As a counterpoint to the crushing disappointment that was Vista, which emerged with only a fraction of its promise intact, Apple’s OS X Leopard (10.5) is everything that Steve Jobs said it would become when Apple first placed that first unsteady cub in developers’ hands. Leopard is also a thick catalog of inventions and improvements that Steve flat neglected to mention, so thick that Apple had to resort to running the equivalent of a software project change log on its site for marketing purposes. You can’t possibly chew through that list. I’ve been testing and assembling my own list of relevant and remarkable changes in Leopard, a list that speaks to more professional and savvy Mac users as well as those who might switch (or are sure they’ll never switch) from Windows and Linux. I have to start the introduction to this series of hands-on Leopard stories with what I consider to be Leopard’s most impressive quality. For its 300 changes since Tiger (OS X 10.4), the line item reading of which provokes a range of reactions from the head nod to the ear-to-ear grin, there is not one ounce of fat, no feature in Leopard that you’d opt to leave on the DVD the next time you install it. Instead, for all that’s been added, Leopard remains trim enough to run on a PowerBook G4 with 512 MB of RAM. The very same OS is a robust, Open Group certified 64-bit UNIX when run on Intel Core 2 Duo and PowerPC G5 machines, with no need to buy a special edition. One of Apple’s marketing lines says that everyone gets the ultimate edition of Leopard because that’s the only edition there is. I’d argue that if Microsoft’s Vista product tagging is the basis for comparison, then all Leopard buyers get the 64-bit enterprise edition.Despite the fact that I’m far past this stage, the first hands-on experiences I can relate involve stability and installation. If you’re eyeing Leopard, one concern that you can cross off your list straight away is stability. I’ve spent several months working with Leopard as a developer and administrator. I began rolling Leopard into production on MacBook, MacBook Pro, Mac Pro and Xserve Xeon, against Apple’s advice but not requiring its consent, at a point well prior to its release. I’d be testing the bounds of non-disclosure to tell you when I felt Leopard hit its stride. Instead, I’ll just say that there is no need to obey the standard advice to wait for the first boatload of fixes before buying in. That’s true of Windows, and true of Linux, but not Leopard. Leopard shed its training wheels a while ago.Non-Mac users coming to Leopard will find a really simple, automated install experience, but it is more flexible than before. That’s most notable in network configuration, where auto-detection of wired and wireless networks is more accurate. It’s easier to enter the SSIDs of private Wi-Fi networks, and you can bypass network configuration entirely. OS X doesn’t phone home for authorization, so you can install completely and permanently without exchanging registration info with Apple.Existing Mac users thinking of taking the leap can safely take ease of upgrades and installation for granted, after they burn their most critical data to DVD or an external hard drive. Migration Assistant, which you can invoke at install time or at your whim later, transfers your user data and applications from Tiger to Leopard after what amounts to a clean install. The Leopard installer will let you do an overlay install, which updates the system software and tries to leave everything else alone. It is impossible to automate all possible cases, but I can’t imagine any user who could make Migration Assistant fail. Do be patient, though. Take measures to ensure that Migration Assistant runs uninterrupted, and understand that Migration Assistant’s estimated time to completion is a wild guess. In my experience, it finishes sooner than expected. As a taste of what’s to come, I’ll spend a few words on what I found to be the most substantial user interface enhancement: Spaces. Spaces gives you multiple virtual desktops, and you can switch among them via the keyboard, Dock or menu bar icon. It isn’t fast user switching–all desktops are the same user–but it’s more lightweight, and there’s no need to enter a password when you switch desktops. The unexpected killer here is that Spaces lets you target specific applications to selected desktops. So, for example, you can arrange things so that Mail always opens in Spaces’ second desktop, or you can set up separate developer and productivity desktops.I’ll go on from here through the weekend and into next week. I’m holed up in a hotel doing nothing but Leoparding. To tide you over until my next hands-on dispatch, you’ll find one Apple exec’s selected Leopard high points in this interview, and my thoughts on Leopard from a technologist’s perspective are in my Leopard: A Beautiful Upgrade column. Hang out. You’re welcome to the pull-out sofa, and you get used to the noise from the Xserve.Yes, there will be screens and video. Many, many visuals. Software Development