The heat from the computer provides a natural growth and germination mechanism for an aspiring botanist. However, water is clearly involved here and we all know that water and technology do not mix. That's why Mike used an old computer someone had given him to test his theory. The radiant heat from a computer could create an ideal soil bed for plants, but just placing a planter on top of the computer wouldn't provide enough contact with the heat source.
Once it was built, the other main challenge was getting the temperature right. Mike says: "Using the fans to control the case temperature allowed me to vary the temperature inside the case from a low of 75°F (24°C) to a high of 91°F (33°C). In order to achieve the desired increase in soil temperature, I had to run the case temperature toward the higher end of the scale."
In case you're curious about the plant: it's wheat grass, which needs plenty of heat to grow and took well to Mike's new planter. You can see the full explanation of his project on his blog, Total Geekdom.
(Image: Total Geekdom)