CISO format (.cso) programs

[Flash]

Yeah backups rock, so pack your original untouched isos with 7zip (maximum compression) and store somewhere, like external HDD.

Also it's better to use command line tool because it gives more control and it will be harder to screw things up - cisoplus. Also -rm_update option removes system update, but it never altered anything else - all games were perfectly working without system update, so it's safe and recommended, especially when it comes to real PSP and memory stick space.