Would it be possible to plug-in an external SSD and use that as RAM in iMac

misterkel wrote:

My iMAC is RAM filled most of the time. It has a standard HD, so it's getting pretty slow - lots of rainbow spinning circles.

Would it be possible to plug in an SSD external and use that as RAM / swap file?

Using an SSD as RAM? No. RAM requires a very fast interconnect. As fast as it is, SSD is not that. RAM implemented via Thunderbolt (PCIe) might work adequately, but it’ll still be slower than the built-in RAM. SSD can provide paging and swapping and a place to offload memory contents. Not RAM.

Here is the usual “slow iMac” config: Why is my hard disk drive iMac so slow? - Apple Community

You can use an external SSD as an alternative to the HDD, as linked there. That’s usually the best path here, short of replacement.

Internal upgrades to an iMac 21.5” usually aren’t worth the effort and the costs. And the risks, if you’re not accustomed to disassembling an iMac.

misterkel wrote:

thanks.

iMac (21.5-inch, 2017)

Model Identifier: iMac18,1

Part Numbers: MMQA2xx/A, MHK03xx/A

Newest compatible operating system: macOS Ventura

It's not the storage space - it's the RAM. I have only 8GB. My stupid browser (Brave) uses 10!

I can't find how to correct that.

Unfortunately the 21.5" iMac must be dissembled to upgrade the RAM and that is not an easy DIY project.

see > https://eshop.macsales.com/shop/memory/imac-2017-21.5-inch

To check RAM usage, see > Check if your Mac needs more RAM in Activity Monitor - Apple Support

I might have to switch browsers.

Most third party Browsers do tend to use more RAM than Safari.

First look at your User Login Items and remove any App's that are not necessary.

Then try quitting any App's that you are no longer using to see if that helps.

Can I use an external SSD as a swap file? Or would that be even slower than using the HD?

No, but running from a larger pure SSD (which is faster at swapping) can relieve some of that slow down.

Can I increase the size of the swap file on the HD?

The HD currently has plenty of free space, it's just slow at swapping.

thanks again.

You're welcome.

FWIW those 21.5" iMac's were initially sold for light users. If your demand level has risen to intermediate or higher, then maybe it is time to replace the 21.5" iMac with a new Silicone iMac or at minimum a faster pure SSD model with more RAM.

What iMac model do you have? see > Identify your iMac model - Apple Support

How much free space does it have? see > Free up storage space - Apple Support

An external SSD can not be used for RAM, but it can help to startup and run from an external SSD depending on the spec's of your iMac. see > Use an external SSD as your startup disk … - Apple Community

macOS swaps both to "compressed RAM" and to disk. When macOS swaps to disk, it uses the startup drive. So if you used an external SSD as your startup drive, swapping to it might be faster than with the internal HDD.

As far as I know, the size of the swap file is not subject to user control.

What does the Memory Pressure graph in Activity Monitor show (in terms of green/yellow/red) when you are using Brave or other programs that like to use a lot of RAM?

I would spent no money on that computer. The iMac18,1 is the crippled "educational/institutional" model Apple offered to cost-sensitive bulk buyers with undemanding computing needs.

It has a slow 2-core processor running at 2.3Ghz, where the normal consumer version that year, the iMac (Retina 4k, 21.5-inch, 2017) (iMac18,2) had a four-core processor running at a minimum of 3.0Ghz. The benchmark scores from the MacTacker database tell the story:

For a 18% savings in purchase price you got a 35% loss of performance.

Trying to fix the processor issue is not feasible. The external USB3 SSD option can help some, given that it is a do-at-home project and can cost under US$100 depending on the capacity of SSD you choose.