Den store forskel er vel brugen af LXDE.
Som giver:
System Requirements
We have done many tests and we've found out that Lubuntu can be installed on a Pentium II or Celeron system with 128 MB of RAM, but such a system would not perform well enough for daily use.
With 256MB - 384MB of RAM, the performance will be better and the system will be more usable.
With 512MB of RAM, you don't need to worry much.
The default "Desktop" installer requires 384-800 MB of RAM (depending on selected options.) If you have problems, please use the alternative installer.
Sammenlignet med Ubuntu:
Ubuntu Desktop 11.04 and up uses Unity as the default GUI while the previous releases used GNOME Panel by default. In order to run Unity the system needs a more capable graphics adapter ? see more here or below:
* 1000 ?Hz processor (about Intel Celeron or better)
* 1024 MiB RAM (system memory)
* 3D Acceleration Capable Videocard with at least 256 MB
From experience, we all know that it is recommended to have 2048 MiB RAM to properly run a day to day Ubuntu.
A good start should be with minimum 1024 and recommended 2048 MiB RAM.