Why Are Dimm Slots Different Colors

Dual-channel capable board, with 4 DIMM slots in 2 different colors-questions. Thread starter DastardlyDan; Start date Dec 14, 2010; DastardlyDan Posts: 14 +0. Dec 14, 2010 #1.
DIMM (dual in-line memory module) slots are the place on your motherboard where the RAM goes. As such, you may also see DIMM slots referred to as “RAM slots.”.

The slots having the matching colors are paired, so a matched set of memory modules would plug into the slots having the white tabs, and likewise for the slots having the black tabs. For best performance you need to install memory beginning with the first slot, which is usually a white tab, I think.

Memory Channels

In the fields of digital electronics and computer hardware, multi-channel memory architecture is a technology that increases the data transfer rate between the DRAM memory 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.

Single-channel (asymmetric) mode
This mode provides single-channel bandwidth operations and is used when only one DIMM is installed or when the memory capacities of more than one DIMM are unequal. When using different speed DIMMs between channels, the slowest memory timing is also used.

Single Channel memory, with a maximum rated clock of 400 MHz and a 64-bit (8 bytes) data bus is now becoming obsolete and is not being produced in massive quantities. Technology is adopting new ways to achieve faster speeds/data rates for RAM memories.

Dual-channel architecture

Dual channel memory slots, color-coded orange and yellow for this particular motherboard.

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.

Dual-channel

architecture requires a dual-channel-capable motherboard and two or more DDR, 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 the memory controller access to each memory module. It is not required that identical modules be used (if motherboard supports it), but this is often recommended for best dual-channel operation.

Motherboards supporting dual-channel memory layouts typically have color-coded DIMM sockets. Coloring schemes are not standardized and have opposing meanings, depending on the motherboard manufacturer's intentions and actual motherboard design. Matching colors may either indicate that the sockets belong to the same channel (meaning that DIMM pairs should be installed to differently colored sockets), or they may be used to indicate that DIMM pairs should be installed to the same color (meaning that each socket of the same color belongs to a different channel). The motherboard's manual will provide an explanation of how to install memory for that particular unit. A matched pair of memory modules may usually be placed in the first bank of each channel, and a different-capacity pair of modules in the second bank.^[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 MiB). 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.
Same CAS Latency (CL) or Column Address Strobe.
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.

Performance

Theoretically, dual-channel configurations double the memory bandwidth when compared to single-channel configurations. This should not be confused with double data rate (DDR) memory, which doubles the usage of DRAM bus by transferring data both on the rising and falling edges of the memory bus clock signals.

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 Laptop logic resulted in a similar conclusion for integrated graphics.^[8] The test results published by Tom's Hardware had a discrete graphics comparison.

Another benchmark performed by TweakTown, using SiSoftware Sandra, measured around 70% increase in performance of a quadruple-channel configuration, when compared to a dual-channel configuration.^[9]^{:p. 5} Other tests performed by TweakTown on the same subject shown no significant differences in performance, leading to a conclusion that not all benchmark software is up to the task of exploiting increased parallelism offered by the multi-channel memory configurations.^[9]^{:p. 6}

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,^[10] 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.^[11]^[12]

'Ganged' versus 'unganged' difference could also be envisioned as an analogy with the way RAID 0 works, when compared to JBOD.^[13] With RAID 0 (which equals to 'ganged' mode), it is up to the additional logic layer to provide better (ideally even) usage of all available hardware units (storage devices, or memory modules) and increased overall performance. On the other hand, with JBOD (which equals to 'unganged' mode) it is relied on the statistical usage patterns to ensure increased overall performance through even usage of all available hardware units.^[11]^[12]

Triple-channel architecture

Operation

DDR3 triple-channel architecture is used in the IntelCore 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, 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.^[14]

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.

Why are dimm slots different colors used

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.^[15]

One of the differences between DDR, DDR2 and DDR3 is the highest transfer rate each generation can reach. Below is a list the most common speeds for each generation.

DDR memory's primary advantage is the ability to fetch data onboth the rising and falling edge of a clock cycle, doubling thedata rate for a given clock frequency. For example, in a DDR200device the data transfer frequency is 200 MHz, but the busspeed is 100 MHz.

DDR1, DDR2 and DDR3 memories are powered up with 2.5,1.8 and 1.5V supply voltages respectively, thus producing lessheat and providing more efficiency in power management thannormal SDRAM chipsets, which use 3.3V.

Why are dimm slots different colors like

Temporization is another characteristic of DDR memories.Memory temporization is given through a series of numbers,such as 2-3-2-6-T1, 3-4-4-8 or 2-2-2-5 for DDR1. Thesenumbers indicate the number of clock pulses that it takes thememory to perform a certain operation—the smaller the number,the faster the memory.

The operations that these numbers represent are the following:CL–tRCD–tRP–tRAS–CMD. To understand them, you haveto keep in mind that the memory is internally organized as amatrix, where the data is stored at the intersection of the rowsand columns.

