Memory Makes the Photoshop CS5 Scratch Drive Irrelevant

Use 70% unless testing proves more is faster

With the advent of 64-bit Photoshop CS5 for Mac, performance is simple—

Install enough memory, and Photoshop will scarcely touch the scratch volume.

Install 24GB memory for set-and-forget, or 16GB on systems for which that is the limit.

See discussion on the Photoshop CS5 Memory Use setting.

How much memory is enough?

Enough is when:

• There is no virtual memory paging;
• Photoshop does not need to write to the scratch volume; it can keep everything in memory.
• The system still has several gigabytes of memory for drive caching.
• Other needed programs can be run at the same time with the above still true.

Few users need more than 24GB, and for many users, 16GB is enough.

Buying memory

Apple won’t sell you 8GB memory modules as of Jan 2011, so get your memory at OWC, and enjoy 4X the memory for the same amount of money (as of Jan 2011). See this Dec 2010 discussion.

Recommendation for 4/6-core Mac Pro

Optimal memory for 4/6-core Mac Pro — three modules

The 4-core and 6-core Mac Pro can take up to 32GB as four 8GB modules in four memory slots.

But CPU performance is 2-3% faster with three (3) modules, which is 12GB or 24GB. Go to 16GB or 32GB only if needed.

Recommendation for 8/12-core Mac Pro

Optimal memory for 8/12-core Mac Pro — six modules

The 8-core and 12-core Mac Pro can take up to 64GB as eight 8GB modules in eight memory slots.

But CPU performance is 2-3% faster with six (6) modules, which is 24GB or 48GB. Go to 32GB or 64GB only if needed.