by , 1:40 PM EDT, June 11th, 2007

The 32-bit operating systems Mac users have been accustomed to are about to become a thing of the past: Mac OS X 10.5 will be 64-bit from top to bottom. Apple CEO Steve Jobs made the announcement during his World Wide Developers Conference keynote presentation on Monday morning.

Unlike other operating systems that come in different 32-bit and 64-bit versions, and require applications to be compiled for each version, Leopard will run both application types at the same time. According to Mr. Jobs, this is the first time that 64-bit operating systems are "going mainstream."

The 64-bit version of Leopard that Mr. Jobs demonstrated offered substantial performance improvements over 32-bit versions of Mac OS X, and was able to open larger files and store more information in memory - one of the benefits of a 64-bit operating system.

Although Mr. Job's has not yet confirmed that Apple will transition from the HFS+ file system used today to Sun's ZFS file system once Leopard ships, a 64-bit operating system would go a long way towards helping Apple take advantage of the larger file sizes that ZFS supports.

Presumably Leopard will be coded so that it also runs on 32-bit processors as well.

Mr. Jobs also demonstrated other new Leopard features including a redesigned Desktop with Stacks, a revamped Dock, Quick Look, Spaces, and Time Machine.

Stacks allow users to group items together, like documents or applications, and access them through a single icon in the Dock. Items spring up out of Stacks from Leopard's new 3D Dock for quick access.

Leopard's Stacks feature and new 3D Dock.

Spaces and Time Machine were both demonstrated last year at the 2006 World Wide Developers Conference. Spaces allows users to create virtual Desktops without the need for additional monitors. Instead, users switch between virtual Desktops, or Spaces, that contain the windows and applications they want.

Time Machine is an automatic data backup application that keeps track of files so users can "go back in time" and recover any version of a document. It works transparently, so users don't have to take the time to manually create their backups.

Quick Look lets users see a preview of their documents without actually opening them. It also looks inside documents, so users can preview the contents of multi-page documents like PDF and Keynote presentation files. Developers can create their own preview plug-ins, so their applications and documents can take advantage of Quick Look, too.

Preview multi-page documents with Quick Look.

Mr. Jobs also mentioned that there were "over 300 new features" in Mac OS X 10.5, but he only showed off a small handful, and some of those features were repeats from last year's WWDC. That means Apple still has a few surprises left in store for Leopard's scheduled October release.

[This article has been updated with additional information about Mac OS X 10.5.]