CL: Column address strobe (CAS) latency is the time it takes between the processor asking memory for data and memory returning it.
tRCD: Row address strobe (RAS) to CAS delay is the time it takes between the activation of the row (RAS) and the column (CAS) where data is stored in the matrix.
tRP: RAS precharge is the time between disabling the access to a row of data and the beginning of the access to another row of data.
tRAS: Active to precharge delay is how long the memory has to wait until the next access to memory can be initiated.
CMD: Command rate is the time between the memory chip activation and when the first command may be sent to the memory. Sometimes this value is not informed. It usually is T1 (1 clock speed) or T2 (2 clock speeds).

igure 2: SMAC in Numbers
Memory	Technology	Rated Clock	Real Clock	Maximum Transfer Rate
PC66	SDRAM	66 MHz	66 MHz	533 MB/s
PC100	SDRAM	100 MHz	100 MHz	800 MB/s
PC133	SDRAM	133 MHz	133 MHz	1,066 MB/s
DDR200	DDR-SDRAM	200 MHz	100 MHz	1,600 MB/s
DDR266	DDR-SDRAM	266 MHz	133 MHz	2,100 MB/s
DDR333	DDR-SDRAM	333 MHz	166 MHz	2,700 MB/s
DDR400	DDR-SDRAM	400 MHz	200 MHz	3,200 MB/s
DDR2-400	DDR2-SDRAM	400 MHz	200 MHz	3,200 MB/s
DDR2-533	DDR2-SDRAM	533 MHz	266 MHz	4,264 MB/s
DDR2-667	DDR2-SDRAM	667 MHz	333 MHz	5,336 MB/s
DDR2-800	DDR2-SDRAM	800 MHz	400 MHz	6,400 MB/s
DDR3-800	DDR3-SDRAM	800 MHz	400 MHz	6,400 MB/s
DDR3-1066	DDR3-SDRAM	1066 MHz	533 MHz	8,528 MB/s
DDR3-1333	DDR3-SDRAM	1333 MHz	666 MHz	10,664 MB/s
DDR3-1600	DDR3-SRAM	1600 MHz	800 MHz	12,800 MB/s

Single Vs Double Sided ram

In SDRAM single sided (high density) can be used only in modern PCs. Old PCs don't always read the memory right because they calculate how much RAM to access based on the number of chips on the stick, not taking into account that each chip might contain twice the storage.
So for old PCs you should use double-sided (low density) RAM to ensure that it will work correctly in your system. Otherwise, the PC might end up convinced that your memory has only half the storage capacity that it is actually capable of.
To my knowledge, in SDRAM there is no real performance difference between the two. (Unlike with RDRAM which increases latency by the number of chips, so high-density is slightly faster than low-density.) So any modern PC that can properly use the single-sided (high density) SDRAM should be happy with whatever combination that you use.

Several types of memory modes can be configured on Intel® Desktop Boards, depending on how many memory modules (DIMMs) are installed:

Single-channel with one DIMM

Single-channel with three DIMMs

At boot, the memory configuration is detected and you might see this alert message:

Alert: Maximum memory performance is achieved with equal amounts of memory installed in each channel. Press any key to continue.

With the DIMMs that are currently installed, the computer is set to single-channel mode, but it can be set to dual-channel mode. If you shut down and rearrange the DIMMs properly, you can establish dual-channel mode.

Why Are Dimm Slots Different Colors Made

Dual-channel (interleaved) mode
This mode offers higher memory throughput and is enabled when the memory capacities of both DIMM channels are equal. When using different speed DIMMs, the slowest memory timing is used.

Dual-channel with two DIMMs

Why Are Dimm Slots Different Colors Like

Dual-channel with three DIMMs

Dual-channel with four DIMMs

Rules to enable dual-channel mode
To achieve dual-channel mode, the following conditions must be met:

Same memory size. Examples: 1 GB, 2 GB, 4 GB.
Matched DIMM configuration in each channel
Matched in symmetrical memory slots

Configurations that do not match the above conditions revert to single-channel mode. The following conditions do not need to be met:

Same brand
Same timing specifications
Same speed (MHz)

The slowest DIMM module populated in the system decides memory channel speed.

Triple-channel mode
Triple-channel interleaving reduces overall memory latency by accessing the DIMM memory sequentially. Data is spread through the memory modules in an alternating pattern.

Three independent memory channels give two possible modes of interleaving:

Triple-channel mode is enabled when identical matched memory modules are installed in each of the three blue memory slots.
If only two of the blue memory slots are populated with matched DIMMs, dual-channel mode is enabled.

Quad-channel mode
This mode is enabled when four (or a multiple of four) DIMMs are identical in capacity and speed, and are put in quad-channel slots. When two memory modules are installed, the system operates in dual-channel mode. When three memory modules are installed, the system operates in triple-channel mode.

Why Are Dimm Slots Different Colors Called

Quad-channel with four DIMMs:

Quad-channel with eight DIMMs:

Flex mode
This mode results in both dual and single-channel operation across the whole of DRAM memory. The figure shows a flex mode configuration using two DIMMs. The operation is as follows:

The 2 GB DIMM in slot 1 and the lower 2 GB of the DIMM in slot 2 operate together in dual-channel mode.
The remaining (upper) 2 GB of the DIMM in slot 2 operates in single-channel mode.