Android is a Linux-based open source operating system for handheld mobile devices such as smartphones and tablets. At the time of writing, it powers about 75% of the world's mobile devices. The remaining market shares are taken by Apple's iOS (approximately 18%) with various other, more obscure platforms (Blackberry, Windows Phone, Symbian, etc.) taking up the remainder.
Android was initially produced by a company called Android, Inc., in 2003. The company was purchased in 2005 by Google and the first non-beta version of the OS, Android 1.0, debuted for the HTC Dream smartphone in September 2008. New versions followed fairly regularly, and with the release of 1.1 in February 2009, all Android releases since have carried cutesy pastry-, candy- or dessert-based nicknames.
Below is the junk food-based version roundup. I've lumped some of the point releases together, so the date on some of these reflects only the date of the initial releases.
|Android version||Code name||Release date||Linux kernel
|Pre-1.0 beta||None||November 5, 2007||2.6.22
|1.0||None||September 23, 2008||2.6.23
|1.1||Petit Fours||February 9, 2009||2.6.27
|1.5||Cupcake||April 30, 2009||2.6.27
|1.6||Donut||September 15, 2009||2.6.29
|2.0 - 2.0.1||Eclair||October 26, 2009||2.6.29
|2.2.x||Froyo||May 20, 2010||2.6.32
|2.3 - 2.3.7||Gingerbread||December 6, 2010||2.6.35
|3.0 - 3.2||Honeycomb||February 22, 2011||2.6.36
|4.0 - 4.0.4||Ice Cream Sandwich||October 19, 2011||2.6.39
|4.1 - 4.3.1||Jelly Bean||June 27, 2012||3.0.31
|4.4 - 4.4.2||KitKat||October 31, 2013||3.8
|5.0 - 5.1.1||Lollipop||June 25, 2014||3.9
|6.0 - 6.0.1||Marshmallow||March 9, 2015||3.10
Because Android is made by Google, you'll need a Google account to use an Android phone. My Google account, which was created in 2004 when I got a Gmail account, then rolled into the Google account architecture some years later, is what I used to set up my Android phone and access the Google Play Store. A Google account is also necessary for using services like Google Wallet, Google Drive, Google+, Google Talk and even Google search settings. Additionally, your phone contacts and browser bookmarks are automatically synced to the Google Cloud from your phone.
Heavily-modified custom versions of the various Android releases are widely distributed around the 'net. They are known as ROMs. A number of technical hoops must be jumped through with the device's configuration to install them and ensure that they work. Some of the more popular ROMs include ClockWorkMOD and CyanogenMod. No, I'm not sure why they're referred to as "ROMs", when "ROM" means "read-only memory" and "ROM" in this case represents a modified (decidedly not read-only) build of Android.
You might think that Android's Linux internals would frighten off a great many consumers, but this is evidently not the case, given how popular Android devices are. Average consumers probably aren't aware and/or don't care that it's based on Linux, and an even larger group of such people probably aren't aware of what Linux even is. But this is all fine and good. Android devices are, as a rule, much less expensive than Apple's iPhone/iPad/iPod family of devices, and they lack the debateably "professional" reputation that many people consider Apple devices to possess. So, where as Linux on the desktop or laptop computer would probably put off people with middling or zero technical knowledge, they don't mind it at all on their phones and tablets, if they're actually aware of its presence there.
Rightly so, in my opinion. Gingerbread, released mostly on devices manufactured in 2010 and 2011, and presently the most common version, is a joy to use. The interface is fairly intuitive, smoothly animated and very stable. Crashes (which, on a smartphone, manifest as spontaneous reboots) are very rare. Mobile operating systems are supposed to be simple, after all, to save time, and Gingerbread accomplishes this with aplomb. Those users with Ice Cream Sandwich and Jelly Bean usually are running those versions on older phones that they upgraded themselves or on brand-spankin' new devices that they purchased specifically so they could use those versions. And despite Android drawing those put off by Apple's businesslike nature, Android itself has a very similar nature, though it's much less noticeable. Being open source, anyone can develop applications for Android, and as of this writing, the Google Play app store has about 700,000 apps—roughly the same amount of apps that have been developed for Apple's iOS. This may seem a little lopsided given Android's much higher market share, but that can be explained by the likelihood of Apple users having more technical aptitude per Apple device sold, whereas the average baby boomer or soccer mom who wants an inexpensive phone will certainly never develop an app for it (barring exceptional cases, of course).
