[awiesenhofer]

Unfortunately not the biggest one though. I too have a old 2012 macbook pro with hdd. While it was flying under snow leopard it now grinds to a halt every time i open any app or document. Already ordered an ssd but still dreaming of downgrading it back to snow leopard.

[tssva]

Microsoft Windows used to be notorious for slowing down over time. A fresh OS install would restore performance. Many would recommend doing a fresh Windows install yearly to maintain performance.

I have a late 2012 MacBook Pro Retina with a SSD and unfortunately notice the same decreased performance over time with macOS. A fresh OS install breaths new life into the machine.

When you get your SSD do a fresh OS install instead of restoring the complete HD to the SSD.

[trevyn]

Or just clean out your random LoginItems and kexts and whatever now and then. Check Activity Monitor and uninstall anything running that you don’t need.

[ryacko]

Could be that the rewritten areas for the OS are showing some wear, requiring multiple reads.

Cause and effect is ambiguous because it is so transparent, one doesn’t know what interrupts where are taking the most time.

[planb]

Might also be that newer versions of macOS need more RAM than Snow Leopard and therefore less is available for filesystem caches.

[lloeki]

This might be a factor although IIRC there has been some work after Lion (Mavericks?) where OS RAM usage went down significantly. It was really noticeable on 2GB VMs.

[saagarjha]

Mavericks introduced compressed memory, so that may be the improvement you’re talking about.