More boxen is a slang term in computing expressing a need for more computing power. A "box" refers to the main processing hardware of the computer, which is normally installed in a metal case, or box.
Boxen is the deliberately corrupted plural form of box, following the "ox" -> "oxen" rule. The image of a herd of oxen is appropriate when talking about the technique of interconnecting computers in "clusters" of dozens or hundreds.
You can say it when you need more computers or when you want to upgrade your computer.
It is used among distributed computing fans who connect several small computers together to build personal supercomputers.
