Do all PCs have a PCIE slot? If they don't, can we upgrade our RAM

Anyone have a suggestion on a new PC that still has a PCI slot in it? I prefer HP or Lenovo EliteDesk 800 and ThinkCentre M73

-A AX6 II-CSM Ready For Advanced AI PC PRIME B650M-A AX6 II-CSM out of 5 stars AMD B650 Micro-ATX motherboard, DDR5, PCIe support,

pcie x16 slot Small form factor computers with PCIe expansion slots are delivering powerful compute power in a compact size for edge deployments

pcie slot splitter This definitely isn't your regular old mini PC something's up! Check out the full video here