Slackware is modular and light. No heavy hardware needed to run fully functioning linux box.

Slackware is simple, flexible and extremely customizable. Slackware encourages Linux-way attitude and KISS principle. It does not require high end hardware and can be installed in very restrictive environments. Slackware is very stable and gives the user full control. Most packages are available in "slackbuild" form - the programs can be installed by compiling in place, thus providing the best compatibility with the system. It is very light on system resources. A minimalistic setup can run on very old hardware, so there is no need of constantly upgrading the workstation. This is probably the only Linux distribution that can be run straight out of the box. The uptime is measured in years and only limited by hardware endurance. The installation is very fast, usually it takes only 10-15 minutes in order to have a fully working system.

I have been using Slackware since 1999. It runs extremely well on older hardware due to Pat's iron fist hold on the distribution. GCC compiles fas, the packages are from the "stable" branch and everything is thoroughly tested before release.