Dual-channel architecture
Encyclopedia
Multi-channel architecture is a technology that increases the transfer speed of data between the RAM
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. Higher-end chipsets like the Intel i7-9x series and various Xeon chipsets support triple-channel memory. Intel is currently (2011) working to develop chipsets that support quad-channel memory. The chipset in the AlphaStation
600 supported 8-channel memory, but the backplane
currently (as of 1995) limits the machine to 4 channels.
(DDR), in which each memory module is accessed twice per clock. The two technologies are independent of each other and many motherboards use both, by using DDR memory in a dual channel configuration.
, DDR2 SDRAM
, or DDR3 SDRAM
memory modules. The memory modules are installed into matching banks, which are usually color coded on the motherboard
. These separate channels allow each memory module access to the memory controller, increasing throughput bandwidth. It is not required that identical modules be used, but this is often recommended for best dual-channel operation. It is possible to use a single-sided module of 512 MB
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.
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:
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.
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.
Tom's Hardware found little significant difference between single-channel and dual-channel configurations in synthetic and gaming benchmarks (using a "modern" system setup). In its tests, dual channel gave at best a 5% speed increase in memory-intensive tasks. Another comparison by laptoplogic.com resulted in a similar conclusion for integrated graphics. The test results published by Tom's Hardware had a discrete graphics comparison.
The difference can be far more significant in applications that manipulate large amounts of data in memory. A comparison by TechConnect Magazine demonstrated considerable gains for dual-channel in tasks using block sizes
greater than 4 MB, and during stream processing
by the CPU.
). 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, 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.
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
mode.
Intel Xeon:
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...
and the memory controller
Memory controller
The memory controller is a digital circuit which manages the flow of data going to and from the main memory. It can be a separate chip or integrated into another chip, such as on the die of a microprocessor...
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. Higher-end chipsets like the Intel i7-9x series and various Xeon chipsets support triple-channel memory. Intel is currently (2011) working to develop chipsets that support quad-channel memory. The chipset in the AlphaStation
AlphaStation
AlphaStation was the name given to a series of computer workstations, produced from 1994 onwards by Digital Equipment Corporation, and latterly by Compaq and HP. As the name suggests, the AlphaStations were based on the DEC Alpha 64-bit microprocessor...
600 supported 8-channel memory, but the backplane
Backplane
A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...
currently (as of 1995) limits the machine to 4 channels.
Dual-channel architecture
Dual-channel-enabled memory controllers utilize two 64-bit data channels. Dual channel should not be confused with double data rateDouble data rate
In computing, a computer bus operating with double data rate transfers data on both the rising and falling edges of the clock signal. This is also known as double pumped, dual-pumped, and double transition....
(DDR), in which each memory module is accessed twice per 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 architecture requires a dual-channel-capable motherboard and two or more DDRDDR SDRAM
Double data rate synchronous dynamic random access memory is a class of memory integrated circuits used in computers. DDR SDRAM has been superseded by DDR2 SDRAM and DDR3 SDRAM, neither of which are either forward or backward compatible with DDR SDRAM, meaning that DDR2 or DDR3 memory modules...
, DDR2 SDRAM
DDR2 SDRAM
DDR2 SDRAM is a double data rate synchronous dynamic random-access memory interface. It supersedes the original DDR SDRAM specification and has itself been superseded by DDR3 SDRAM...
, or DDR3 SDRAM
DDR3 SDRAM
In computing, DDR3 SDRAM, an abbreviation for double data rate type three synchronous dynamic random access memory, is a modern kind of dynamic random access memory with a high bandwidth interface. It is one of several variants of DRAM and associated interface techniques used since the early 1970s...
memory modules. The memory modules are installed into matching banks, which are usually color coded on the motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...
. These separate channels allow each memory module access to the memory controller, increasing throughput bandwidth. It is not required that identical modules be used, but this is often recommended for best dual-channel operation. It is possible to use a single-sided module of 512 MB
Megabyte
The megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
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
DIMM
A DIMM or dual in-line memory module, comprises a series of dynamic random-access memory integrated circuits. These modules are mounted on a printed circuit board and designed for use in personal computers, workstations and servers...
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
Gigabyte
The gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
memory modules in bank 0 and a pair of matched 512 MB modules in bank 1 would be acceptable for dual-channel operation.
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.
- 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. 2 sides with 4 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" system setup). In its tests, dual channel gave at best a 5% speed increase in memory-intensive tasks. Another comparison by laptoplogic.com resulted in a similar conclusion for integrated graphics. The test results published by Tom's Hardware had a discrete graphics comparison.
The difference can be far more significant in applications that manipulate large amounts of data in memory. A comparison by TechConnect Magazine demonstrated considerable gains for dual-channel in tasks using block sizes
Memory pool
Memory pools, also called fixed-size-blocks allocation, allow dynamic memory allocation comparable to malloc or C++'s operator new. As those implementations suffer from fragmentation because of variable block sizes, it can be impossible to use them in a real time system due to performance...
greater than 4 MB, and during stream processing
Stream processing
Stream processing is a computer programming paradigm, related to SIMD , that allows some applications to more easily exploit a limited form of parallel processing...
by the CPU.
Ganged vs 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.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), and the LGA 1366 platform (e.g., Intel X58Intel X58
The Intel X58 is an Intel chip designed to connect Intel processors with Intel QuickPath Interconnect interface to peripheral devices. Supported processors implement the Nehalem microarchitecture and therefore have an integrated memory controller , so the X58 does not have a memory interface...
). AMD Socket AM3
Socket AM3
Socket AM3 is a CPU socket for AMD processors. AM3 was launched as the successor to Socket AM2+ on February 9, 2009, alongside the initial grouping of Phenom II processors designed for it...
processors do not use the DDR3 triple-channel architecture but instead use dual-channel DDR3 memory. The same applies to the Intel Core i3, Core i5 and Core i7-800 series, which are used on the LGA 1156
LGA 1156
LGA 1156, also known as Socket H or H1, is an Intel desktop CPU socket. LGA stands for land grid array. Its incompatible successor is LGA 1155....
platforms (e.g., Intel P55
Intel P55
The Intel P55 is the first desktop chipset from Intel based on the PCH chipset design. The P55 Express chipset uses the LGA 1156 socket. Compatible CPUs include the Core i3, i5, and i7 processor line along with a Pentium Processor G6950...
). 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
Interleaving
In computer science and telecommunication, interleaving is a way to arrange data in a non-contiguous way to increase performance.It is typically used:* In error-correction coding, particularly within data transmission, disk storage, and computer memory....
mode. This, Intel claims, leads to faster system performance as well as higher performance per watt.
When operating in triple-channel mode, memory latency is reduced due to interleaving
Interleaving
In computer science and telecommunication, interleaving is a way to arrange data in a non-contiguous way to increase performance.It is typically used:* In error-correction coding, particularly within data transmission, disk storage, and computer memory....
, 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
Dual-channel architecture
Multi-channel architecture is a technology that increases the transfer speed of data between the RAM 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...
mode.
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