The feature, included in iTunes 10.5.1, can scan a user's library to find music and match the content to the music available in iTunes Store. If it finds a match, users don't need to upload the music and can listen to them anywhere, even better-quality versions, on any devices running Apple's iOS operating system. Music that doesn't match is automatically uploaded.

　　With a subscription fee of 24.99 U.S. dollars a year, users can store up to 25,000 of their own songs in Apple's cloud server. The iTunes Match is currently only available in the United States.

　　Subscriptions for iTunes Match are unavailable for a while Monday morning due to excessive demand.

　　The iTunes Match was first introduced in June along with Apple' s iCloud platform, the company's cloud service enabling users to sync their files, apps and content among Apple devices.

　　Unlike Google and Amazon, Apple got the official blessings from all four major music labels, making the company only need to keep one copy of each song in its cloud server, eliminating the uploading work for users and redundancies for servers.

　　When Apple's late co-founder Steve Jobs introduced the feature in his last keynote address in June, he touted the feature as "an industry leading effort," saying that the 24.99-dollar price is cheaper than Amazon's offering and Google has not announced a price yet.

　　The release is also ahead of Google's latest music push. In an email invitation sent out last Friday, the search giant said it will hold an event called "These Go To Eleven" on Wednesday in Los Angeles. Tech news website The Verge reported that it will be the debut of the company's cloud music service Google Music.