The Greenphone SDK installs to your hardrive and can get quite large as you compile and use it.
It needs a fairly fast computer, as it runs as a virtual machine.
Greenphone SDK minimum requirements:
Windows® 2000, Windows XP or GNU/Linux Operating Systems
512 MB RAM
For version 4.2.1 and greater, the Greenphone SDK can take up to 10 Gb HDD space, with a minimum of 3 Gb required
1 GHz CPU