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Several types of memory configuration available:
Single channel (asymmetric) mode
This mode is equivalent to single channel bandwidth operation for applications. This mode is used when only one DIMM is installed or the memory capacities are unequal. Technology and device width can vary from one channel to the other. When using different speed DIMMs between channels, the slowest memory timing is also used.
Memory configuration for single channel mode
Single channel (asymmetric) mode configuration with One DIMM
Single channel (asymmetric) mode configuration 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, in fact, is capable of dual channel mode. If you shut down and rearrange the DIMMs properly, you can establish dual channel mode.
Memory channel speed is decided by the slowest DIMM module populated in the system.
Dual channel (interleaved) mode
This mode offers high throughput for applications. Dual channel mode is enabled when the installed memory capacities of both DIMM channels are equal. Technology and device width can vary from one channel to the other but the installed memory capacity for each channel must be equal. When using different speed DIMMs are used between channels, the slowest memory timing will be used.
Memory configuration for dual channel mode
Dual channel mode can be achieved with two, three, or four DIMMs.
Dual channel (interleaved) mode configuration with two DIMMs
Dual channel (interleaved) mode configuration with three DIMMs
Dual channel (interleaved) mode configuration with four DIMMs
Rules to enable dual channel mode
To achieve dual channel mode, the following conditions must be met:
- Matched DIMM configuration in each channel
- Same density (128 MB, 256 MB, 512 MB, etc.)
- Matched in both Channel A and Channel B memory channels
- Populate symmetrical memory slots (Slot 0 or Slot 1)
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 DDR speed
Memory channel speed is decided by the slowest DIMM module populated in the system.
Triple channel mode
This mode offers the high throughput for applications. 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 memory channels (blue connectors).
- If only two of the blue memory connectors are populated with matched DIMMs, dual channel memory is enabled.
Quad channel mode
This mode is enabled when 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 system will operate in dual-channel mode. When three memory modules are installed, the system will operate in triple-channel mode.
Quad channel mode with four DIMMs:
Quad channel mode with eight DIMMs:
Flex mode
This mode offers the most flexible performance characteristics. The lowest DRAM memory in the system memory map is mapped to dual channel operation; the DRAM memory nearest to the 8 GB address space limit, if any, is mapped to single channel operation. Flex mode results in multiple zones of dual and single channel operation across the whole of DRAM memory. To use flex mode, both channels must be populated.
Memory configuration for flex mode
For the use of flex mode, DIMMs must be installed in both channels.
The figure below shows a flex mode configuration using two DIMMs. The operation is as follows:
- The 512 MB DIMM in the Channel A, DIMM 0 socket and the lower 512 MB of the DIMM in the Channel B, DIMM 0 socket operate together in dual channel mode.
- The remaining (upper) 512 MB of the DIMM in Channel B operates in single channel mode.
This applies to:
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