QNAP TS-873U - System Board; Front Drive Numbering

System Board
No. Component No. Component
1 DIMM memory slot 4 5 M.2. SSD slot 1
2 DIMM memory slot 3 6 M.2. SSD slot 2
3 DIMM memory slot 2 7 PCIe 3.0 x4
4 DIMM memory slot 1 - -
Front Drive Numbering
TS-873U, TS-873U-RP
TS-x73U User Guide
Product Overview 10