Compatability of DDR,DDR2,DDR3?

ddr/2/3 are backwards compatible only, as you read. are you sure yuo dont mean you found a ddr stick in a ddr2 slot? that would work. however, if by some bizarre twist you found a ddr2 card inside a ddr slot, it is possible, though extremely unlikly, that it fit in the slot, but was not actually functioning. if this were the case the computer would be working with the other card/s in the chip or on the motherboards built in backup ram (usually 32mb)