Imac running slow and not all memory is showing as used in Activity Monitor

Whoa! Let's back up.

Your symptoms do not suggest more RAM is needed but rather that you have the slow, factory mechanical hard drive used in 21.5-inch iMacs from 2012 through 2019. Those drives were glacially slow even when new, and the cause of over 90% of "slow iMac" complaints here. If that is the case, no amount of RAM will make it better.

👉🏻 However the larger issue is that you have the crippled "educational/institutional" iMac from 2017, intended for bulk buyers with minimal performance needs. The clear evidence lies in the INFO window you posted:

• It does not include the descriptor, "Retina 4K"
• the processor shows as a slow, laptop-class 2.3ghz DUAL-CORE.

The standard consumer model of the 21.5-inch 2017 iMac would include "Retina 4K" in the name, and have desktop-class FOUR-CORE processor running at a minimum of 3.0ghz.

These are benchmarks from the MacTracker database showing the score of the two models. Yours is on top:

As already pointed out, if you have the factory mech hard drive, the only thing that can make your "edu-iMac" feel faster in a cost-effective manner is to use a external solid-state drive (SSD) as the boot volume.

To put some dimensions on the level of improvement: The base hard drive in most edu-iMacs could move data only at 70-80MB/sec even when new. The cheapest external SSD boot volume option will do 400MB/sec, and can be set up at home for under US$100 with no pro help required.

See: Use an external SSD as your startup disk … - Apple Community

Additional RAM will not speed up boot time, app and document open time. It only lets more documents be open and processed at the same time. Please run Etrecheck and post the entire document in your reposes as follows:

Copy the report

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.

At this point I suggest that you run an EtreCheck report, and optionally post it here if you need assistance with interpreting its results. EtreCheck is a free troubleshooting tool, developed by a valued forum member, that greatly assists with analyzing issues with Macs.

Just looking at what you posted, my guess without the report is that you have an iMac with potentially insufficient RAM or running a slow 5400 RPM HDD.

Ref: Using EtreCheck to Troubleshoot Potential Mac Issues

SweatTee wrote:

That is what I have been considering - adding more RAM and this has to be done by a repair company (can't do it yourself on this version of mac) and moving to an SSD. Just not sure if these upgrades are worth the investment considering my mac is from 2017. Any thoughts on the value add on the upgrades?

I would not pay someone to do the surgery needed to add RAM to a 21.5" iMac, based on the screen shots you posted. There are things for which it is useful to have more than 8 GB of RAM – e.g., doing heavy video editing; running virtual machines – but there's no evidence that at the time of the screen shot, you were being limited in any way by the 8 GB of RAM that you already have.

Moving to a SSD is something that is

• Much more likely to provide a performance benefit, and
• Much more practical economically

Your Mac has USB-C (USB, Thunderbolt 3) and USB-A (USB 3) ports, which are compatible with a wide range of modern external SSDs. No need to perform expensive surgery to replace your internal drive (assuming that it is not actively failing). Get an external SSD, clone your current system onto it, and make the external SSD your new startup drive. You can do that at home with no expensive, inconvenient repair shop trip required.

Plus, an external SSD would be potentially reusable for backup storage or extra storage once you got a new Mac.

Whatever the problem is, it's certainly not a lack of memory. Besides, the symptoms you describe are not consistent with that assumption. It's probably a failing hard disk drive, but without any additional information that's just a guess.

Post the EtreCheck report.

You haven't told us what the Memory Pressure graph in Activity Monitor is showing (in the way of greens, yellows, and reds) – but it looks to me like your system has enough memory for what it is doing.

According your screenshots,

• You have 8.00 GB of RAM. 3.82 GB is in use for things that have to be there. macOS is putting another 2.55 GB to work to cache stuff – just in case your applications ask for that stuff again, before they ask for more memory. But that cached stuff can be dumped, and the 2.55 GB can be freed, in a heartbeat. 1.63 GB of RAM is unused, and is not doing any work for you at all. But that also means your system wasn't hurting for RAM at the time you took the screen shot.
• Swap used is 0 bytes, which means that your Mac hasn't been swapping the contents of memory to your startup drive in an attempt to (slowly) simulate extra RAM.
• Compressed RAM is non-zero, which suggests that perhaps at one time, the Mac might have been under some mild pressure to provide more RAM than it actually had. Even here, the amount of compressed RAM – and the fact that swap used is 0 bytes – suggests that you never really stressed RAM hard enough to hurt performance by any noticeable amount.

I'd look to something other than "running out of memory" to explain the performance problem.

To be honest, if it were me, your 2017 Mac cannot be upgraded, software-wise, past macOS Ventura. As such, I would consider either getting a 2023 M3 iMac or a 2023 Mac mini (along with a monitor) going forward.

Both RAM & the system drive are upgradeable, but as you know, it would require opening the Mac. Even with these upgrades, your Mac will still be macOS limited. Apple supports the newest three versions. Currently, that is (newest to oldest): Sonoma, Ventura, & Monterey ... so your Mac would be in the "middle" for software updates.