it also works the other way around - QuickTime X on Snow Leopard is the direct result of enhancements needed for QuickTime on Phone.

iPhone OS features have appeared in other Mac applications – iTunes 9 now sports similar drill-down menus to the iPhone's own iPod application, for example, while Core Location now helps Snow Leopard set your Time Zone on the Mac.

Apple owners will also have noticed that the glass trackpads on current MacBook Pros are also getting bigger and that they use multi-touch – a feature that first appeared on an Apple product with the iPhone.

iPhone menu

PHONE TO DESKTOP: Some user interface elements are shared between different OS platforms - iTunes 9 drill-down menus originally appeared on the iPhone

What's clear, though, is that Apple isn't going to suddenly junk 26 years of Mac OS X development in favour of an upstart OS like the one on the iPad. Susie Ochs, Senior Editor of MacLife says:

"Mac OS X is a lot more flexible, customisable. iPad OS is more walled off and basic since it's tied to one specific gadget."

One possibility is that Apple could go down the Microsoft route and bring full touch-screen capabilities to Mac laptops, or even to Mac desktops like the iMac. Ochs says:

"If people like using a touchscreen device and get really used to it, maybe Apple will put the touchscreens into some of its real capital-C computers too."

However Alykhan Jetha, CEO of developer MarketCircle disagrees. He told TechRadar:

"What they [Microsoft] have done [with Tablet PC] is take a desktop metaphor and shoe-horned into a tablet with a stylus and it doesn't work. It obviously doesn't work because it [Tablet PC] has not succeeded."

Snow leopard

THANK THE PHONE: The huge improvements in the performance and capabilities of QuickTime X on Mac OS X 10.6 Snow Leopard are down to Apple's experience with the iPhone

"The iPad is fundamentally different," Jetha continues. "It's even different from the iPhone. One of the things you immediately notice about the iPad is that the Unlock slide is in the middle of the screen. If it's in the middle of the screen you can't unlock it with one hand… The design cues are telling you that it's a two-handed device…"

"The interactive metaphor is very different on the tablet to the desktop. Will it [the iPad] replace the desktop in its current form? No."

-------------------------------------------------------------------------------------------------------

Liked this? Then check out Hands on: Apple iPad review

Sign up for TechRadar's free Weird Week in Tech newsletter
Get the oddest tech stories of the week, plus the most popular news and reviews delivered straight to your inbox. Sign up at http://www.techradar.com/register

Follow TechRadar on Twitter