Apple CEO Steve Jobs will be on hand today to unveil the company's new iCloud service to compete with Amazon and Google.

Job look medical leave in January, and his appearance at Apple’s conference in San Francisco will be much analyzed by Apple’s followers.

Apple on April 31 announced it will unveil the iCloud service at Monday’s Apple Worldwide Developers Conference (WWDC). Jobs also is likely to unveil software updates for Apple’s iPhone, iPad and Mac.

Though Apple has been tight-lipped as to iCloud features, it’s expected that the service will allow syncing of email, contacts, files, photos and videos across multiple devices, in addition to Apple’s cloud music service.

The music service has been the source of much speculation, coming on the heels of similar offerings from Amazon and Google. The feather(s) in the cap for Apple -- despite iCloud’s late arrival to market -- are licensing agreements Apple has inked with three of the four top record companies.

The deals with EMI Music, Warner Music and Sony Music will allow consumers to stream music from the cloud to multiple devices without first uploading their music libraries. Bloomberg reports that the service will scan digital music collections and automatically mirror them in iCloud.

In contrast, users of Amazon and Google’s music lockers must first upload their collections -- a process that can take hours or days and must be repeated after adding new material (unless purchased through Amazon). Both companies decided to release their products without licensing deals with record companies.

The New York Times has a post comparing the Amazon and Google cloud services.

Meanwhile, “iSteve: The Book of Jobs," a biography by Walter Isaacson is not set to be released until March 2012. But it already seems like it will be a best-seller, based on presale orders on Amazon.com. Jobs has cooperated on Isaacson on the project.

The book was No. 13 on Amazon’s best-seller ranking Monday morning, and No. 1 in biographies and memoirs and No. 1 as well in science and technology books. The International Business Times reported the Amazon early sales.