My computer has 1GB ram and a very end low graphics card, but I don't know how much power it has.
Unity is very slow on my computer, and I saw that there are many desktop environments which are much lighter and faster, even for a slow computer.
So, what's the lightest desktop environment?
First remove Unity with this command (make a backup before proceeding for safety!):
sudo apt-get autoremove --purge unity unity-common unity-services unity-lens-\* unity-scope-\* unity-webapps-\* gnome-control-center-unity hud libunity-core-6\* libunity-misc4 libunity-webapps\* appmenu-gtk appmenu-gtk3 appmenu-qt\* overlay-scrollbar\* activity-log-manager-control-center firefox-globalmenu thunderbird-globalmenu libufe-xidgetter0 xul-ext-unity xul-ext-webaccounts webaccounts-extension-common xul-ext-websites-integration gnome-control-center gnome-session
then:
sudo rm /usr/lib/thunderbird-addons/extensions/messagingmenu@mozilla.com.xpi
Now, to install Lxde run this command:
sudo apt-get install lubuntu-desktop
or for Xfce this one:
sudo apt-get install xubuntu-desktop
Lastly, reboot and enjoy!
Hope this helped you.
The real answer is: NO Desktop Environment.
Depending on what you want to do, running shell only might be a decent choice.
You can use something like fbterm to split your screen into multiple sections
And there are shell programs that allow you to surf the web, view PDFs and play music as well.
Disclaimer: That isn't my desktop screenshot, My shell only laptop is a work in progress, however I know someone who has successfully set this up, so I know what I'm talking about.
Disclaimer 2: I don't think the shell web browsers play well with Stack Exchange.
As other users have answered, LXDE is the lightest option. My input, however, would be that it definitely makes sense to do a clean install of lubuntu as a whole OS, replacing your ubuntu system.
The lubuntu OS comes packaged with many lightweight programs that maximize efficiency (though you can still install all of your heavier favorites because lubuntu uses the same software sources as regular ubuntu), has very little bloatware, and the entire system is built from the ground up specifically to be lightweight. Also, many of the applications it comes with integrate very well with LXDE specifically. I think that this is the best way to get the most out of low-spec machines.
You can download it here and use unetbootin to make a live CD or flash drive.
There are two major Desktop Enviroments that you could describe as lightweight.
First of all there is Xfce is used by Xubuntu and there is LXDE which is used by Lubuntu.
LXDE seems to be a little faster than Xfce but this little boost costs a lot of functionality. Xfce is also really fast but with more functionality.
There are probably more and better Desktop Enviroments for your purpose but these are the major ones.
If you want the lightest options, I personally love Openbox or Fluxbox!
Check out Crunchbang Linux which uses Openbox as it's default. I have it running on my netbook like a champ!
Short answer: Lxde. For optimal performance install the Lubuntu from the minimal media. You can download it from here: https://help.ubuntu.com/community/Lubuntu/Documentation/MinimalInstall
This question has been answered widely in the forum; Why not try Lightweight-XDE Ubuntu (Lubuntu) ?
Also have a look at these posts:
Lightweight desktop environments
or
lightweight window manager/desktop environment similar to Unity
In each of them you can see lots of suggested/related posts in the right corner of the page.
