This is the "inst" distribution of TeX Live (http://tug.org/texlive).

Normally, you should download the "live" distribution from your nearest
CTAN mirror (CTAN:systems/texlive/Images).  The only reason to use
"inst" is when
(a) you need to burn your own physical cd, *AND*
(b) you are on i386-linux, powerpc-darwin, or win32.

See the TeX Live web pages and documentation for more information.

Please consider joining a TeX user group (e.g., http://tug.org/join.html)
to support this effort (and get the entire TeX Collection on DVD).

(By the way, the .iso is not compressed because the data included is
already compressed; the minor gain in space from further compression is
not worth the loss in time and trouble.)