When comparing Puppy Linux vs Ubuntu LTS, the Slant community recommends Puppy Linux for most people. In the question“What are the best Linux distributions for misanthropes?” Puppy Linux is ranked 14th while Ubuntu LTS is ranked 100th. The most important reason people chose Puppy Linux is:
Puppy Linux requires 128MB of RAM and 333Mhz of CPU, although 256MB of RAM is recommended.
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Pros
Pro Extremely low minimum system requirements
Puppy Linux requires 128MB of RAM and 333Mhz of CPU, although 256MB of RAM is recommended.
Pro The whole OS runs off of RAM
Since Puppy Linux is completely loaded and run off of RAM instead of HDD, it's read/write speed is not a factor.
Pro Designed to run as a live USB/CD
A portable version, that can be carried on a thumb drive without requiring installation, weighs less than 100MB; a Live CD - less than 150MB. You can even save your settings and files for Puppy on the external device/media.
Running off a live CD also has security benefits, as your system will reset to the known config after each boot.
Pro Different distro based versions available
Puppy Linux offers a few different releases.
The first is an Ubuntu based release called Tahrpup, by using this version the user is able to take advantage of all software and support from Ubuntu.
The second version is called Slacko, which is built upon the Slackware binaries.
The third is called Wary and it is built to support older hardware than the rest.
And the fourth is called Quirky, which is used as a base to explore new ideas.
Pro Linux distro designed for this exact purpose
Pro Offers a long term support release
Puppy Linux offers an LTS release called Precise.
Pro It can be the only distro that works
Sometimes, Puppy Linux is the only distro that works on an old machine: all other distros are more demanding.
Pro JWM used as window manager
JWM is a low resource window manager that is used in most Puppy Linux installs.
Pro Just works out of the box
Lots of support for hardware, lots of pre-installed software, and a smooth install process means less time downloading drivers, less time digging through configuration files, and less time deciding on software to use just to get up and running. It also means less time digging through forums looking for support.
Pro Good PPA repositories available
PPA repositories allow you to install the latest version of your preferred software while keeping the rest of the operating system "stable".
Pro Great Long Term Support release schedule (2 years)
This allows for users to always have a new supported release available without long unkown wait times in between.
Pro Lots of support
As the most popular Linux distribution, there's a wide range of sources for support online if you ever need help, including the Ubuntu Wiki, Ubuntu Forums and the Ask Ubuntu Stack Exchange site.
Pro Most users are already familiar with it
Ubuntu is the go-to Linux distro for most people, so there is a sense of familiarity and comfort in using something they have used before.
Cons
Con A bit ugly
Using puppy makes you feel like you just jumped 20 years into the past. Being that the purpose of Puppy Linux is to run or really low resource machines the software used is often on the older side, which is precisely why it has a 20 year old look.
Con Not as light as it used to be
It's light, but not as light as it was 1-2 years ago.
Con Smallest software library ever
You can barely find any precompiled packages for Puppy.
Con No built in compositing
Being a low resource distro there is zero built in compositing for the JWM window manager. Though one can be added through a bit of work.
Con Relatively high system requirements
The default Unity desktop environment is a resource hog which requires hardware accelerated graphics rendering in order to run smoothly, making out of the box Ubuntu unsuitable for low end systems and older hardware. Even mildly aged hardware, you'll get far better performance out of a lighter desktop environment like LXDE or XFCE.