RAM upgrade 2017 27" iMac

+1 on OWC. I won't buy Mac RAM anywhere else.

🛑 ⚠️⚠️ However...

The bigger issue is "why do you want more RAM?" The most common cause of slow iMac posts here are NOT RAM-related but caused by slow storage in many iMac models. In that case, adding RAM would not change a thing.

The iMac 2017 5k shipped with either a Fusion drive or an optional NVME SSD. The later is screaming fast—I have that option in my 2017. Fusion drives when working, can be fast but we see a lot of failures with then. Fusions consists of a small fast SSD linked by software to a large, slower mech HD. If one component or the other fails, or the software link is broken, you get vterrible performance that more RAM can't fix.

We can tell quickly whether you are starved for RAM or suffering fomr slow or failing storage from a system config report. Fortunately there is a secure way to do that in this forum setting.

If you want a data-driven evaluation in this setting where we can neither see nor touch your computer, please post an EtreCheck report. We can quickly and within the limitations of these forums help you determine what issues are at play without our playing a protracted game of "20 Questions" with you that could go on for days. 

EtreCheck Pro is available here: https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software issues and interferences, and RAM usage. Etrecheck is the development of a long-serving and trusted ASC contributor. It is a reporting app, not a "fix-it” app, expressly for displaying information in these forums to help us help you remotely. It will not reveal any personal or secure information.

Please see this excellent user tip on how to post long text reports like EtreCheck's into a forum response:

How to use the Add Text Feature When Post… - Apple Community

Please post the entire report. What seems insignificant to a new Etrecheck user can hold answers for those of us who have reviewed thousands of those reports.  

in my experience -- I would not overthink adding RAM to 27" iMac -- add 16gb (2x8gb) minimum to your two empty slots -- 32gb (2x16gb) if you run Photoshop or can afford it -- I run 64gb in my 2017 5k, 128gb in my 2019 5k, 64 gb in my 2019 4k

macsales-com OWC is my preferred RAM vendor

I am fairly sure 2017 hardware will run the faster 2019 RAM spec -- just at the slower 2017 speed -- if you can find original "Apple" OEM ram used (it's pretty easy to spot when correctly described)

adding a SSD (get rid of HDD) is also a desirable upgrade, but you need to remove the screen assembly

adding a thunderbolt 3 external enclosure like ACASIS TBU405 PRO and a M.2 SSD like WD_BLACK 850X will get 2400MBs Read/Write -- clone your boot HDD over to the enclosure and be amazed at the true speed your 2017 iMac can deliver (use the internal HDD for storage)... my 2017 27" came with Apple Flash SSD (no HDD)

Generally speaking anything that that matches the spec (260-pin SO-DIMM, 2400 MHz) and isn't bargain-bin tier will run just fine. Install memory in an iMac - Apple Support

If you are worried about brand shop OWC (MacSales.com) since they some of the best Mac-specific customer support.

I agree wholeheartedly with Allan on using OWC (MacSales.com) only.

I also agree with him on asking why you want more RAM. If it's for speed increase as he said RAM isn't the solution, a faster boot drive is.

Determine your Mac would benefit by installing additional memory first, otherwise you would just be wasting money.

It's very easy to determine if your Mac's performance is being limited by available memory. Please read Check if your Mac needs more RAM in Activity Monitor - Apple Support. If the "Memory Pressure" graph is frequently "red" your Mac will benefit from additional memory. If not, it won't. It's that simple.

Should you determine a lack of RAM is not a performance-limiting factor, EtreCheck will report details that are nearly certain to be helpful.

I neglected to mention this earlier and can't seem t add it to the original post.

Activity Monitor, included in Applications/Utilities on your Mac, might give you a good idea whether you need more memory. you can find information on using it at Check if your Mac needs more RAM in Activity Monitor - Apple Support. I suggest opening it first thing and placing that window where you can access it easily and make sure you are accessing the Memory tab.

Now go about your regular computing tasks. As slowdowns occur check that Memory tab. If the area at the bottom of the window (Memory Pressure) is consistently showing green, lack of memory isn't likely the cause of your issues. If it's consistently yellow upgrade when you find a deal. Red in that area suggests memory is the issue.

I have to agree with the information posted so far.

Allan's advice is almost word-for-word what I would have said if he hadn't beat me to it. I've used OWC for memory, parts, and other advice several times. In fact, several years ago I bought memory for a 2015 iMac because I got a very good deal.

The memory upgrade helped a little with the slowdowns I was having but not as much as I expected. If I hadn't found the memory at such a good price I would have been better off replacing the fusion drive, which was probably the biggest source of the bottleneck. paying for the new drive and installation was out of my budget at the time so I took a chance that improving the memory would solve the problem.

If you decide to add more memory make sure you choose a reliable vendor and understand their return policy. It's important that the memory is in spec or you're likely yo have issues.

I have to agree with the information posted so far.

Allan's advice is almost word-for-word what I would have said if he hadn't beat me to it. I've used OWC for memory, parts, and other advice several times. In fact, several years ago I bought memory for a 2015 iMac because I got a very good deal.

The memory upgrade helped a little with the slowdowns I was having but not as much as I expected. If I hadn't found the memory at such a good price I would have been better off replacing the fusion drive, which was probably the biggest source of the bottleneck. paying for the new drive and installation was out of my budget at the time so I took a chance that improving the memory would solve the problem.

If you decide to add more memory make sure you choose a reliable vendor and understand their return policy. It's important that the memory is in spec or you're likely yo have issues.