The 2.5" HD drives in laptops uses a finepitch ATA connector with 44 pins instead of 40. The extra 4 pins are for the power to the drive. There exists converters so the drives can be connected to the ordinary sized 40 pins ATA connectors. Note, however, some laptops do not use the 44 pin ATA connector for the CDROM, so make sure that yours does before you purchase the adaptor.