Upgrade the memory in your compatible Mac using the 16GB DDR3L 1866 MHz SO-DIMM Memory Kit from Crucial. This memory kit features a total capacity of 16GB, which is made of up two 8GB modules. It also has a clock speed of 1866 MHz, a bus speed of PC3-14900, and a 204-pin SO-DIMM form factor. It operates using 1.35V, has a CAS latency of 13, does not use ECC technology, and is unbuffered. This RAM is compatible with the 27" iMac with Retina 5K (late 2015) and is protected by a limited lifetime warranty.