Android and Apple devices can be used on more or less the same number of mobile service carriers in most countries. The biggest factor in Android's dominance, it seems, is cost. Android devices are much less expensive than Apple devices and thus more palatable to consumers. One could easily buy two or three mid-range Android phones (the HTC Evo, for instance, or the Samsung Galaxy Reverb) for the price of a current iPhone 5 64GB.
Being based on Linux, Android has both normal user accounts and superuser accounts. New devices ship without the superuser account enabled, but anyone with a few minutes' time on their hands can enable the superuser account through a process known as rooting, which is identical in purpose to jailbreaking an iPhone. I suspect that the phone makers don't enable root by default on any devices to protect average users from themselves—the same principle employed in most computing environments. My phone, an LG Optimus Elite, was rooted by a simple script I found in an Android users' forum. I rooted my girlfriend's phone (an LG Optimus Slider) through a slightly different but similar method. Rooting an Android device gives its user a much greater degree of control over the way the device operates. Average users would have no use or desire for advanced customization, which is fine with me and with the developers of Android. No fuss.
As for features, devices equipped with an ARM7 or newer processor (read: released in 2011 and later) can utilize Adobe Flash and HTML5 video. Java is in a state of constant flux and it's a toss-up as to whether or not it'll be on any given version of Android due to an apparently sticky legal battle between Oracle (the makers of Java) and Google (hat-tip to motiz88 for this information). SQLite is used for all database purposes. Bluetooth and touchscreen functionality are standard (as they are on every modern smartphone). Some devices support tethering, but official support is spotty. Voice input is supported on all versions but I don't know a single person who uses it because it can't understand what it hears half the time; though I've heard in newer versions, voice input functionality and ability to distinguish words has improved some since earlier versions. All the standard web browsers other than Microsoft Internet Explorer (Chrome, Firefox, Opera) and a few mobile-only outliers (Dolphin, UCB) are available, though not all of them work on all versions of Android. Most devices are capable of supporting HD video and streaming media. Google Wallet is standard on versions 2.3.7 (Gingerbread) and up. Most Android phones are able to use microSD cards of any capacity for additional disk space. The only ones that don't have an SD slot are generally the models that come with 8-64 GB of internal storage space, such as the Samsung Galaxy line. Generally, Android tablets don't include SD slots.
Google is remarkably open about Android development, as expected for an open source product. They've produced a software developer's kit for aspiring and experienced developers. Android user forums are legion and, more often than not, contain the answer to whatever issue you're dealing with or question you may have. As with Linux, the community is by and large made up of hobbyists working for free. Some of the apps available are not free, but most don't cost more than a few dollars and are more feature-laden than the free or "lite" versions of those apps that are available. (e.g., ROM Toolbox Pro vs. ROM Toolbox Lite). Both are toolkits for rooted phones; the "Pro" version offers more features.)
Android-licensed devices are available from the following companies:
Also available are Android-licensed smart watches, which run stripped-down and fast versions of Android. Popular makers are Huawei, Aipker, Samsung, Asus, and many other brands. Most include a bodily vitals meter that counts your steps and so forth. I can't wait until these are available as wrist implants!
Samsung has become the large gorilla, or 600-pound kitten (if you prefer), in the room due to their court battles with Apple over the similarity of their phones and tablets, particularly the Samsung Galaxy family, to Apple's iPhone and iPad.
Various versions of Android can be installed on devices for which it was not intended—through various degrees of hacking—such as HP's Palm products and the late, lamented HP TouchPad, which was announced with great fanfare in early 2011 and was dead and buried by early 2012. The Blackberry 10 can run Android apps, too, but nobody really cares because it seems like only corporate types use Blackberry devices. Barnes & Noble's Nook e-reader tablet runs outdated versions of Android (1.5 to 2.3) but remains a popular alternative to the Amazon Kindle e-reader, which also runs a Linux-based operating system (not Android).
All told, Android is a great operating system. Of course it is—it's Linux! I'm sure everybody reading this already has a smartphone or modern tablet and doesn't need me to tell them what to use or change their preference. But I thought it'd be nice to node this in the interest of completeness.
Update: I switched to an iPhone 5c, running iOS 7.0.4, in November 2013. The jury is still out on which is more fun to use—Android or iOS—but I will say that iOS is much faster and its GPS capabilities much more precise.
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Not to be confused with Android Lust, Marvin the Paranoid Android or Lieutenant Commander Data.