Both the R840 and R940 are 4-socket PowerEdge servers, but in different form factors. The R840 is 2U (dense), while the R940 is 3U (more expansion).
Comparison
| Feature | R840 (2U) | R940 (3U) |
|---|---|---|
| CPU Sockets | 4 | 4 |
| Memory | 48 DIMMs, 6TB | 48 DIMMs, 6TB |
| Drive Bays | 8 SFF | 16 SFF + 4 NVMe |
| PCIe Slots | 6 | 12 |