Multi-channel memory architecture
1
Multi-channel memory architecture
Multi-channel memory architecture is a technology that increases the transfer speed of data between the DRAM
and the memory controller by adding more channels of communication between them. Theoretically this multiplies
the data rate by exactly the number of channels present. Dual-channel memory employs two channels which
theoretically doubles the data transfer rate. The technique goes back as far as the 1960s having been used in IBM
System/360 Model 91 and in CDC 6600.[1]
Modern higher-end chipsets like the Intel i7-9x series and various Xeon chipsets support triple-channel memory. On
March, 2010 AMD released Socket G34 and Magny-Cours Opteron 6100 series[2] processors which support
quad-channel memory. In 2011 Intel released chipsets that support quad-channel memory for their LGA2011
platform.[3] Historically, microcomputer chipsets with even more channels had been designed. For example, the
chipset in the AlphaStation 600 (1995) supported eight-channel memory, but the backplane of the machine limited
operation to four channels.[4]
Dual-channel architecture
Dual-channel-enabled memory controllers in a PC system architecture
utilize two 64-bit data channels. Dual channel should not be confused
with double data rate (DDR), in which data exchange happens twice
per DRAM clock. The two technologies are independent of each other
and many motherboards use both, by using DDR memory in a
dual-channel configuration.
Operation
Dual channel memory slots, orange and yellow
Dual-channel
architecture
requires
a
dual-channel-capable
for each channel. Paired memory chips should go
motherboard and two or more DDR, DDR2 SDRAM, or DDR3
in slots of same color.
SDRAM memory modules. The memory modules are installed into
matching banks, which are usually color-coded on the motherboard. These separate channels allow the memory
controller access to each memory module, increasing throughput bandwidth. It is not required that identical modules
be used (if motherboard supports it), but this is often recommended for best dual-channel operation. It is possible to
use a single-sided module of 512 MB[5] and a double-sided module of 512 MB in dual-channel configuration, but
how fast and stable it is depends on the memory controller.
If the motherboard has two pairs of differently colored DIMM sockets (the colors indicate which bank they belong
to, bank 0 or bank 1), then one can place a matched pair of memory modules in bank 0, but a different-capacity pair
of modules in bank 1, as long as they are of the same speed. Using this scheme, a pair of 1 GB memory modules in
bank 0 and a pair of matched 512 MB modules in bank 1 would be acceptable for dual-channel operation.[6]
Modules rated at different speeds can be run in dual-channel mode, although the motherboard will then run all
memory modules at the speed of the slowest module. Some motherboards, however, have compatibility issues with
certain brands or models of memory when attempting to use them in dual-channel mode. For this reason, it is
generally advised to use identical pairs of memory modules, which is why most memory manufacturers now sell
"kits" of matched-pair DIMMs. Several motherboard manufacturers only support configurations where a "matched
pair" of modules are used. A matching pair needs to match in:
• Capacity (e.g. 1024 MB). Certain Intel chipsets support different capacity chips in what they call Flex Mode: the
capacity that can be matched is run in dual-channel, while the remainder runs in single-channel.
Multi-channel memory architecture
• Speed (e.g. PC5300). If speed is not the same, the lower speed of the two modules will be used. Likewise, the
higher latency of the two modules will be used.
• Number of chips and sides (e.g. two sides with four chips on each side).
• Matching size of rows and columns.
Dual-channel architecture is a technology implemented on motherboards by the motherboard manufacturer and does
not apply to memory modules. Theoretically any matched pair of memory modules may be used in either single- or
dual-channel operation, provided the motherboard supports this architecture.
Purpose
Dual-channel technology was created to address the issue of bottlenecks. Increased processor speed and performance
requires other, less prominent components to keep pace. In the case of dual-channel design, the intended target is the
memory controller, which regulates data flow between the CPU and system memory (RAM). The memory controller
determines the types and speeds of RAM as well as the maximum size of each individual memory module and the
overall memory capacity of the system. However, when the memory is unable to keep up with the processor, a
bottleneck occurs, leaving the CPU with nothing to process. Under the single-channel architecture, any CPU with a
bus speed greater than the memory speed would be susceptible to this bottleneck effect.
