[Editor's note: This article is part of our series of articles on installing and upgrading to Lion.]
For over a decade, installing the latest major version of Mac OS X meant buying a disc and slipping it into your Mac's optical drive. No longer. Mac OS X 10.7 — better known as Lion — is available for direct download. In fact, it's available only as a download from Apple's Mac App Store. In many ways, this new method of distribution is easier and more convenient. But it also raises a number of questions and presents significant upgrade obstacles for some users. Here's a look at the details of installing Apple's first-ever download-only OS.
Fair warning: If you install Lion now, keep in mind that you're installing the very first release. It could be fully baked and bug-free, but if previous debuts of major versions of Mac OS X are any indication, we'll see the first update, containing a number of bug fixes, within a few weeks. If your Mac is mission-critical — in other words, if downtime is not an option for you — you might consider holding off for the inevitable Mac OS X 10.7.1.
Finally, before proceeding, be sure to read my article on getting your Mac ready for Lion, which covers system requirements and recommendations, as well as a number of preparatory tasks that will help make the upgrade go smoothly. For example, you should update Snow Leopard to 10.6.8 and install the Migration Assistant Update for Mac OS X Snow Leopard.
Purchasing and downloading Lion
Assuming you meet the requirements, getting Lion is easy — with a few caveats, noted below. You simply launch the Mac App Store application, click the Lion banner on the store's main page (or search for Lion, or click this direct link), click the $29.99 button at the top of the screen, then click the Buy App button that appears. After providing your Apple ID and password, the Lion installer icon will be added to the Dock, and Lion will begin downloading. Specifically, the 3.8 GB installer application, called Install Mac OS X Lion.app, will be saved to your main Applications folder (/Applications). On my cable-model connection the morning of Lion's release, the download took approximately 39 minutes.
(Three quick notes here. First, if you purchased a Mac on or after June 6, 2011, but it didn't come with Lion pre-installed, you're entitled to a free copy of Lion. Visit this Apple web page for details. Second, if you're a developer who previously downloaded the "golden master" [GM] of the Lion installer, the Mac App Store will claim Lion is "Installed" on any Snow Leopard Mac — and thus not let you download the official release — if it detects that installer on any connected volume. The solution is either to delete the GM, after compressing it or copying it to a removable drive if you want to keep it handy, or to disconnect the drive on which the GM resides. Third, if you're trying download the Lion installer onto a Mac running the GM version of Lion, the Mac App Store will claim that a "newer version" is already installed and, again, prevent you from downloading it. The trick here is to Option+click the Buy App button in the Mac App Store. If that doesn't work, quit the Mac App Store app and then hold down the Option key while launching the Mac App Store again. One of these two procedures should let you download the release version of Lion.)
If you've got multiple Snow Leopard Macs, you can download the installer onto any of them — your purchase of Lion entitles you to install it on any of your authorized Macs. To download the Lion installer on one of these "secondary" Macs, you just launch the Mac App Store application on that Mac, click the Purchases button in the toolbar, and click the Install button next to OS X Lion in the list.
Alternatively, once you've downloaded the Lion installer onto one computer, you can copy it — over your local network or by using a flash drive, DVD, or external hard drive — from one Mac to another. You won't be prompted to authorize the installer on each Mac, as you are with other Mac App Store-distributed software — the Lion installer does not use digital-rights management (DRM), which makes it easy to use one installer to upgrade all the Snow Leopard Macs in your home.
However, there's a catch here: After downloading the Lion installer to your Mac, if you leave the installer in the Applications folder and use it to install Lion on your Mac's startup drive, the installer will disappear after installation — it's summarily deleted as part of the installation process, presumably to free up the nearly 4 GB of drive space it occupies. So if you plan to use that installer on other Macs, and you don't want to have to download it from the Mac App Store again, be sure to copy the installer to another drive — or at least move it out of the Applications folder — before you install.
Note that unlike all other software sold through the Mac App Store, subsequent updates to Lion will be provided via Software Update, not through the Mac App Store's update feature.