My 2017 iMac has always been slow, why? New iMac Specs:


Mid-2017 iMac
Retina 4K 21.5 inch
3.0GHz quad-core Intel i5 CPU
AMD Radeon Pro 555 with 2GB Memory
1TB Hard Drive
8GB RAM


macOS Catalina 10.15.2

It keeps hanging, lagging or freezing with the rainbow cursor for 1 or 2 seconds. Sometimes, even YouTube and Apple Music stops playing for the same time. 

It's slow in everything, not just loading/writing on hard disk. I have tried a fresh installation of macOS with no results. 

The memory is always empty and 70% of CPU stays in idle. I see no peak in usage on Activity Monitor. The hard disk is not full either. It's just strange. Has this been happening to anybody? 

It has been like this forever. Having had a MacBook, I have never really used this machine except for now that I am home all the time. 

Here is the report generated by EtreCheck: https://pastebin.com/4hbaLGte
It was indeed a Hard Disk issue. I have bought a Crucial SSD from Amazon and a USB 3.0 to SATA III connector. Since then, I have been using this configuration with the macOS being installed on the external SSD. I get r/w speeds of 480 MBps. The Mac runs magnificently. Nothing to complain.