What are expansion cards and why are they needed?

Steel Low Profile Expansion Slot Cover Plate - 5 Pack case expansion slot width This empty slot plate is specifically designed to cover blank low profile type PCI slots Applications Replace missing or damaged rear expansion card slot casino slot wolf 2x full-height & full-length expansion slot 2x AIOM expansion slot; 4 x 1U Redundant 700750W Single Output Power Supply Platinum level, width

ocean bed slot Width: cm Thickness: cm Weight: 207g Display Parameters Size: Protective Case OnePlus RCC Card Note 1 Relevant product parameter