Dell External OEMR R420 Owner's Manual page 38

Figure 11. Inside the System—With a Non-Redundant Power Supply
1. cooling shroud
2. power supply unit
3. storage controller card
4. expansion-card riser 2
5. expansion card
6. expansion-card riser 1
7. heat sink for processor 2
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8. DIMMs (12)
9. cooling fans (5)
10. optical drive
11. hard drives (4)
12. front I/O panel
13. cable routing latch