Multi-Channel DRAM or MCDRAM (pronounced ''em cee dee ram'') is a
3D-stacked DRAM
Dynamic random-access memory (dynamic RAM or DRAM) is a type of random-access semiconductor memory that stores each bit of data in a memory cell, usually consisting of a tiny capacitor and a transistor, both typically based on metal-oxi ...
that is used in the
Intel
Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, Santa Clara, California. It is the world's largest semiconductor chip manufacturer by revenue, and is one of the devel ...
Xeon Phi
Xeon Phi was a series of x86 manycore processors designed and made by Intel. It was intended for use in supercomputers, servers, and high-end workstations. Its architecture allowed use of standard programming languages and application progra ...
processor codenamed
Knights Landing
Knights Landing (formerly, Baltimore and East Grafton) is a census-designated place in Yolo County, California, United States, founded by William Knight. It is located on the Sacramento River around 25 miles northwest of Sacramento in the northeas ...
. It is a version of
Hybrid Memory Cube
Hybrid Memory Cube (HMC) is a high-performance computer random-access memory (RAM) interface for through-silicon vias (TSV)-based stacked DRAM memory competing with the incompatible rival interface High Bandwidth Memory (HBM).
Overview
Hybrid M ...
developed in partnership with
Micron Technology
Micron Technology, Inc. is an American producer of computer memory and computer data storage including dynamic random-access memory, flash memory, and USB flash drives. It is headquartered in Boise, Idaho. Its consumer products, including ...
, and a competitor to
High Bandwidth Memory
High Bandwidth Memory (HBM) is a high-speed computer memory interface for 3D-stacked synchronous dynamic random-access memory (SDRAM) initially from Samsung, AMD and SK Hynix. It is used in conjunction with high-performance graphics accelerator ...
.
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 16 GB at launch, although speculated to go higher in the future.
Programming
The memory can be partitioned at boot time, with some used as cache for more distant DDR, and the remainder mapped into the physical address space.
The application can request pages of
virtual memory
In computing, virtual memory, or virtual storage is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a very ...
to be assigned to either the distant DDR directly, to the portion of DDR that is cached by the MCDRAM, or to the portion of the MCDRAM that is not being used as cache. One way to do this is via the
memkind API.
When used as cache, the latency of a miss accessing both the MCDRAM and DDR is slightly higher than going directly to DDR, and so applications may need to be tuned
to avoid excessive cache misses.
References
External links
MCDRAM (High Bandwidth Memory) on Knights Landing – Analysis Methods & ToolsAn Intro to MCDRAM (High Bandwidth Memory) on Knights LandingHigh Bandwidth Memory (HBM): how will it benefit your application?Micron HMC Webinar July 2017 slides{{Intel processors
Computer architecture
Intel
Intel microprocessors
Parallel computing
X86 microprocessors
Computer memory