I am running F39 on an old iMac. It’s a low spec model, i5 and only 8GB RAM. It ‘works’. but it’s a bit laggy, sometimes 5-10 seconds opening apps or switching between apps.
I can live with it, but wondered if upping the RAM to 16GB ram will likely help? Not sure if that’s futile, if it’s more due to processor than RAM, don’t understand hardware very much.
My spec is below, grateful for any opinions:
Is it an SSD or a HDD ? If you have an HDD, an SSD is infinitely better feeling.
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yes, if hdd, that would probably be the most noticeable bottleneck, and if you have a bunch of tabs open in your web browser, the OS may be having to use swap, and if it’s a hdd, that’s going to be very slow. I would use htop. ps_mem or similar to watch what is happening in regards to cpu and ram. iotop may help for the hdd/sdd usage. If the browser is using too much ram, you might check out Auto Tab Discard addon for firefox, or maybe similar addon for other browsers.
meant to reply to op…
I have the iMac14,2 with 8GB RAM booting from a USB3 SSD (external case with a drive pulled from a Windows system that needed more space, so not expensive several years ago). My model has Apple’s “hybrid” system consiting of a very slow 1GB hard disk and a small SSD that is now dead. I use the internal disk for backups. I worked in a shop that moved to iMac14,1 from SGI workstations. We used large firewire/USB3 hard disks for data. They were faster than the internal HDD so booting from external drives was often done to have access to multiple MacOS versions.
With a low spec model you might be happier with a more lightweight DE instead of GNOME. LXDE, Mate, XFCE would suit this.
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Sorry, stupid of me to omit that. It is an SSD, not HDD
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That’s an interesting thought. Forgetting the performance issue, I have been meaning to ask, is it possible to have two DE’s installed, so I can choose between? I was going to try KDE out. (Again, ignore the thread title for this question, as it relates to another machine!)
This machine (I think) has 2 RAM slots. that means it probably has 2 x 4GB sticks. I will need to buy 2 x 8GB sticks, which won’t be expensive but probably won’t be cheap either. I will do it if anyone thinks it will make SOME kind of difference, but if it’s likely to have no effect at all I won’t bother!
This discussion makes no sense without knowing how much available RAM you have under your normal workload. If it’s close to zero, first add swap file, then add more RAM. But if you have free or available RAM during normal operation, RAM is not the bottleneck.
I recommend collecting some data / graph about RAM/Zram/Swap usage first and then we can discuss if it may be a factor slowing down your system.
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I believe 8 GB is fine as long as you aren’t playing video games, compiling stuff, or doing anything high-memory usage. With about a dozen Firefox tabs up on Fedora I can barely get 4 GB usage. On Windows 10 right now with Steam and 12 Firefox tabs up I’m at 5 GB. I imagine Chrome under average conditions might take it up to 6 GB.
I suspect by the time 8 GB becomes a problem, you’ll have apps or the desktop session close randomly from OOM killer, so if that hasn’t happened yet, you’re good to go!
I don’t think adding additional RAM is going to improve performance.
Did you do anything with the SSD prior to installing Linux? If it’s a decently-used SSD or was ever near-full, it might need cleaned-up/fully trimmed. I have some notes here about it, and before I reinstall an OS I boot to an openSUSE Tumbleweed Xfce LiveUSB to wipe my SSD with those commands. I’d do this as a last-resort unless you want to clean-install (this fully-wipes the drive)
If you’re doing full-disk encryption, I’d check this out: Full disk encryption performance can be really improved in NVMe and SSD devices
I don’t know if default partitioning has any effect on performance, but I’d immediately suspect something with CoW and Btrfs if that’s what you’re using and if the slowness happens when disk drive read/writes occur. I always do Custom → Standard → and something else for the root / partition (ext4, XFS, or F2FS depending on what I feel like trying 
) along with removing /home so everything is on root. For all drives I’d use XFS, but F2FS for NVMe.
I don’t believe GNOME would be affecting performance negatively enough to notice on that hardware also. I’d try GNOME on Xorg (bottom-right gear at log-in) to see if it performs better than Wayland.
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That probably makes a lot of sense, to others. I don’t know how to do any of the things suggested, so I have to make a more ‘dumb’ decision/guess here. I have no clue how to analyse RAM usage or what a Swap file even is, unfortunately.
It is possible. With lightDM as displaymanager you can then select which Desktop Environment you want to start. You can do that with GDM as well, but that one is slower.
Thanks, most of that was above my pay grade but some was quite useful even for me. I use Brave rather than Firefox, if that makes a difference
Monitor the output:
free -h; swapon -s; zramctl
Specifically when the lags happen.
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There have been problems with cheap SSD’s that are really flash cards in an SSD case, including some that look like and are sold as high-end SSD’s from Samsung and probably other expensive brands. As others have mentioned, you need to collect some data. Linux has excellent performance monitoring tools, but it has been over 5 years since I used them, so can’t say what iare currently the preferred tools.
Monitor your resource usage with top, htop, whatever monitor you use. I suspect your CPU/GPU is the biggest bottleneck however keeping track of these numbers will give you a better idea of what’s bottlenecking your system than my or anyone else’s speculation.
My two cents.
I use two PCs with low end CPUs and 4 Giga of RAM.
Mostly I browse the Web, watch Youtube and some other videos, write email, some blogging, some basic image editing, some office work.
Both PCs are fine with Fedora Gnome (workstation), not snappy but doable.
It depends on what you want / need to do on the PC.
Take it for granted, when you need to do serious work like video editing, 3D modeling, maybe programming or you want to play current games, you need a new computer.
When you want / need to use an old computer you cannot do the above things, you must lower your expectations.
Adding RAM makes your life a bit better but doesn’t make a whole big difference.
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If @boredsquirrel were here, he’d tell you to run everything in RAM . . .Even though I slightly agree. . . 
:
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Adding RAM will automatically turn some things from “extreme mode” to more normal.
Like Fedora KDE Kinoite uses about 6GB of RAM for me, if there is that much.
It would also run on 4GB, but this may mean more compression, more persistent storage read/writes (and wear) etc.
12GB is the sweet spot as I never use that much, only when running VMs.
But yes @hamrheadcorvette if the OS would be smart it would cache more into RAM, especially when people have 16/32GB
I totally tried toram on a few distros after I heard about it
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