The product is a set of four Hynix 1GB 1Rx8 PC2-6400U-666-12 DDR2 SDRAM RAM modules, totaling 4GB of memory. Each module has a capacity of 1GB and a bus speed of PC2-6400 (DDR2-800). The form factor of these RAM modules is DIMM, making them suitable for standard desktop computer setups. With the Hynix brand reputation known for producing reliable memory modules, this product is an ideal choice for upgrading or replacing existing RAM in systems requiring DDR2 memory technology.