Is the latency of stock 2019-20 iMac RAM CL18 or CL19?

[And, relatedly, is there anyway to check this if you have the stock RAM?]

This thread ( says the 2019 & 2020 iMacs need CL19, citing Apple as a source:

Consistent with this, Crucial’s Mac-specific aftermarket RAM sticks for the 19-20 iMac are CL19:

Kingston also recommends CL19 for the 2019 and 2020 iMac; 2019 link shown here:

Indeed, that seems to be the case for nearly all RAM vendors.


1) The provided link to Apple Support doesn’t actually provide any info. on latency requirements. So there’s no CL19 specification there.

2) OWC’s RAM for the 19-20 iMacs is CL18. I called OWC Tech Support, and they say that’s what the Apple OEM RAM is as well:

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So what’s going on? Why do most aftermarket RAM vendors recommend CL19 for the iMac, even though OWC says the latency of OEM Apple RAM on those machines is CL18 (and thus spec-d out its own RAM to be CL18 as well)?

Pure speculation, but here’s a guess: Apple’s OEM RAM is actually CL18. However, getting CL18 to run on the Mac requires very stringent RAM QC and thus, to avoid failures, most vendors recommend their CL19 RAM instead.

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