Last week, Apple took most Mac users by surprise when it released a developers preview of Mountain Lion, the company's newest desktop operating system, and announced it would ship the upgrade this summer.OS X Mountain Lion, the first in a yearly upgrade schedule, sports new features, many of them borrowed from the iPhone and iPad; a new security framework that should stymie the most common kinds of Mac malware; and tighter ties to the company's iCloud sync and storage service.But because Apple's not yet disclosed all the facts about Mountain Lion, you probably have questions.We've tried to fill in the blanks.When can I get Mountain Lion? Apple's only given the vague "late summer" due date, summer being relative, since in four months the southern hemisphere will enter winter. August 2012 is our bet: That syncs with Snow Leopard's Aug. 28, 2009, release.Even that, though, is a guess, since Apple's on new ground here. It usually unveils an OS a year or more before it ships, then pins a release month at its June developer conference. In 2009, for instance, it told users to expect Snow Leopard in September, but beat that by a few days. Last year, it pegged Lion's release to July, which it met with 11 days to spare.What about the preview? Can I get that now? Only if you're a registered Apple Mac developer . Membership in the program costs $99 per year.How much will Mountain Lion cost? Apple hasn't said, but if it's not $29.99 or less we'll eat our hats. That was the price of Lion last year -- and 2009's Snow Leopard was $29 . And while Apple hasn't officially committed to under-$30 for all upgrades, Mountain Lion is, like Snow Leopard, an incremental update, rather than the more ambitious Lion.That's why we would be surprised if Apple charged more for Mountain Lion than it did for Lion.How is Apple distributing Mountain Lion? Like Lion, through the Mac App Store.Although Apple offered Lion on a flash drive last year to quell concerns from some that they didn't have the bandwidth to download the multi-gigabyte upgrade, according to Pocketlint , the company won't repeat the USB offer with Mountain Lion.Can I upgrade to Mountain Lion? We don't know. The developer preview requires Lion or Snow Leopard, and although it makes sense -- together those two editions powered 80% of all Macs that went online in January -- that could change by the time the final code is ready.Apple has also told developers which Macs will run Mountain Lion's preview . The list excludes such notable systems as the now-discontinued white MacBook, the first-generation MacBook Air and all iMacs prior to the August 2007 20- and 24-in. models.With some exceptions, Macs sold from 2008 forward will run Mountain Lion, while 2009 and later models are guaranteed to run the new OS.As with other system requirements, the out-in-the-cold list could change by the time Apple ships OS X Mountain Lion.How many machines do I get to put Mountain Lion on for my $30? Since the upgrade will be delivered through the Mac App Store, the market's guidelines apply: All your personally-owned Macs can be upgraded for the one price.How can I get a free copy of Mountain Lion? Buy a new Mac this summer. Apple will probably repeat previous offers that have awarded buyers of new Macs a free copy of the new operating system.Last year, Apple gave away Lion to customers who bought a Mac between June 6 -- the date the company officially unveiled Mac OS X 10.7 -- and Lion's eventual Aug. 28 release date. Later, it extended the offer to cover all Macs that were sold equipped with Snow Leopard, no matter the sales date.Apple will likely run a similar "Up-to-Date" deal this year with Mountain Lion.I'm responsible for several dozen Macs in our business.... How do I upgrade them? Not sure, but going by Apple's past practice, you'll probably buy upgrade licenses in bulk then use a single redemption code to download an installer from the Mac App Store that you deploy and run on each machine.Will I be able to run any Mac application on Mountain Lion? I've heard Apple's blocking some apps. You're talking about Gatekeeper, the new security model that will by default let you install only software downloaded from the Mac App Store or programs created by authorized developers.Gatekeeper is Apple's reaction to last year's spread of the Mac Defender malware, which was tucked into fake security software: Gatekeeper will prevent such "scareware" from ending up on your Mac.But Apple isn't locking Macs to the Mac App Store, as it does with iPhone and iPads, which -- unless they're hacked, or "jailbroken" -- can run only apps obtained from the App Store. A quick change of Gatekeeper's default preference lets you install software acquired from any source.Why should I upgrade? Always an excellent question, even when the price is right. Apple has touted several new features, but the overriding theme is that Mountain Lion continues the practice the company debuted when it borrowed a few things from iOS for last year's Lion.That means Mountain Lion might be most compelling to users who also own an iPhone or iPad, and want a more consistent look and feel between their Macs and mobile devices. The new OS X applications and services -- ranging from Notification Center and Notes to Game Center and Reminders -- that Apple has touted originated on the mobile side, and other, already-on-the-Mac applications have been renamed to match the labels on iOS.From what we've seen, there are few user interface changes in Mountain Lion, so if you're looking for a visual revamp, you may want to pass.What new integration with iCloud does Mountain Lion sport? Mountain Lion adds a "Documents in the Cloud" view to the Open and Save dialog boxes of Mac applications that support the feature: Apple's home-grown apps, such as TextEdit in OS X and the for-a-fee Pages, Numbers and Keynote components of iWork, do. Most third-party software, notably Microsoft Office, does not.You can also create folders the iOS way by dragging and dropping one document atop another.Documents saved to iCloud -- or moved there from a Mac's hard drive by dragging from the Finder -- are automatically available on all iCloud-synced devices, including iPhones, iPads and Macs.It's unlikely that Microsoft will modify Office to let customers save and open documents to and from iCloud, since Apple allows only software sold through the Mac App Store to access iCloud storage. While Microsoft has never explained why it doesn't sell Office in the Apple e-market, the 30% cut that Apple takes of all revenue is probably top of the list.Another reason: Microsoft pitches its own online storage service, SkyDrive , as the way for Office users to share and synchronize documents.Any other notable new things in Mountain Lion? Likely lots that Apple hasn't yet described, but our favorite known change is the disappearance of a separate Software Update mechanism. Starting with Mountain Lion, Apple is using the Mac App Store to deliver OS updates composed of security patches and other bug fixes. In the preview, selecting "Software Update" from the Apple menu launches the Mac App Store, which then checks for available updates.When will we learn more about Mountain Lion? We're betting at this year's Worldwide Developers Conference (WWDC), which historically has been a wellspring of information about any impending OS.Apple has yet to set the 2012 dates for WWDC, but according to the calendar of San Francisco's Moscone Center -- the venue Apple has used since 2003 -- the week of June 11-15 is tagged with the generic "Company Meeting."The Moscone Center has used the same placeholder the last two years to mark the schedule eventually confirmed for WWDC.(The same week this year as the last two WWDCs, June 4-8, is partially booked by the Design Automation Conference, a get-together for electronic automation and embedded systems engineers and designers.)Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer , on Google+ or subscribe to Gregg's RSS feed . 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