Mixing Ram Sizes in 2017?

[tekboi]

Hi All,

I'm currently looking for RAM to add to my Late 2017 iMac. It currently has 8 gigs and i'm looking to add another 16 gigs and total it out at 24 gigs of ram. So we're looking at two 4 GB chips and two 8 GB chips after this is done.

One of my co-workers who is smarter than I am suggested that I NOT mix ram sizes because it causes a decrease in performance. Is this true?

Here is the specific RAM cards that i'm looking into buying...
https://www.amazon.com/gp/product/B01BIWMWVS/ref=ox_sc_sfl_title_3?ie=UTF8&psc=1&smid=A2NDNAPHQ3UDKH

 

[tubeexperience]

Mixing RAM size is not a problem.

Mixing timing and voltage could be a problem.

 

[mreg376]

Hi All,

I'm currently looking for RAM to add to my Late 2017 iMac. It currently has 8 gigs and i'm looking to add another 16 gigs and total it out at 24 gigs of ram. So we're looking at two 4 GB chips and two 8 GB chips after this is done.

One of my co-workers who is smarter than I am suggested that I NOT mix ram sizes because it causes a decrease in performance. Is this true?

Here is the specific RAM cards that i'm looking into buying...
https://www.amazon.com/gp/product/B01BIWMWVS/ref=ox_sc_sfl_title_3?ie=UTF8&psc=1&smid=A2NDNAPHQ3UDKH

I assume you mean a "mid-2017" iMac. Your co-worker is thinking 1980's. As long as the RAM is from a quality manufacturer and according to spec you're good. Some argue that adding RAM in pairs (as you're doing) is superior to adding just a third module, others disagree. But in any event you're good to go.

Also, Crucial sells RAM that they say has been specifically tested on Macs. It's a few dollars more. That's what I usually buy, have had 100% success with it, but cannot swear that I wouldn't have had 100% success with their other, non-Mac tested similarly spec'd RAM:

https://www.amazon.com/Crucial-8GBx...id=1532088318&sr=1-2&keywords=crucial+for+mac

 

[theluggage]

One of my co-workers who is smarter than I am suggested that I NOT mix ram sizes because it causes a decrease in performance. Is this true?

Not if you install RAM a matching pair of modules in the two free slots (2nd and 4th slots) - which is what you're proposing to do. Other permutations will probably work, but you'll lose dual-channel mode which does have a measurable effect on performance.

The "Memory" page in "System report" when you're done should look like this:

BANK 0/DIMM0:
Size: 4 GB
...

BANK 0/DIMM1:
Size: 8 GB
...

BANK 1/DIMM0:
Size: 4 GB
...

BANK 1/DIMM1:
Size: 8 GB
...

There's a lot of wrong/confusing/ambiguous advice out there but various MacRumours users thrashed this out in a thread a year or so back: for dual-channel, one matching pair of modules goes in the two "DIMM 0" and another matching pair go in the the two "DIMM 1" sockets.

For peace of mind, I'd stump up the extra 10% and buy the RAM directly from Crucial using their online RAM-finder tool, which gets you a kit explicitly sold as an upgrade for your Mac model. (Note that last time I looked they recommended different chips for the entry-level i5 c.f. the other 5k models).

 

[colticus]

IM running that same exact setup in my 2017 iMac and it recognizes the additional ram and I haven't experienced any problems.