Adobe plans to build a 64-bit version of its flagship image-editing software, Photoshop, but the upcoming CS3 version isn't the place to make that plan a reality.

"At some point it will make sense to do a 64-bit version. That wasn't this time around," said Photoshop co-architect Scott Byer in a blog posting last week, addressing feedback on the public Photoshop CS3 beta asking for a 64-bit version. Issues involving technology, performance and support mean that Photoshop will remain 32-bit software for the time being, Byer said.

On the technology side, 64-bit chips permit easier access to more than 4GB of memory (Windows only lets an application use a maximum of 2GB; Mac OS X will dole out up to 3GB). The 64-bit x86 chips have more internal memory slots called registers, which help a bit, but main memory access speeds aren't any faster on 64-bit chips.

When it comes to calculations, many 32-bit chips already can handle 64-bit math operations, he said. And 64-bit data structures, being twice as big as 32-bit ones, are therefore bigger consumers of memory bandwidth. "The number of situations in which an application being 64-bit is a performance win is very small," he said.

From a market perspective, 64-bit applications require 64-bit chips and operating systems, neither of which is a given. Mac OS X isn't fully 64-bit, meaning that zero customers can run 64-bit applications, and 64-bit Windows has penetrated to a "vanishingly small percentage" of customers. Windows Vista has better 64-bit support, but "the expected Vista adoption rates mean that the number of Photoshop customers running the 64-bit version of Vista will remain very tiny over the next couple of years."

Maintaining a separate 64-bit version of Photoshop would mean a huge opportunity cost in "features we can't do because we have to spend resources elsewhere" on quality assurance, testing another version of the application on multiple operating systems.

"Adding the cost of adding a 64-bit version to the mix of things that were already on the have-to-do list--especially in light of the very limited benefits--and doing a 64-bit version this cycle really became an unreasonable thing," Byer said.