Ubuntu Desktop

The main flavour of Ubuntu using Unity (16.04) or GNOME Shell (17.10 and newer).

Minimum

• Xenial Xerus (16.04)

  • 700 MHz processor (Intel Celeron or better)
  • 384 MB of system memory (RAM) for 32-bit
  • 512 MB of system memory (RAM) for 64-bit
  • 8 GB of free disk space
  • VGA capable of 1024x768 screen resolution
  • Either a DVD drive or a USB port for the installer media

• Bionic Beaver (18.04)

  • at least 1 GHz 64-bit processor, given that 32-bit desktop live was discontinued
  • at least 1 GB of system memory
  • at least 9 GB of free disk space
  • other requirements may follow the "Recommended" section

The minimum requirements were last mentioned in 12.04 release note, and has since not found in release note of newer releases. The minimum requirements for newer releases are unofficial and subject to testing on real hardware or in a virtual machine (VM). Ubuntu has varying requirements on VM.

Bionic Beaver (18.04) on VM: Requires VT-x/AMD-V hardware acceleration. Requires at least 1156 MB RAM and 128 MB video memory, but disable 3D acceleration for at least usable desktop to open menu and change settings. This is the practical minimum for a test drive, but not for daily use.

Recommended

• Xenial Xerus (16.04 64-bit)
  • 2 GB system memory
  • other requirements are similar to the following
• Bionic Beaver (18.04 64-bit)
  • 2 GHz dual core processor or better
  • 4 GB system memory (since 18.04.2)
  • 25 GB of free hard drive space
  • Either a DVD drive or a USB port for the installer media
  • Internet access is helpful

For latest recommended requirements, visit download page of Ubuntu Desktop.

apt-get and other utilities for working with traditional .deb packages do not work to install and upgrade applications on a Snappy Ubuntu Core system. Instead you use the snappy utility. See the Snappy Tour for details.

To summarize a couple examples from the Snappy Tour, to install the Docker application you would run:

sudo snappy install docker

And to install updates, you run sudo snappy update-versions (which corresponds to sudo apt-get update on a normal Ubuntu system), snappy versions to see what's newly available, and sudo snappy update ... to specify packages for updating (put their names in place of ...).

Because Snappy Ubuntu Core doesn't use .deb packages, Ubuntu packages created for regular Ubuntu systems will not work--the relationship between regular Ubuntu systems and Snappy Ubuntu Core when it comes to package files is, in effect, the same as the relationship between any two distributions that use totally different package managers. (For example: Ubuntu and Fedora.)

Like in just about any OS, you could manually install programs on Snappy Ubuntu Core provided you have or can obtain all the libraries (and any other dependencies) they need. However, just as the best way to install most software on regular Ubuntu systems is with a .deb package, the best way to install software on Snappy Ubuntu Core is with specially built snappy packages. Only a handful of these exist so far.

To search for Snappy Ubuntu Core apps from within a Snappy Ubuntu Core system, use:

snappy search search-term

This finds Snappy packages with search-term in their names. (You'd replace that with whatever you're looking for, of course.)

As for Raspberry Pi, those have ARM processors, which you're right are not the same as the usual 32-bit and 64-bit Intel and AMD processors most of us use on our traditional PCs. However, Raspberry Pi support does not appear to be the main point of Snappy Ubuntu Core. Instead, as you may be aware, the general aim of Snappy is for better speed, stability, and security, in circumstances where a minimal Ubuntu Core system is sufficient and appropriate.

Snappy is cloud-oriented ("Snappy Ubuntu Core is the perfect system for large-scale cloud container deployments..."), and explicitly supports many x86 (i.e., not ARM) platforms--see the list of options under "Try the new, snappy Ubuntu yourself!" on the Snappy home page.

Nonetheless, depending on your needs, Snappy Ubuntu Core may be a reasonable way to get a working Ubuntu Core system on a Raspberry Pi. Depending on which Raspberry Pi board you have, it may or may not support a fuller, more traditional installation of Ubuntu. Note, though, that there are other options that may be more Ubuntu-like in the ways that matter to most users of traditional Ubuntu systems:

• Debian is quite similar to Ubuntu, and provides an experience in many ways more similar to most Ubuntu installations. In particular, like a normal Ubuntu system Debian uses apt-get. In fact apt-get originated in Debian. (Ubuntu is a derivative of Debian.)
• Raspbian is a derivative of Debian made specially for the Raspberry Pi. Like Debian and normal (non-Snappy) Ubuntu systems, uses APT-based package management (i.e., with apt-get). The Debian project's page about Debian on Raspberry Pi even says, "Generally, your best bet is to use Raspbian".

See also this list of operating systems for Raspberry Pi.