Photoshop CS5 Maximum Memory on Mac Pro, MacBook Pro, iMac
Actual memory available to Photoshop is always less than that, because the system scarfs up some of it, other installed software uses some, and there needs to be some spare memory for caching, etc.
You can install up to 64GB in an Apple Mac Pro. Here’s how.
For large files, the graph shows that the potential performance advantages are huge: CS5 can use 20X the memory of CS4.
On the MacBook Pro, Photoshop CS5 can use only about 1.8 times the memory of CS4, which is plenty for many jobs, but still inadequate for users working with 500MB or larger files.
Virtual memory paging can begin to be an issue around the 5.5GB mark for an 8GB MacBook Pro (allowing CS5 to use 5.5GB), but this varies by system and with Mac OS X changes. So the real world limit is likely somewhere around 5-6GB for an 8GB system, depending on OS version and other programs, etc— experiment.
Even if you have a MacBook Pro with 16GB memory, files can be begin enough to cause the same virtual memory issues.
Virtual memory thus remains relevant on the MacBook Pro, which is why an MPG Pro Laptop with suitably configured SSDs can help: it speeds up virtual memory.
You can install up to 16GB in an Apple iMac (current model with 4 memory slots), or 8GB in older recent models. Here’s how.
On the iMac, Photoshop CS5 can use about 4.7 times the memory of CS4, which is plenty for any reasonable size job. The Mac Pro is a far better investment than a dead-end iMac, but this is a major advantage of an iMac over a MacBook Pro.