Installation/SystemRequirements

Ubuntu Desktop Edition
2 GHz dual core processor
4 GiB RAM (system memory)
25 GB of hard-drive space (or USB stick, memory card or external drive but see LiveCD for an alternative approach)
VGA capable of 1024x768 screen resolution
Either a CD/DVD drive or a USB port for the installer media
Internet access is helpful

Screen resolution will be set at the highest your graphics card can handle but when you boot-up you should be given a "Low graphics mode" option which allows you to set it to something better for your monitor.

On one hand, hardware produced in the last few years or with an efficient architecture or machines built for a specific purpose can often work well with less. For example, a netbook with an 8 GB SSD will work well although there wont be much room for saving stuff directly onto the drive so cloud storage services could help a lot. A machine with a crumbling, 15 year-old, slow, 8 GB, IDE hard-drive probably won't work and doesn't really compare with the netbook anyway. It might be worth trying Ubuntu but really start looking at other distros. On the other hand, some GNU/Linux distributions may require more powerful hardware as minimum system requirements, like the Ubuntu GNOME case.

All 64-bit (x86-64) CPUs should be fast enough to run Ubuntu and can run the 32-bit (x86) version as well. For an optimized installation (and especially for those wishing to run more than ~3 GiB of RAM) however, a 64-bit installation CD is available. The 32-bit version tends to be easier to use and runs into less problems. 32-bit ISO images are no longer being produced (as of 17.10).

Ubuntu Desktop 11.04 through 17.04 uses Unity as the default GUI while the previous releases used GNOME Panel by default. From 17.10 onwards the desktop uses GNOME Shell. In order to run these environments the system needs a more capable graphics adapter – see more here or below:

4096 MiB RAM (system memory) for physical installs.
2048 MiB RAM (system memory) for virtualised installs.
3D Acceleration Capable Videocard with at least 256 MB