How do I upgrade from 2 sticks of RAM to 4?

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I tried to boot using only one RAM bar at a time in DIMM_A2, DIMM_B1 and DIMM_B2, but the PC wouldn't boot 2 RAM bars, one is DIMM_A1 and one in DIMM_A2 PC Boost Your Computer's Performance: RAM in Slots 2 and 4 • Enhance Performance: RAM in 2

which technology is particularly used in barcode wand reader and barcode slot reader Different types of RAM slots exist, such as DDR4 and DDR5, each compatible with specific RAM modules Modern motherboards usually come with 2-4 : 2 ram slot motherboard FRONTECH H61 Chipset Motherboard with 2xDDR3 RAM Slots LGA1155 Supports i3i5i7Pentium Processors 6+4 USB Ports