MSI H61M-P20 (G3) - Manual (Page 17)

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MS-7788
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iMPortANt
in dual-Channel mode, make sure that you install memory modules of the same
type and density in different channel diMM slots.
to enable successful system boot-up, always insert the memory modules into
the diMM first.
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*
installing Memory Modules
the memory module has only one notch on the center and will only fit in the
right orientation.
insert the memory module vertically into the diMM slot. then push it in until
the golden finger on the memory module is deeply inserted in the diMM slot.
you can barely see the golden finger if the memory module is properly in-
serted in the diMM slot.
the plastic clip at each side of the diMM slot will automatically close.
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