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Single- and Multichannel Memory Modes


Last Reviewed: 16-Mar-2016
Article ID: 000005657

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

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 with one DIMM
single-channel with one DIMM

Single-channel with three DIMMs
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.

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
dual-channel with 2 DIMMs

Dual-channel with three DIMMs
dual-channel with 3 DIMMs

Dual-channel with four DIMMs
dual-channel with 4 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.
triple-channel mode

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.

Quad-channel with four DIMMs:
quad-channel with 4 DIMMs

Quad-channel with eight DIMMs:
quad-channel with 8 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.
flex
Related topics
System memory information for your board
Troubleshooting system memory issues
Multi-channel memory architecture

This article applies to: