The Micron PC2100S 256 MB SO-DIMM 266 MHz DDR memory module is a single module with a form factor of SO-DIMM and 200 pins. It has a bus speed of PC-2100 (DDR-266) and is designed for high performance in computers and laptops. While the product has not been tested, it is a reliable option for upgrading or replacing memory modules in systems that require DDR memory. The Micron brand ensures quality and compatibility with a variety of devices.