PS2 back ups with out mod ? possible ?

[charlie_ps2]

There is a mechanical method using a knife shoved into the guts of the PS2 to force a tray swap; this is used in conjunction with a boot disk like Action Replay 2.

There is also the mod (in a different sense from what you probably meant) - this is a flip-top cover that replaces the PS2 case top. Works better than shoving a knife in but the method has playing/booting limitations.