Capacity: 256GB (2x128GB) --- Technology: DDR4 --- Speed: PC4-21300 2666MHz CL19 --- ECC Type: ECC Registered --- Form Factor: 288-Pin ECC DIMM (RDIMM) --- Voltage: 1.2V --- Backward Compatibility: Also compatible with 2400MHz and 2133MHz --- OWC DDR4 memory is Fully compliant with JEDEC specifications, ROHS compliant, providing a warranty safe upgrade. OWC Memory is the most cost effective and simple DIY upgrade you can install to unleash your Mac or PC's full potential and speed up overall responsiveness. Become a multitasking maven when you upgrade your Mac or PC with OWC Memory. Open more apps. Open larger files. Plus, work with multiple files all at the same time. We test every OWC memory module at our in house lab so you can upgrade with the confidence that your memory is built to last. We built your OWC Memory upgrade to meet or exceed the toughest industry specs to provide years of worry-free service. OWC recommends that all DIMMs be the same capacity, speed, and manufacturer to ensure optimal memory performance.