Puppy Linux has been built from the ground up but can be rebuilt, "based" on other distros using a special script tool "woof".Puppy GNU/Linux is very small - typically about 120MB.
Puppy is designed to be loaded entirely into RAM and ran from there.Puppy is designed to take up a certain percentage of ram, so it typically doesn't load that entire size, so you can run puppy on a machine with very little ram.
Puppy is designed to run entirely out of memory, so it will typically load itself into RAM when you boot, this usually means a slower boot time but it will mean accessing your files and programs will be considerably quicker as they are being accessed via RAM.
This also means you can run puppy on a machine that does not have a hard drive.
Puppy is actually designed to run live, so it is actually not recommended to install it at all. It can be ran from a CD or a USB and can save back to either format (even CD-R). If you do wish to install it to the HDD there is a graphical script you can use called "Puppy Universal Installer.
Puppy can also be built to be compatible with any other packages, currently the "main" puppys are:
- Lucid: based on Ubuntu
- Slacko: based on Slackware
- Wary: built from the ground up to be as compatible as possible with all hardware
- Racy: built from the ground up, using the latest Linux kernel to work best with the latest hardware
