MSI B550M-A PRO Manuel D'instructions page 9

DIMM Slots
Please install the memory module into the DIMM slot as shown below.
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Important
Due to chipset resource usage, the available capacity of memory will be a little less
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than the amount of installed.
Please note that the maximum capacity of addressable memory is 4GB or less
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for 32-bit Windows OS due to the memory address limitation. Therefore, we recom-
mended that you to install 64-bit Windows OS if you want to install more than 4GB
memory on the motherboard.
PCI_E1~2: PCIe Expansion Slots
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Important
If you install a large and heavy graphics card, you need to use a tool such as MSI
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Gaming Series Graphics Card Bolster to support its weight to prevent deformation
of the slot.
When adding or removing expansion cards, always turn off the power supply and
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unplug the power supply power cable from the power outlet. Read the expansion
card's documentation to check for any necessary additional hardware or software
changes.
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PCI_E1: PCIe 3.0 x1 (PCH)
PCI_E2: PCIe 4.0/ 3.0 x16 (CPU)
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Overview of Components
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