What is "mcdram"

Multi-Channel DRAM or MCDRAM (pronounced em cee dee ram) is a 3D-stacked DRAM that is used in the Intel Xeon Phi processor codenamed Knights Landing. It is a version of High Bandwidth Memory and a competitor to Hybrid Memory Cube.

The many cores in the Xeon Phi processors, along with their associated vector processing units, enable them to consume many more gigabytes per second than traditional DRAM DIMMs can supply. The "Multi-channel" part of the MCDRAM full name reflects the cores having many more channels available to access the MCDRAM than processors have to access their attached DIMMs. This high channel count leads to MCDRAM's high bandwidth, up to 400+ GB/s, although the latencies are similar to a DIMM access.

Its physical placement on the processor imposes some limits on capacity - up to 16GB at launch, although speculated to go higher in the future.