[NordicMan]

I am curious about Photoshop and multiple cpus. Since the 9500 MP, Photoshop has been able to use them, however, it is much more optimised for the Mac processors now.

So, if two cpus are good, Photoshop must be able to make use of more.

I am thinking this, as one photographer I met told me that he was wanting to build a 4 cpu Athlon to use Photoshop. He is a pc guy, seems in that mold, and to quote him, "Photoshop will make use of whatever you throw at it." I asked him about using a Mac, he acknowledges the virtues, however, figures he will have to retool his thinking for that.

[larkost]

This gets into where you really have to understand how computers work... at the lower levels...

Most of Photoshop is a single threaded application, so it only sees a benefit from multi-processing because other tasks will move away from the processor that it is running on. The multi-threading needed to allow for real use of multiple processors is a lot of work, and adds a lot of complexity. Take that and add it to the very complex nature of the backbone of an application like Photoshop that has to run as the main application of an artist's workflow... and do so with as few changes across two radically different OS's running on two very different processors with different compilers, and you have a nightmare to make. So Adobe did the sensible (and right) thing, and made the backbone single threaded.

Now... before people get too bent out of shape... Much/most of the heavy lifting in Photoshop happens in the filters, and here is where Adobe has spent a lot of time allowing for things to be multithreaded, and here is where it really pays off. When you start applying filters, and a lot of the rendering (for example rotating an object) Photoshop can use as many processors as you can throw at it.

And the filter section is also where the the vector-processor (like) SIMD (single instruction multiple data) tricks up the processors sleeve can also come into play. Intel has MMX/SSE/SSE2, the Motorola design is called Altivec (Apple calls it Velocity =Engine... and IBM has a variant that is instruction compatible), and AMD has something similar to Intel's version. In many cases how efficiently these instructions are used can be much more important than how many processors you use.

Altivec is the the king of this group, and can process 4 32bit operations at the same time, or 8 16bit ones... and that is per unit, there are multiple per chip. When you add that with the complexity of co-ordinating multiple processors (expensive in resources on the motherboard), and trying to shuffle data all over the place, the SIMD usage can be the most important thing in performance.


Now, a couple of historical notes:

The older Mac "multiprocessors" like the 9500MP and the Daystar MP were not full "symmetric multiprocessors" like the current crop, they had one main processor , and the n multiple "co-processors", for doing things like Photoshop processing this design can have a slight edge in performance, but it does nothing for the general case, or whe running multiple programs.

The other point is that for most artists, switching to the Mac will actually make life easier (after a period of adjustment), as the MacOS tends to disappear into the background, and let your work up front. Plus, for most artists it is easier to find people who can help out with the questions they will run into on the Mac than the PC. And in terms of color syncing... you just can't depend on the results from a PC... People spent a lot of money trying to make it work on NT... but where are those companies now?

[NordicMan]

Ah, there is the kind of answer that I have been looking for. It is the kind of thing that I am curious about. I knew that Photoshop had made some accomodation for the multiple cpu Macs, 9500, 9600, even some 8600s, and for the Daystar.

Thanks for the information.

Yes, your last note is what I had shared with the fellow. It is like John Warnock said one time in an interview about colour and its science. "microsoft just doesn't get it." He was talking about his history, PostScript, the platforms, and the history of computing, and its future.

Now how do these instruction sets work, they are in the processors? I do not comprehend that. One reads about the simd, the Altivec, and the AMD set, that they have these.

[larkost]

Arstechnica has a series of good in-depth articales about SIMD, such as this one.