In a complete very surprising move, Adobe CS4 includes 64-bit support for the Windows XP and Vista platform, but not for Mac.

Mac OS X users probably won't get 64-bit support until CS5, the subsequent release of the graphics editing software, according to John Nack, Adobe's Photoshop product manager.

Iframes/JavaScript Tags: Nack attributes this unanticipated state of affairs to Apple's decision last year to halt development of 64-bit support for Carbon, a move which he says took Adobe and third-party developers by surprise. Adobe did make CS3 Intel-compatible, but kept Carbon as its core architecture.

In a recent blog entry Nack wrote, "At the WWDC show last June, [Adobe and] other developers learned that Apple had decided to stop their Carbon 64 efforts. This means that 64-bit Mac apps need to be written to use Cocoa [instead of] Carbon".

"We'll need to rewrite large parts of Photoshop and its plug-ins (potentially affecting over a million lines of code) to move it from Carbon to Cocoa."

According to Nack, 64-bit support in Photoshop offers the huge speed advantages for working with substantial images on systems with RAM of about 32GB and up. However, typical users could possibly see a performance increase of 8% to 12% when using the 64-bit version of Adobe's software compared to 32-bit.

That means Mac OS X users won't be able to take advantage of the performance gains in CS4, and those working with massive images will likely need to use Windows until CS5 is released further down the road.

A Note: Ironically, when Photoshop was initially released back in 1988, the software was available for Macintosh only. The product didn't even ship for Microsoft's platform until 1992, when Adobe ported Photoshop 2.0 to Windows.