These are 184 pin ddr, they would not have been in the same computer from the manufacturer as they are different speeds, however, they will work together in a computer but if the computer is able to run the mamory in dual channel mode, it will not run in dual channel mode (128 Bit Transfer rate) with mismatched speeds of ram, it will default to single mode (64 Bit Transfer Rate) and both sticks will run only as fast as the slowest stick, in this case 266MHZ (PC2100)