The dual-channel configuration alleviates the problem by doubling the amount of available memory bandwidth.
Instead of a single memory channel, a second parallel channel is added. With two channels working simultaneously,
the bottleneck is reduced. Rather than wait for memory technology to improve, dual-channel architecture simply
takes the existing RAM technology and improves the method in which it is handled. While the actual
implementation differs between Intel and AMD motherboards, the basic theory stands.
Performance
There have been varying reports as to the performance increase of dual-channel configurations, with some tests
citing significant performance gains while others suggest almost no gain.
Tom's Hardware found little significant difference between single-channel and dual-channel configurations in
synthetic and gaming benchmarks (using a "modern (2007)" system setup). In its tests, dual channel gave at best a
5% speed increase in memory-intensive tasks.[7] Another comparison by laptoplogic.com resulted in a similar
conclusion for integrated graphics.[8] The test results published by Tom's Hardware had a discrete graphics
comparison.
Ganged versus unganged
Dual-channel was originally conceived as a way to maximize memory throughput by combining two 64-bit buses
into a single 128-bit bus. This is retrospectively called the "ganged" mode. However, due to lackluster performance
gains in consumer applications as discussed above, more modern implementations of dual-channel use the
"unganged" mode by default, which maintains two 64-bit memory buses but allows independent access to each
channel, in support of multithreading with multi-core processors.
Triple-channel architecture
Operation
DDR3 triple-channel architecture is used in the Intel Core i7-900 series (the Intel Core i7-800 series only support up
to dual-channel). The LGA 1366 platform (e.g. Intel X58) supports DDR3 triple-channel, normally 1333 and
1600Mhz, but can run at higher clock speeds on certain motherboards. AMD Socket AM3 processors do not use the
DDR3 triple-channel architecture but instead use dual-channel DDR3 memory. The same applies to the Intel Core i3,
2
Multi-channel memory architecture
Core i5 and Core i7-800 series, which are used on the LGA 1156 platforms (e.g., Intel P55). According to Intel, a
Core i7 with DDR3 operating at 1066 MHz will offer peak data transfer rates of 25.6 GB/s when operating in
triple-channel interleaved mode. This, Intel claims, leads to faster system performance as well as higher performance
per watt.[9]
When operating in triple-channel mode, memory latency is reduced due to interleaving, meaning that each module is
accessed sequentially for smaller bits of data rather than completely filling up one module before accessing the next
one. Data is spread amongst the modules in an alternating pattern, potentially tripling available memory bandwidth
for the same amount of data, as opposed to storing it all on one module.
The architecture can only be used when all three, or a multiple of three, memory modules are identical in capacity
and speed, and are placed in three-channel slots. When two memory modules are installed, the architecture will
operate in dual-channel architecture mode.[10]
Supporting processors
Intel Core i7:
• Intel Core i7-9xx Bloomfield, Gulftown
• Intel Core i7-9x0X Gulftown
Intel Xeon:
•
•
•
•
•
•
•
•
•
•
•
Intel Xeon E55xx Nehalem-EP
Intel Xeon E56xx Westmere-EP
Intel Xeon ECxxxx Jasper Forest
Intel Xeon L55xx Nehalem-EP
Intel Xeon L5609 Westmere-EP
Intel Xeon L5630 Westmere-EP
Intel Xeon L5640 Westmere-EP
Intel Xeon LC55x8 Jasper Forest
Intel Xeon Wxxxx Bloomfield, Nehalem-EP, Westmere-EP
Intel Xeon X55xx Nehalem-EP
Intel Xeon X56xx Westmere-EP[11][12]
Quadruple-channel architecture
Operation
DDR3 Quadruple-channel architecture is used in the AMD G34 platform and the Intel LGA 2011 platform (e.g.,
Intel X79). AMD processors which are used on the C32 platform instead use dual-channel DDR3 memory. Intel
processors which are used on the LGA 1155 platform (e.g., Intel Z68) instead use dual-channel DDR3 memory.
