Upgrading RAM for iMac retina 5k, 27 inch, 2019

Additional RAM will not speed up boot time, app launch time, file opening time, etc. It only allows more apps to be opened and faster processing on open apps.

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Please download and run Etrecheck.  The free version is sufficient.

Copy the report as shown in this animated screenshot

and use the Additional Text button to paste the report in your reply.

Then we can examine the report and see if we can determine the cause of the problem.

First Check if your Mac needs more RAM in Activity Monitor. If its unitless "memory pressure" graph is consistently "green" then your Mac's performance is not being limited by available memory.

Then read Apple Support article: Install memory in an iMac.

Most PC-centric RAM vendors do not understand the fact Macs are intolerant of memory that does not actually meets Apple's specifications, so I advise buying RAM from a vendor known to support Macs. I am not familiar with the "Lazada" vendor in the links you provided. They simply advertise it as "laptop memory" which does not inspire confidence.

luckeronisek wrote:

I would get these. Corsair SO-DIMM 32GB KIT DDR4 2666MHz CL18 Mac Memory. Better than mixing up RAMs from another brands.

FYI: Corsair RAM has not had a stellar reputation since the advert of Intel-powered Macs in 2006. And yes, I was active here when that PPC-to-Intel transition happened.

Like Kingston, Corsair have two tiers of RAM with different price points based on quality. The higher-priced tier is usually OK in Intel Macs; the lower tier is the problem child.

Unfortunately, as RAM is a very price-sensitive business sector, few resellers stock the higher priced—and more Mac-friendly—versions of either Kingston or Corsair RAM, and adverts are not forth-coming about what series you are ordering.

You have to order from the RAM makers' web sites to get the better grade RAM and that often make it more expensive than OWC's. This is why you virtually never see long-serving contributors here recommend other than OWC.

Crucial does not currently have any compatible RAM for the 2019-2020 iMacs.

OWC has RAM for this model. The OWC RAM is guaranteed compatible with your Mac.

Also, be sure to check "More Info" to see exactly what RAM is currently installed. There are 4 RAM slots, for 16GB they could be filled with either 4-4GB DIMMs or 2-8GB DIMMs.

Crucial RAM (at least genuine Crucial) is not available, the best you can get is OWC (www.macsales.com). iMacs are VERY sensitive to using quality RAM, Corsair and other brands tend to cause issues so please if you upgrade do it right and get OWC RAM.

If the "memory pressure" is always "green" then you'd literally be throwing your money away on additional memory.

Aftermarket PC RAM typically does not perform at its advertised speed. PCs can cope with that, and can adjust their memory bus speed accordingly. Macs can't. I suspect (though I have no way to confirm) OWC tests their RAM for specification compliance, and if that's the case it probably explains the slightly higher price they charge.

Crucial used to sell Mac-compatible RAM that was specifically marked on its packaging. From what others wrote I gather they no longer do that.

I would get these. Corsair SO-DIMM 32GB KIT DDR4 2666MHz CL18 Mac Memory. Better than mixing up RAMs from another brands.

For guaranteed compatibility I would suggest OWC / MacSales.com

https://eshop.macsales.com/shop/memory/imac-2019-27-inch

Crucial and OWC used to be the two "go to" vendors for Mac RAM.

Crucial seems to have gotten out of that business these days. That leaves OWC as the vendor of choice.

Please change Activity Monitor's View option to "All Processes." "My Processes," and it is currently set, may miss some important players.

From your EtreCheck report I see a couple of problems. The lesser is this:

Virtual Memory Information:

    Physical RAM: 16 GB

    Free RAM: 672 MB

    Used RAM: 13.00 GB

    Cached files: 2.34 GB

    Available RAM: 3.00 GB

    Swap Used: 8.32 GB ⚠️

Swap that big is a red flag that some process is not playing well with others. However, this suggests a workaround that may help.

System Software:

    macOS Sequoia 15.0 (24A335)

    Time since boot: About 22 days ⚠️

Although the process causing the high swaps will continue to do so until identified, restarting your computer more often than every three weeks will reset the RAM and keep Swap from taking up half your physical RAM.

OK, the Pachyderm on the Premises is this:

Performance:

    System Load: 2.88 (1 min ago) 2.57 (5 min ago) 2.25 (15 min ago)

    Nominal I/O usage: 20.76 MB/s

    File system: 22.72 seconds

    Write speed: 229 MB/s ⚠️

    Read speed: 2250 MB/s

That will cause slow booting and app launches. A Fusion drive with the specs yours has should be showing Write speeds of 600-900MB/sec. Fusion is not a trouble-free system, and one of its two drive components might be failing, although a File System score of 22 seconds suggests a healthy drive. So this one is a head-scratcher.

Has the computer ever been completely wiped and the OS reinstalled? That can trip up a Fusion system. See it the check a the start of this Apple article shows your drive as "split."

How to fix a split Fusion Drive - Apple Support

I don't see any of the usual suspects. However, you may have a failing HDD in your Fusion drive:

  Write speed: 229 MB/s

   Read speed: 2250 MB/s

It's been 22 days since you've rebooted your Mac. You should reboot at east once a. week or more to clear out the temporary system and application swap and cache files. To start with boot into Safe Mode according to How to use safe mode on your Mac and reboot normally.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Also the Adobe Illustrator is using 114% of the CPU. Make sure you have the latest update for it.

You can download and run the free version of DriveDX to see how the heath of your Fusion Drive is.

If it tells you it's fading an easy workaround for it is to get a Thunderbolt external SSD, clone your boot drive to it with Carbon Copy Cloner  and boot and run from the external SSD. That should get you much faster system performance particularly in the read speed.

If you go the route of the external SSD I recommend you contact the OWC (MacSales.com) Customer Support to see which of their several external SSDs best suit your Mac model, work requirements and budget. OWC is considered by many here to be the premier 3rd party hardware supper for Macs.