Google Chrome OS is an open source, lightweight operating system that will initially be targeted at netbooks” and “most of the user experience takes place on the web.” That is, it’s “Google Chrome running within a new windowing system on top of a Linux kernel” with the web as the platform. It runs on x86 processors (like your standard Core 2 Duo) and ARM processors (like inside every mobile smartphone). Underneath lies security architecture that’s completely redesigned to be virus-resistant and easy to update.

Until today, Google’s Chrome OS has been little more than a wordy concept. Now, finally, we truly know what it is, what it looks like, and how it works. Here’s the breakdown:

Google went to great pains to emphasize that today’s event wasn’t a launch—that’ll come a year from now, apparently, with a public beta still well over the horizon. This is all about a seeing the OS for the first time; understanding in real terms how it’s different from what’s out there; figuring out why you might actually want to use it; etc. So! Here’s what we knew going in:

• It’s basically just a browser: meaning that it’ll be based around preexisting web services like Gmail, Google Docs, and so on. There are going to be no conventional applications, just web applications—nothing gets installed, updated, or whatever. Seriously.

• It only runs web apps: It’s going to integrate web apps into the operating system deeper than we’ve ever seen before, meaning that a) they’ll seem more like native apps than web apps and b) they’ll be able to tap into local resources more than a typical web app in Firefox, for example. They’re web apps in name, but they’ll have native powers.

• How, exactly?: With HTML 5. This is the next version of HTML, which gives the browser more access to local resources like location info, offline storage—the kinds of things you’d normally associate with native apps. More on that here.

• Chrome is Chrome: The user’s experience with Chrome OS will basically be synonymous with their experience on Chrome Browser. Technically speaking, Chrome OS is a Linux-based OS, but you won’t be installing Linux binaries like you might on Ubuntu or some other Linux distribution. Any “apps” you have will be used within the browser. Chrome OS is effectively a new version of Chrome, that you can’t leave. There are a few reasons Google’s pushing this, which we’ll get to in a bit.

• And as you’ve probably guessed, it’s super-light. It starts up in a matter of seconds, and boot straight into the browser. Likewise, the Chrome browser is apparently very, very optimized for Chrome OS, so it should be faster than we’ve ever seen it.

• It won’t support hard drives, just solid state storage. I mean, hard drives are dying, sure, but this is pretty bold. Hardware support sounds like it’ll be pretty slim, because:

• You’ll have to buy a Chrome OS device: You might be able to hack this thing onto your current machine, but you won’t just be able to install it to replace Windows, or opt for it on your next laptop, for example. You’ll have to buy hardware that Google approved, either component by component, or in a whole package. They’re already working on reference designs.

• For now, it’s for netbooks. It’s not intended for desktops, to the point that Google is saying that the first generation of Chrome hardware will be secondary machines.

Think of it this way: now, the buttons in your taskbar or dock are now tabs; your email client now runs within your browser, but stores stuff offline just like Mail or Outlook; your documents will still open with a few clicks, but they’ll be stored remotely (and locally only if you choose). It’s all the same stuff, given to you in a different way.