The product is a set of four Kingston 4GB DDR3 SDRAM SO-DIMM modules, with a total capacity of 16GB. Two of the modules have a S circled on them. These memory modules are designed for use in computers and laptops, with a bus speed of PC3-12800 (DDR3-1600). Made in the USA, this product is ideal for increasing the memory capacity of your device and improving overall performance. With the trusted brand of Kingston and the high-quality components, this RAM set ensures reliable and efficient operation for your computing needs.