Mac Or PC

[MikeA]

Actually, neither Unix, Mac or Windows are anything like Real Time OS's. There are kernel options for linux and a few realtime Linux distributions though. Not really something you would want to run your desktop on though... Real-time operating system - Wikipedia, the free encyclopedia

I know what you mean though, Noel. You're talking about desktop responsiveness. There used to be a huge and very noticeable gap between Mac and PC, but I have to say the switch to intel and OSX has just about blown that away. Probably the improved mhz helped things along too. My opinion is that Apple held onto the mhz myth marketing for way too long, and delivered systems with compromised memory and IO bandwidth at the lower end of the range to drive sales at the top end.

I certainly never notice it like I used to (I'm switching between OS's all the time)

Mike.

[ThomasSapiano]

Just stumbled on this thread and figured that I'd try and help clarify things a bit with respect to 32-bit memory usage on a 64-bit OS X platform.

Originally Posted by Jerry Skrocki

I have 12 gigs of ram on my Mac Pro running Leopard and I know Photoshop CS3 is using ram above 3072 mb for filters and scratch data before writing to the hard drive.

0 Page outs

That's not really a direct indicator. The limits on 32-bit software are imposed on the virtual memory space that it can use, so as long as there is sufficient physical memory available all of that data can remain resident and page faults won't occur. That is, 32-bit software running on OS X can only work with 4GB of data, regardless of whether that data is in physical memory or the pagefile. To work with larger data sets, software must take its own measures.

Photoshop works around this problem by using its own memory management subsystem that manually moves data between it's virtual memory space and the scratch disk. This happens independently of the operating system, and will not be logged as a page fault (as far as the OS is concerned it is no different than saving a file). This implementation has allowed Photoshop to work around the limits of 32-bit architectures for a while now, however it is also why it is so hard to port it to 64-bit platforms (as it requires a complete overhaul of a central component of the program that is touched by nearly everything else).


OS X can potentially cache the read/write operations that Photoshop is doing wrt it's scratch disk, however this isn't the same thing as natively accessing the memory. When this data is cached, the pages still have to be shuffled between Photoshop's memory space and the cache - eating up time and memory bandwidth. It is certainly much better than accessing that data on a hard-drive backed scratch file, but the performance still takes a significant hit when compared to native access.

That is, 32-bit versions of Photoshop will indeed benefit from having more than 4GB of memory in a 64-bit machine, but not nearly as much as a native 64-bit implementation. Using caching tricks can help to mitigate the performance loss seen when data needs to be moved to/from the scratch disk, but it doesn't come close to eliminating it.

Unfortunately, Adobe's documentation isn't very detailed on exactly how they manage memory within this context. Their support notes provide some vague descriptions, but provide little detail and in practice are often somewhat optimistic. It also isn't clear why Photoshop's memory allocation slider only allows you to select a maximum of 3GB of RAM, as OS X doesn't split the virtual address space into user and kernel spaces like Windows (and most other OSes). Keeping things vague is certainly understandable as they don't want to divulge their trade secrets to potential competitors, but it makes it difficult for users to objectively assess the performance ramifications of certain equipment choices.


With all of that said, some plug-ins operate in separate processes from Photoshop itself, providing them with their own virtual memory space. Plug-ins designed in this way will therefore be able to use up to 4GB of memory for their own purposes, and (more importantly) won't take away from the memory space that Photoshop has access to. As such, if one is using a lot of these plug-ins then adding the extra memory can provide dramatic performance benefits.

[Jerry Skrocki]

Resurrecting this thread now that Photoshop CS4 has been released has some merit. Adobe has revised their Photoshop Optimization Tech notes to reflect the changes.

For OSX:

View Document

"Photoshop can directly access 3.5 GB of RAM when run on Mac OS (10.4.11 or later). If you have additional RAM on your computer, the RAM above 4 GB is used by the operating system as a cache for the Photoshop scratch disk data. Data that previously was written directly to the hard disk by Photoshop is now cached in this high RAM before being written to the hard disk by the operating system. If you are working with files large enough to take advantage of these extra 2 GB of RAM, the RAM cache can increase performance of Photoshop.

