Adobe announced last week that only Windows users will be able to use the 64-bit version of PhotoShop CS4:
In a volte-face that will anger many Mac users, Adobe has announced that the Windows port of CS4 – the package containing such creative essentials as Photoshop and Illustrator – will be available in a 64-bit binary for users running compatible builds of Windows. The Mac version, by contrast, will only be available as a 32-bit executable until the next release, CS5.
The 64 bit support enables users to work on massive images easily, with the biggest speed gain seen on Windows systems running 32GB or more of RAM. For us mere mortals struggling long with quantities of RAM that don't require a second mortgage, the speed increase will still be a not inconsiderable 8-12 percent over the 32-bit build.
The reason for Adobe to seemingly snub its core market of Mac users is, ironically, all Apple's fault. Last June, Apple announced that they would not be providing a 64-bit version of their Carbon procedural API. Any applications based on Carbon that would like to enter the 21st century with 64-bit support will need to be re-written for Cocoa which can produce both 32 and 64 bit code. Adobe was just one of the companies taken by surprise when Carbon all but bit the dust.