The architecture can only be used when all four, or a multiple of four, memory modules are identical in capacity and
speed, and are placed in quad-channel slots. When two memory modules are installed, the architecture will operate
in dual-channel architecture mode. When three memory modules are installed, the architecture will operate in
triple-channel architecture mode.[10]
3
Multi-channel memory architecture
4
Supporting processors
AMD Opteron:
• Opteron 6100-series "Magny-Cours" (45 nm)[2]
• Opteron 6200-series "Interlagos" (32 nm)[13]
Intel Core i7:
•
•
•
•
Intel Core i7-3970X
Intel Core i7-3960X
Intel Core i7-3930K
Intel Core i7-3820
Intel Xeon:
• Intel Xeon E5-16xx
• Intel Xeon E5-26xx
References
[1] Bruce Jacob; Spencer Ng; David Wang (2007). Memory systems: cache, DRAM, disk. Morgan Kaufmann. p. 318. ISBN 978-0-12-379751-3.
[2] "AMD Opteron 6000 Series Platform Quick Reference Guide" (http:/ / sites. amd. com/ us/ documents/ 48101a_opteron _6000_qrg_rd2. pdf).
. Retrieved 2012-10-15.
[3] http:/ / www. techpowerup. com/ 138087/ Intel-LGA2011-Socket-X68-Express-Chipset-Pictured. html
[4] http:/ / www. hpl. hp. com/ hpjournal/ dtj/ vol7num1/ vol7num1art7. txt
[5] RAM size is specified using binary meanings for K (10241 instead of 10001), M (10242 instead of 10002), G (10243 instead of 10003), ...
[6] Infineon Technologies North America Corporation and Kingston Technology Company, Inc. (September 2003). ""Intel Dual-Channel DDR
Memory Architecture White Paper", Rev. 1.0" (http:/ / www. kingston. com/ newtech/ MKF_520DDRwhitepaper. pdf) (PDF, 1021 KB).
Kingston Technology. . Retrieved 2007-09-06.
[7] Parallel Processing, Part 2: RAM and HDD | Tom's Hardware (http:/ / www. tomshardware. com/ reviews/
PARALLEL-PROCESSING,1705-15. html)
[8] Intel's Sonoma Platform: Dual Channel Performance (http:/ / laptoplogic. com/ resources/ detail. php?id=20)
[9] Intel X58 Product Brief (http:/ / www. intel. com/ Assets/ PDF/ prodbrief/ x58-product-brief. pdf),
[10] Desktop Boards - Triple Memory Modules (http:/ / support. intel. com/ support/ motherboards/ desktop/ sb/ CS-011965. htm#triple),
[11] Intel, ed. "Intel Core i7 Family Product Comparison" (http:/ / ark. intel. com/ Compare.
aspx?ids=48139,43559,43560,43562,43563,49666,47700,49654,50022,49158,49664,43122,49024,43124,43125,54616,52231,54610,52219,53463,54611,54615,53
Memory Specifications: # of Memory Channels. .
[12] Intel, ed. "Intel Xeon Family Product Comparison" (http:/ / ark. intel. com/ Compare.
aspx?ids=49942,49943,49944,49945,49946,27076,33103,27077,27078,27099,27080,28014,28015,27100,27093,27094,27101,28016,28017,27083,27084,27102,27
Memory Specifications: # of Memory Channels. .
[13] "AMD Opteron 6200 Series Processor Quick Reference Guide" (http:/ / www. amd. com/ us/ Documents/ Opteron_6000_QRG. pdf). .
Retrieved 2012-10-15.
External links
• Single, dual, triple and flex memory modes (http://www.intel.com/support/motherboards/desktop/sb/
cs-011965.htm)
Article Sources and Contributors
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