BackTrack is a Linux-based penetration testing arsenal that aids security professionals in the ability to perform assessments in a purely native environment dedicated to hacking. BackTrack has been customized down to every package, kernel configuration, script and patch solely for the purpose of the penetration tester. This release contains over 120 bug fixes, 30 new tools and 70 tool updates. The kernel was updated to 2.6.39.4 and includes the relevant injection patches. Backtrack 5 R1 contains Gnome and KDE ISO images for 32 and 64 bit (no arm this release)
Source: https://thehackernews.com/2011/08/backtrack-5-r1-released-download-now.html