Dual channel memory technology

Simple definition

Dual channels are actually two memory controllers. What is a memory controller? If the CPU is like a factory and the memory is like a warehouse, then the memory controller is the warehouse manager. Single-channel means that there is only one door from the factory to the warehouse, and an administrator can only pick up one batch of goods at a time. The dual aisle means that another warehouse is built, another administrator is added, and raw materials are provided to the factory at the same time. The raw materials provided are doubled each time.

If we increase the memory, we will increase the warehouse. The warehouse is large and the stocks are sufficient. The factory does not need to go outside to buy things, and the production speed is naturally fast. There is one more warehouse manager and one more export that provides raw materials to the factory. The speed at which the warehouse provides raw materials to the factory increases, and the factory is naturally faster. This is probably the reason.

Technical support

1) For all Intel CPUs and AMDK7 products of the soket462 architecture, whether they support dual channels, mainly depends on whether the motherboard or CPU has two memory controllers. p>

2) For all AMD K8s and the newly released Sempron 754 architecture, their system memory controller is implemented in the CPU, which means that the organization of the warehouse manager is managed by the CPU, so, Whether this system supports dual channels or not, the CPU has the final say, it has nothing to do with the motherboard. For example, all 754-pin CPUs can only support single-channel, not dual-channel. All 939-pin CPUs support dual channels.

As for the motherboards that support dual channels? Our common Intel chipsets, 848, 865PE (not without E) and above, will support dual channels. For other chipset motherboards such as VIA and SIS, you should check whether it is dual-channel in its product information. If it is the second case above, you only need to consider whether to buy 939 AMD or 754 AMD.

Scientific definition

Dual-channel memory technology is actually a kind of memory control and management technology, which relies on the memory controller of the chipset to function. In theory, it can make two equal The bandwidth provided by the specification memory has doubled. It is not a new technology. It has long been used in server and workstation systems. It only came to the forefront of desktop motherboard technology to solve the increasingly embarrassing memory bandwidth bottleneck problem of desktop computers. A few years ago, Intel introduced the i820 chipset that supports dual-channel memory transfer technology. It forms a golden partner with RDRAM memory. The outstanding performance makes it the biggest highlight of the market for a while, but the production cost The excessively high defect caused a situation of not being popular, and was finally eliminated by the market. Since Intel has given up support for RDRAM, the current dual-channel memory technology of mainstream chipsets refers to dual-channel DDR memory technology. The mainstream dual-channel memory platform Intel is Intel 865/875 series, and AMD is NVIDIA Nforce2 series. .

Solve the problem

Dual-channel memory technology is a low-cost, high-performance solution to the contradiction between CPU bus bandwidth and memory bandwidth. Now the FSB (front side bus frequency) of CPU is getting higher and higher, Intel Pentium4 has much higher demand for memory bandwidth than AMDAthlonXP. The data transmission between the Intel Pentium4 processor and the Northbridge chip uses QDR (QuadDataRate) technology, and its FSB is 4 times the FSB. The FSB of Intel Pentium4 is 400/533/800MHz, the bus bandwidth is 3.2GB/sec, 4.2GB/sec and 6.4GB/sec, while the memory bandwidth provided by DDR266/DDR333/DDR400 is 2.1GB/sec, 2.7GB/sec and 3.2GB/sec. In the single-channel memory mode, DDR memory cannot provide the data bandwidth required by the CPU and thus becomes the performance bottleneck of the system. In dual-channel memory mode, the memory bandwidths provided by dual-channel DDR266/DDR333/DDR400 are 4.2GB/sec, 5.4GB/sec and 6.4GB/sec respectively. As you can see here, dual-channel DDR400 memory is just fine. Meet the bandwidth requirement of 800MHz FSBPentium4 processor. For AMDAthlonXP platform, the data transmission technology of its processor and north bridge chip adopts DDR (DoubleDataRate, double data transmission) technology, FSB is twice the FSB, and its demand for memory bandwidth is much lower than that of Intel Pentium4 platform. , Its FSB is 266/333/400MHz, and the bus bandwidth is 2.1GB/sec, 2.7GB/sec and 3.2GB/sec. Single-channel DDR266/DDR333/DDR400 can meet its bandwidth requirements, so on AMDK7 platform The use of dual-channel DDR memory technology is not as effective as the Intel platform. The most obvious impact on performance is the integrated motherboard with integrated display chip.

