- A well-supported mainstream desktop distribution. (Basically one of *buntu, Fedora, OpenSUSE, or Mageia.)
- A full desktop environment. (Unity, Gnome, KDE.)
- Any computer with less than 2 GB of RAM, or built before 2008.

I have been using Ubuntu on my main laptop (dual-core Pentium D, 2 GB RAM, Intel 965 GMA graphics) for a while, and I have found it almost impossible to use with anything heavier than Openbox. Run it with Openbox, it's fast; run it with Unity and the sluggishness is dire. The situation is similar with my other computers; none of them are usable with modern compositing desktops.

What's happening here? Are the requirements of modern desktops really that huge, or am I missing something?

(I will note also that graphics capabilities aren't the only bottleneck; otherwise KDE wouldn't take 30+ seconds to log in...)

I have a Dell XPS M1330 that was new in 2007 (T7250m, 2 GB, Nvidia something or the other graphics, 80 GB 5400 rpm drive). While I have upgraded it NOW to a T8300m and 4 GB ram, it originally had only 2 GB. It even with 2 GB ran the latest Mageia or Debian SID w/ liquorix kernels and KDE without any issues.

Hmm, hadn't tried the Liquorix kernel. That seems to improve responsiveness a little bit, although the fans are still stuck at full blast when I use Unity; and the stupid alt-tab dialog still takes ~5 seconds to appear. Thank you though!

I have a 3.4 gig pentium D running on slackware 64 current, 4 gigs of ram and tho slackware isnt known for being a desktop distro it has all the kde bells and whistles. KDE runs as well on it as what KDE is trying to emulate, MS Windows, but the reason i use linux is that MS windows performance level isnt good enough.

The kind of performance i want in a window manger and what ever bells and whistles i want to run it with is instantaneous and i have yet to use a DE on any hardware, cutting edge or not, over the last 15 years or so of linux use, that could cut it. If you want really good performance, find a window manager you like and get creative constructing a personalized environment based around it.

That's the thing though, Windows 7 performance is far superior on the same machine. It has much more RAM than I typically fill up, it runs Windows fine, why can't it run Unity fine?

This is what I've been doing for some time. It works, but it would be more desirable for everything to work out of the box, instead of me having to cobble up my own desktop.

Edit: to make it clear, I'm not using Windows as my main OS because it's developer-unfriendly. Try doing anything on it with third-party libraries... ugh.

All i have to contribute then is that you may be short of ram. With fluxbox, rox filer and 2 browsers with a few tabs open atm im using 1807 megabytes of ram. KDE is a real hog with memory you'd probably have better luck with xfce.

Check what system services you are running, too. There may be many processes running that you don't really need, that are eating up RAM. I find this to be particularly the case with the *buntus.

I run Slackware 14 Xfce 32-bit on a desktop machine with an AMD Athlon 2000+, with 768MB of RAM, and its pretty zippy for an old processor with little RAM.

In my experience, Debian with either Xfce or LXDE, even with Gnome 2 (those days are gone with Wheezy), runs really well with low spec machines.

Most of that is probably cache. Linux caches stuff aggressively but will free it up to make room for running programs.

If it's not cache, one of your programs probably has a memory leak.

(In my case, Openbox plus Firefox with half a dozen tabs usually takes about 200 MB of RAM, not including cache. With Unity it's more like 400 MB. This is still well below 2 GB, with lots of room for cache.)

Hmm, haven't really tried disabling services on Ubuntu. Upstart seems designed to discourage that.

I have tried disabling everything I didn't need on OpenSUSE and Fedora (12.3 and 18 respectively). That might have shaved 1 second off the boot time, if it did anything at all. Kind of weird, isn't systemd supposed to be faster and generate less overhead than sysvinit et al?

I've recently run Debian, Slack, and Arch on a Pentium II laptop with 192 MB of RAM. With a few modifications to default settings (mostly stuff like outline move/resize), Xfce worked quite well. Xubuntu won't even boot on such an old computer.

My desktop has an AMD Sempron 2600, 1.1GB, and motherboard graphics. It runs CentOS and I also use it for testing the distros I review. Ubuntu is unusable and OpenSUSE sluggish, but PCLinuxOS ran KDE well last time I tried, and Gnome3 was usable in fall-back mode with Arios and Pinguy. Personally, I prefer Mate and Xfce anyway.

My laptop is an IBM Thinkpad with a Pentium M, and it runs Salix with Xfce.

I run a flash drive with OpenSuse 12.3 KDE on some old stuff. Seems to be OK.

Appearances might be deceptive there. Flash drives have terrible throughput and bog down under I/O load, but
- they don't suffer from seek delays
- writes go to tmpfs instead of the hard disk
- live distros are compressed, which reduces I/O
The upshot in my experience is that desktops perform better on live flash media than they do once installed.

Thanks for reminding me of this though, because it clarifies the problem. If a compressed live image on a flash device runs faster than an uncompressed hard disk install, the bottleneck is almost certainly disk I/O.

Your laptop might be able to have some tweaks to improve speed. As you say, the bottleneck is someplace usually more than everywhere. That system doesn't sound too bad. May be some bios setting for too much or too little graphic shared. Might be some driver issue. Could be as you say, I/O. Could be dma or other issue on drive. Could be speed on processor or acpi issue. Laptops have never been great systems for speed. Making swap on the flash drive may even speed it up when using hard drive installs.

Compressed files being used for root can show up faster. You might even look at ram or load to ram type distro's.

For fun you could try stuff made for older hardware. Slitaz and Wattos might be useful to you. Others may suggest equally good like crunchbang or Slax or (I think) Antix.

Gave Fedora 18/Gnome 3 a try... I
- Set swappiness to 1. I know I'm not supposed to do this, but this machine has 2 GB of RAM, and applications never use more than 1 GB from what I've seen. Swapping should never, ever be necessary during normal desktop usage with that much RAM.
- Went through systemctl and disabled every single .service entry that I did not have a pressing need for, about a dozen entries in total.
- Disabled transparent hugepages via the bootloader. This kernel feature is, in my experience, a source of much misery on desktops.
- Installed a nice fully animated cursor theme. Busy cursors are underappreciated on sluggish desktops.

This brings boot/login time down to 40 seconds total, about on par with Windows 7. The desktop is more usable than it was, but still feels kind of laggy. Might be in part due to drop shadows in Gnome 3 - I'll note that translucency in Windows 7 does the same thing on this chipset, maybe the hardware is bad at alpha blending.

Next step: dusting out the laptop...

P.S. The busy cursor doesn't seem to work as it does on Windows; it only appears when an application is launching and the mouse is over the desktop. More X11 mess here? Is this what "startup notification" is about?

Turned out there was a lot of dust on the heat sink... Thus the fan noise. Fan is now running very quietly thank you, and performance is much better.

Note to self, be more proactive about keeping the computer dust free.

Sounds like you are on the right track. It is never easy to track down issues. Simple stuff has gotten me a few times.