Memory Performance Tips

katsura · Post by **katsura** » Sat May 23, 2020 6:54 pm

Use all available channels. If you have a Mac with a two-channel memory controller, use at least two memory modules so that two channels actually get utilized. Wikipedia: Multi-channel memory architecture.
Use the fastest supported memory clock modules. If you have memory modules that are lower clock speed than Apple officially supports, you definitely want to replace your memory modules with the ones that are at officially supported memory clock. Some Mac models may support higher than the officially supported memory clock speed*. I use EveryMac.com to find the officially supported memory clock speed and size. For example, EveryMac.com: DDR3-1333 for MacBookPro8,2 (Late 2011).
Use low CL (CAS Latency) memory modules. Tom's Hardware: The lower the CAS latency, the better.

* For example, according to Intel specs, MacBook Pro (15-inch, Late 2011) MacBookPro8,2 Intel Core i7-2675QM 2.2 GHz supports DDR3 1066/1333 MHz, and MacBook Pro (15-inch, Early 2011) MacBookPro8,2 Intel Core i7-2720QM 2.2 GHz supports DDR3 1066/1333/1600 MHz even though Apple ships with DDR3 1333 MHz. To be confirmed.

How many channels does my Mac have?

All Intel Core i3/i5/i7/i9 Macs have two channels. iMac, Mac mini, MacBook, MacBook Air, and MacBook Pro. Older Macs (Core 2 Duo, Core Duo, etc.) didn't have the multi-channel memory architecture, I assume.
MacPro7,1 (2019) : six channels
MacPro6,1 (2013) : four channels
MacPro5,1 (2010/2012) : three channels per processor
MacPro4,1 (2009) : three channels per processor
MacPro3,1 (2008) : one channel? Memory Installation Manual
MacPro2,1/1,1 (2006/2007) : one channel? Mac Pro Memory Installation Instructions
iMacPro1,1 (2017) : four channels

DDR-1600 4GB x 2 on Macmini5,1 (using two channels. 20.35 GB/s):