Related products

NVIDIA's nForce chipset is the first chipset to expand the DDR memory interface to 128-bit, and Intel subsequently introduced its E7500 server motherboard chipset This dual-channel DDR memory technology is also used, and SiS and VIA have responded one after another, actively researching and developing this technology that can double the bandwidth of DDR memory. However, due to various reasons, it is not easy for many chipset manufacturers to realize this dual-channel DDR (128bit parallel memory interface) transmission. DDRSDRAM memory is completely different from RDRAM memory. The latter has high latency characteristics and is a serial transmission method. These characteristics determine that the difficulty and cost of designing a dual-channel RDRAM memory chip set are not too high. However, DDRSDRAM memory has its own limitations. It has low-latency characteristics and uses parallel transmission mode. The most important point is that when the operating frequency of DDRSDRAM is higher than 400MHz, its signal waveform often has distortion problems. All of these have brought great difficulty to design a chipset that supports dual-channel DDR memory systems, and the manufacturing cost of the chipset will increase accordingly. These factors restrict the development of this memory control technology.

A common single-channel memory system has a 64-bit memory controller, while a dual-channel memory system has two 64-bit memory controllers, which have a 128-bit memory width in dual-channel mode. So as to theoretically double the memory bandwidth. Although the bandwidth provided by the dual 64-bit memory system is equivalent to the bandwidth provided by a 128-bit memory system, the effects achieved by the two are different. The dual-channel system includes two independent and complementary intelligent memory controllers. In theory, both memory controllers can operate simultaneously with zero delay between each other. For example, there are two memory controllers, one is A and the other is B. When controller B is ready to access the memory for the next time, controller A is reading/writing the main memory, and vice versa. This complementary "nature" of the two memory controllers can reduce the waiting time by 50%. The two memory controllers of dual-channel DDR are completely the same in function, and the timing parameters of the two controllers can be programmed individually. This flexibility allows users to use two DIMM memory modules with different structures, capacities, and speeds. At this time, dual-channel DDR is simply adjusted to the lowest memory standard to achieve 128bit bandwidth, allowing DIMM memory modules with different density/latency characteristics to be Reliably work together.

Desktop chipsets that support dual-channel DDR memory technology. Intel platforms include Intel's 865P/865G/865GV/865PE/875P and later 915/925 series; VIA's PT880, ATI's Radeon9100IGP series , SIS’s SIIS655, SIS655FX and SIS655TX; AMD platform has VIA’s KT880, NVIDIA’s nForce2Ultra400, nForce2IGP, nForce2SPP and later chips.

Principle

With the introduction of the 800MHzP4 front-side bus, the bandwidth requirements of the processor for the memory system are getting higher and higher, and the memory bandwidth has become an increasing bottleneck of the system. Memory manufacturers can increase the bandwidth as long as the operating frequency of the memory is increased. However, due to the constraints of the characteristics of the transistor itself and the manufacturing technology, the memory frequency cannot be increased indefinitely. Therefore, before the development of a new memory, the dual-channel memory technology Become a technology that can effectively increase memory bandwidth. Its biggest advantage is that as long as the memory control method is changed, the memory bandwidth can be improved on the basis of the existing memory. From the perspective of theoretical indicators, dual-channel memory technology has considerable advantages. The theoretical bandwidth of dual-channel DDR400 is 64GB/s, which perfectly matches Intel's P4 processor and i865 and i875 chipsets with an 800MHz front-side bus. The choice of dual-channel DDR400 for the P4 platform with a front-side bus of 800MHz has a lot to do with the dual-channel memory control and management mechanism and high bandwidth.

