How to upgrade 2019 Imac

MrMadsenDK wrote:

I have the iMac (Retina 5K, 27-inch, 2019) with 8 GB ram and a fusion drive.

I would like to upgrade. is it possible to buy an extern fast SSD and use for main harddrive, through some kind of extern connection?

Yes. Your iMac has

• Four USB-A ports that support USB at up to 5 Gb/s
• Two USB-C ports that support USB at up to 10 Gb/s or Thunderbolt 3 at up to 40 Gb/s

iMac (Retina 5K, 27-inch, 2019) - Technical Specifications - Apple Support

So you can use

• USB / SATA SSDs (cheapest, slowest)
• USB-C (USB 3.1 Gen 2) / NVMe SSDs (a lot faster for only a bit more money)
• Thunderbolt 3 / NVMe SSDs (fastest, but significantly more expensive because of the cost of the enclosure)

You can get external SSDs pre-assembled, or buy an enclosure + a notebook drive or M.2 circuit board stick to assemble one with components of your choice for yourself.

Would 8 more GB ram, do a fair speed boost? :)

Depends on what sort of workload you are running now. If you run Activity Monitor, with the Memory tab open, while you are doing things that would tend to use a lot of memory, the color-coded Memory Pressure graph and Swap Used figure can give you some hint as to whether extra RAM would do you any good – or not.

Yes, it's likely that you would benefit by installing an external SSD and using that as your startup drive.

It also as likely that bumping the RAM wouldn't give much of a performance boost.

Before doing either of those things, you might run a diagnostic utility to see if it can be determined why your Mac may be underperforming. It could be anything from an unintentional malware installation to a hardware bottleneck or failure such as a split Fusion drive. Some things are fairly easy to fix.

Please run an EtreCheck evaluation of your Mac and post the generated report back here in a reply. EtreCheck is a safe and highly regarded utility from a trusted developer and respected ASC contributor. The diagnostic report will not include any personal info. It simply gathers specifics about hardware performance and installed software that might be in conflict with the OS.

Please navigate to EtreCheck.com and download the free version. Be sure to Allow Full Disk Access when you install the app. Once you’ve run the app and created your report please post it with your reply to this message. 

Please note you must upload the full report. To see how, please click >  How to use Add Text when posting… EtreCheck Report.

We’ll use your EtreCheck report to look for the things that may be causing your problem and advise how to correct them.

How to use external SSD storage, and how to upgrade internal memory:

• Use an external SSD as your startup disk … - Apple Community
• Install memory in an iMac - Apple Support