Apple founder Steve Jobs emerged briefly from medical leave on Monday to announce the company’s latest venture—a music and video storage and delivery service that signals a dramatic shift in the technology industry and promises to upend the way users access information.

Called iCloud, the Apple service will allow users to request a spot on the company’s servers to park their iTunes library and beam whatever is there to any device. The service will be free.

Speaking at the Worldwide Developer’s Conference in San Francisco, Jobs said that because of the proliferation of consumer tech gadgets, the system of storing music and video on one central device has “broken down.”

“Keeping these devices in sync is driving us crazy,” he said as the audience applauded. “We’re going to demote the PC and Mac.... We’re going to move the digital hub, the center of your digital life, into the cloud.”

While music and video are expected to be the big draw for iCloud, the service will also be able to store other data, such as documents and photos.

But iCloud is more than just a “hard drive in the sky,” Jobs said.

The information obtained or uploaded to one device will automatically sync with other devices. Users that take pictures with their iPhones, for example, will instantly be able to access the photos on their iPads.

The announcement was a victory speech of sorts for Jobs who for more than a decade has been talking about a future where music, videos, books and pictures could be stored somewhere on the Internet—“the cloud”—and sent to a portable device anywhere there’s a cell phone tower or a Wi-Fi connection. That world, as Jobs envisioned it, would be free of the PC, the platform his nemesis Bill Gates built his fortune on and that Apple’s Macs could never quite compete with.

Apple is hardly the first to launch such a service.

In late March, Amazon launched its Cloud Player, a music locker that stores online streaming music. Google followed suit weeks later with the beta launch of its Music program, which lets users upload their music libraries, playlists and play count lists into its service and sync it across the Web.

But while Apple is the last of the major tech companies to enter the market, it has several advantages over the others. First, it has managed to seal deals with several record labels to sell their music, according to news reports, eliminating the need for customers to to upload music to a cloud locker. Second, it’s free. Before the announcement, analysts had speculated that Apple would price the service at a very low $25 a year.

Outside the realm of entertainment, businesses have been accelerating their move into the cloud in an effort to save the millions of dollars they must pay for servers and services associated with maintaining their own networks. The federal government is also adopting cloud computing.

Jobs said Monday that iCloud would also incorporate elements of a full office suite, putting it into direct competition with Microsoft’s dominant Office Suite and Google’s suite of basic office Web applications.

But storing information on the cloud comes with certain risks.

A General Accounting Office report released last year points out that federal agencies could lose control over their data or that information might be unprotected or even deleted by cloud providers.

Apple’s previous attempt at launching a Web service, MobileMe , a cloud-based document, calendar and contacts service, has been criticized for frequent bugs and snags, as well as its high $99 annual price tag.

Apple executives also announced updates to the company’s mobile and computer operating systems.

Apple’s next mobile operating system, iOS 5, is focused on mobile, with deep integration with Twitter and other social networks. Users only have to sign in once to use Twitter on an iOS device, and they can Tweet from Safari, YouTube and Maps with contact integration. The new system also lets users send messages to other Apple iOS devices, directly taking on Research In Motion’s BlackBerry Messenger.

OS X Lion, the latest installment of the operating system, emulates the mobile platform with a heavy concentration on apps and the Mac App Store. Apple slashed the price of its operating system — traditionally $129 — to $29.99. In another departure from the status quo, the company is also only offering the system over its Mac App Store.