A minimal install of PC-BSD 1.x usually consomes about 3~5gb last I checked, as point in fact. My test machine had about an 8.4gb disk drive that was half full running PC-BSD 1.0RC1 w/o adding files.
PC-BSD7 will probably be the same or larger :\. If the low end hardware is important and small disk drives
, you should try one of the regular BSDS (Free,Net, or Open), something like DSL
might be of interest to you.
It's important to note though, for an upgrade between versions, e.g. 1.5->1.5.1, enough disk space on / is typically
required. This can be from a few tens of megs to a couple of gigs [b]free space[b], and can be quit damaging to stability if a large upgrade fails to upgrade proper because of it.
FreeBSDs file system also keeps a reserve of 8% free space for performance reasons (among other ones), and will degrade if there is less then 15% free space.
I'd say that you could cram FreeBSD or OpenBSD into a 2GB disk drive easy enough, it's just a Q of how much you'd want. If I had that kind of disk space, I'd do a custom install of FreeBSD... Which allows one to strip things down a bit more.