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Dec 22, 2006

Is Photoshop CS3 a 64 bit app?

Another contentious topic to be found on the Photoshop CS3 forum is the question of whether or not Photoshop CS3 will be a real 64 bit application or remain a 32 bit application as it has been for a good long while. The hardware and OS vendors have done a good job of hyping 64 bit OS as the next big new thing, but unfortuately, the hype always precedes the reality.

To counter the cries for a full 64 bit rewrite of Photoshop, Scott Byer (Photoshop co-architect) has posted a story on his Living Photoshop blog entitled 64 bits…when?

Scott says:

I’ve gotten a number of questions on the beta forums as to why Photoshop CS3 won’t have a 64-bit version. It’s definitely a when question, not an if, and there are a lot of factors involved. I though I might collect some of the information together here.

First, let’s check all the 64-bit hype at the door. Being a 64-bit program means, most simply, that pointers in an application are 64 bits wide, not 32 bits. A 32 bit pointer means that an application can address 2 ^ 32 bytes of memory, or 4GB, at the most. The operating system an application runs on slices that application address space up, so that the application can actually only allocate a part of that address space for itself.

Thus, on Windows XP, an application can use 2GB of address space, on Macintosh OS X 10.4, an application gets 3GB, on Windows XP 64-bit edition, a 32-bit application gets nearly 4GB of address space. Applications don’t allocate RAM on most modern operating systems – that’s a common misconception and a gross oversimplification your computer geek friends tell you because they don’t want to explain virtual memory, TLBs and the like.

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