When you run Photoshop CS4 on a 64-bit operating system Photoshop can access up to 8 GB of RAM. You can see the actual amount of RAM Photoshop can use in the Let Photoshop Use number when you set the Let Photoshop Use slider in the Performance preference to 100%. The RAM above the 100% used by Photoshop, which is from approximately 3 GB to 3.7 GB, can be used directly by Photoshop plug-ins (some plug-ins need large chunks of contiguous RAM), filters, and actions. If you have more than 4 GB (to 8 GB), the RAM above 4 GB is used by the operating system as a cache for the Photoshop scratch disk data. Data that previously was written directly to the hard disk by Photoshop is now cached in this high RAM before being written to the hard disk by the operating system. If you are working with files large enough to take advantage of that extra RAM, the RAM cache can increase performance of Photoshop."

For Vista 64:

View Document

"Although the 64-bit version of Photoshop will speed up some operations, it won't speed all of them, nor will it speed the operation equally. Generally, operations will run approximately 8-12% faster. Overall, processor speed is not the main advantage of using the 64-bit version.

The primary advantage of using the 64-bit version is to access amounts of RAM beyond what Photoshop can access when the 32-bit version is run. You can take advantage of more than 4 GB of RAM only when you are on 64-bit Windows, using 64-bit Photoshop. If you use files large enough to need more than 4 GB of RAM, and you have enough RAM, all the processing you perform on your large images can be done in RAM, instead of swapping out to the hard disk."

[Noel_Carboni]

Some anecdotal information:

I have Vista 64 and CS4 on a 3 year old Dell Precision workstation with 8 GB of RAM.

I processed a medium sized astroimage the other day... This involved literally hours of work on a 6 megapixel image - thousands of steps, and a number of actions invocations, each of which runs dozens of steps or more.

I loaded up a color image using CS4 32 bit, as I use the FITS Liberator plugin to import images from standard format FITS files. Then I saved the image as a .psd file, closed CS4 32 and switched to CS4 64.

You should know I always set my number of History states to the max: 99. I just like it that way. This does put a bigger strain on RAM usage.

Anyway, I worked for quite a while in CS4 64, and only once noticed any kind of delay in the responsiveness of the user interface. Just once, after many hundreds of steps, Photoshop went silent. Seeing the hard drive light on, I just left it alone for a while, and sure enough responsiveness returned.

I do save my work from time to time, but it's always disconcerting to have the application become unresponsive. Adobe really earned some points with me when it came back.

I've never had CS3 go that long and remain responsive. Usually it goes away for a while from time to time while swapping things to the hard drive.

Toward the end of the editing of this particular astroimage, I pasted it into a big mosaic I have under construction (basically, we shoot small parts of the sky and stitch them together into wide field high resolution images). Again, working with a relatively large multilayer file in 16 bit per channel mode was far better in Photoshop CS4 64 bit than it has been in CS3. It just kept on working, where I really have come to expect some swapping activity.

The GPU enhancements plus the extended responsiveness the larger memory space is providing have made me a happy camper.

-Noel

[Martin_Doudoroff]

Originally Posted by Noel_Carboni

The GPU enhancements plus the extended responsiveness the larger memory space is providing have made me a happy camper.

Now that you've been using CS4 for a while, what are those GPU enhancements doing for you? Is it principally an aesthetic refinement (pleasure), or does it really impact your process and/or results?

[Noel_Carboni]

To be brutally honest, all they really do is polish the user interface some, making the editing process a touch more fun. Virtually the only place I see the GPU at work in the smooth zoom in/out (and only then when I don't have "Resize Windows to Fit" checked). I don't use the "hand" tool to grab and drag my canvas (preferring instead to use the Navigator palette when I'm zoomed-in).

Having just upgraded to Vista/Aero, and with a new video card, in general I am getting a more refined user interface overall, so the "gee whiz, this feels new" factor applies. Frankly and in all seriousness, I could live without the GPU enhancements in Photoshop.

This is a bit OT for a "Mac vs. PC" thread, but to add to my comment above, I wish Adobe had implemented a "Switch to 64/32 bit" menu (e.g., like the old "Edit in ImageReady" from years gone by). I find myself having to switch to 32 bit PS to run a few plugins, which thankfully are generally near the beginning and end of my editing regimen.

-Noel

[Martin_Doudoroff]

Noel: thanks for the assessment. I haven’t decided whether to shell out for CS4, although it may be inevitable. (At the moment, it looks like I would actually benefit most from the changes to Illustrator.)

In a semi-related note, Lloyd Chambers has posted about a couple of irritating discoveries on the Mac side of Photoshop CS4.

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