Why is my 2016 iMac "Beach Balling" a lot after upgrading hardware? I purchased this system in January, 2016. It says it is a &quot;Late 2015&quot; model. Apple Care told me it is the last generation compatible with non-matching RAM chip amounts so I left the Apple provided 8gb RAM (two 4gb sticks) in when I added 2 8GB sticks of Crucial RAM that is the EXACT recommended RAM specs! I even checked with Apple Care to be sure. &quot;About this Mac&quot; says &quot;24 GB 1867 MHz DDR3&quot; for &quot;Memory&quot;. Anybody have an idea why it's momentarily &quot;beach balling&quot; MORE OFTEN now after adding the RAM?
Prior to adding the ram it was &quot;beach balling&quot; HARD if I ran memory greedy apps like Civ 6 Mac edition so I was forced to hold down the power button then but it ran fine the rest of the time.
To answer the drive type question in the comment, I bought the system with a 1tb non-Fusion HDD as that was the only drive I could afford. (Previous comment was incorrectly based on the 2007 iMac this system replaced.)
As requested the output of &quot;diskutil list&quot; is:
/dev/disk0 (internal, physical):
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      GUID_partition_scheme                        *1.0 TB     disk0
1:                        EFI EFI                     209.7 MB   disk0s1
2:                 Apple_APFS Container disk1         504.0 GB   disk0s2
3:       Microsoft Basic Data Win 10                  496.0 GB   disk0s3
/dev/disk1 (synthesized):
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      APFS Container Scheme -                      +504.0 GB   disk1
Physical Store
disk0s2
1:                APFS Volume Macintosh 500GB - Data  133.9 GB   disk1s1
2:                APFS Volume Macintosh 500GB         11.3 GB    disk1s2
3:                APFS Volume Preboot                 78.8 MB    disk1s3
4:                APFS Volume Recovery                528.8 MB   disk1s4
5:                APFS Volume VM                      12.9 GB    disk1s5
It sounds like you have a dying hard drive, not a memory problem  - not that more memory is a bad thing!  I did some research and according to EveryMac.com your iMac has both an SSD and a regular HDD.  One or both could be dying.  Most of my drives lasted around 5 years and that one is 5 years old now.
I found this post:  https://apple.stackexchange.com/a/239723/377857 on how to fix it, but it seems like you have to remove the glass.  I did a little more research (I want to do this to my iMac) and it seems like you have to cut the glue holding the screen.  That scares me.
Since it is so difficult to do, I would probably use a program like Disk Warrior or Disk Drill (see them recommended by people all over this site) to test out the drive first.  If it's not failing, why go through the trouble of opening it up?
If you do have to change it, it might be a good idea to get a pro to do this job.  Maybe if I get more experience, I will try it myself, but not yet.
PS - In my experience, I've found that using matching RAM modules is the way to go.