Dual-channel memory technology is actually dual-channel memory control technology, which can effectively increase the total bandwidth of the memory to meet the needs of data transmission and processing of the new microprocessor. Dual-channel DDR has two 64-bit memory controllers, and the bandwidth provided by the dual 64-bit memory system is equivalent to the bandwidth provided by a 128-bit memory system.

The dual-channel system includes two independent and complementary intelligent memory controllers, both of which can operate in parallel. For example, when controller B is ready to access the memory next time, controller A is reading/writing main memory, and vice versa. This complementary "nature" of the two memory controllers can reduce the effective waiting time by 50%, so the dual-channel technology doubles the bandwidth of the memory. Its technical core lies in: the chipset (North Bridge) can address and read data separately on two different data channels, and the RAM can reach a bandwidth of 128bit.

Development

Dual-channel memory technology originally started with RDRAM memory sticks introduced by RAMBUS. RAMBUS memory speed is very fast, but the bus width is smaller than SDRAM memory, so it has to combine Intel's dual-channel memory control technology to increase bandwidth and achieve the purpose of high-speed data transmission rate. However, RAMBUS was gradually eliminated by the market due to high production costs, but the dual-channel memory control technology has been carried forward. The NetBurst architecture used by Pentium 4 now requires very high memory bandwidth. If the memory cannot provide the corresponding data transfer rate, such a fast processor bus speed is useless.

So only through dual-channel memory control technology can this problem be solved. Jinbang recently launched DDR500 memory modules, with a single data bandwidth of 4GB. If dual-channel technology is used, the bandwidth will reach 8GB.

Application

Dual-channel memory mainly relies on the control technology of the motherboard's north bridge, and has nothing to do with the memory itself. Currently, motherboards supporting dual-channel memory technology include Intel’s i865 and i875 series, SIS’s SIS655 and 658 series, and nVIDIAD’s nFORCE2 series. Intel's first chipsets supporting dual-channel memory technology are the E7205 and E7500 series.

There are certain requirements for the installation of dual-channel memory. The color and layout of the motherboard's memory slots are generally differentiated. If it is Intel's i865 and i875 series, the motherboard generally has 4 DIMM slots, each group of two, each group is generally different in color, each group represents a memory channel, only when both channels are installed at the same time In order to make the memory work in dual channel mode. Also pay attention to symmetrical installation, that is, the first slot of the first channel matches the first slot of the second channel, and so on. Users only need to match different colors and install them in a seated manner.

If you install a memory module in the same color slot, it can only work in single-channel mode. The nFORCE2 series motherboards also have two 64-bit memory controllers, where the A controller only supports one memory slot, and the B channel supports two. There is a distance between the A and B slots to facilitate user identification. The color of the A-channel memory slot may also be different from the two memory slots of the B-channel. Users only need to insert one memory into an independent memory slot and the other into the other two memory slots close to each other. Set up a dual channel mode. In addition, if the memory is fully inserted, dual-channel mode can also be established, and the nForce2 motherboard has no strict requirements on the memory capacity or even the model when it is set up in the dual-channel mode, which is easy to use.

If the installation method is correct, the screen displays the working mode of the memory (such as DDR333DualChannelModeEnabled, activate dual channel mode, etc.) when the motherboard power-on self-test, then the memory is already working in dual channel mode.

There are problems

The emergence of dual-channel memory control technology has improved the performance of users using P4 and is also a future development trend. When assembling a dual-channel memory system, pay attention to the combination of memory modules. Intel’s requirements are higher than other motherboards. It is best to use memory modules of the same brand and model to ensure stability.

Any technology has its advantages and disadvantages, and dual-channel DDR memory technology is no exception. First of all, dual-channel memory needs to be used in pairs, which greatly reduces the flexibility of memory configuration. The more important point is that when purchasing memory, you must choose at least 2×64MB, 2×128MB..., which will double the user's memory budget. Secondly, although the theoretical value of dual-channel memory technology is very attractive, due to various factors, its actual application performance cannot be twice as high as single-channel DDR memory, and of course it cannot be 4 times higher than PC133SDRAM, because after all, Under some system conditions, the system performance bottleneck is more than just memory. It can be seen from some test results that the system using 128bit memory channel