Adding RAM to my iMac

If your iMac is the 27" 2019 model, then you can max that RAM at 128GB.

Install memory in an iMac - Apple Support (CA)

Most veterans here will recommend that you purchase your RAM from OWC/macsales.com

or Crucial.com because they have quality product and very good support.

Macs can be especially sensitive to flaws in RAM product, so best to buy quality from know sources.

If you can get by with 16 or 24 GB of RAM just order two 4 GB or 8 GB modules and put them in the empty sockets. I have 16 GB RAM and just added two 4 GB modules. Works like a charm. The only time I saw any slowdown was when I was trying to edit a 500 MB+ image with the retouch tool in Photoshop Elements.

However, adding more memory will not make the iMac faster in booting, opening apps or documents. More memory only allows more docs to be open at one time and processed.

If you have the Fusion Drive that would be the bottleneck in the boot time or app/document open time. To get around that using an SSD as your boot drive would speed that up quite a bit. I use one for beta system testing and it boots about as quick as my internal SSD does (around 30 seconds or so)

Please visit macsales.com, they can tell you if RAM is available for your machine and if it is they will have install videos for it. Imho I would replace the iMac with 16gb of ram. Far more simple and possibly less expensive than your idea.

You're welcome.

Yes. That iMac has only four RAM slots, so it makes sense that you may wish or need to remove what is already there and replace with new to reach whatever capacity you wish.