Server Memory Explained: How to Read a RAM Label
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A memory module's label looks like a code, but every part of it tells you something you need to match. Take a typical server module:
8GB 2Rx4 PC3L-10600R
8GB is the capacity of the module.
2Rx4 is the layout. 2R means dual rank, and x4 describes the width of the memory chips. Servers can be particular about rank, so match it when adding to existing memory.
PC3L is the generation and voltage. PC3 is DDR3, PC4 is DDR4, and PC2 is DDR2. The L means low voltage, 1.35V in place of the standard 1.5V for DDR3.
10600 is the speed. DDR3 labels give a transfer rate, so PC3-10600 is DDR3 at 1333MHz and PC3-12800 is 1600MHz. DDR4 labels give the speed directly, such as PC4-2400T.
R is the module type, and it is the letter that matters most.
| Letter | Type | Used in |
|---|---|---|
| R | Registered (RDIMM) | Most servers and some workstations |
| L | Load-reduced (LRDIMM) | High-capacity servers |
| E | Unbuffered ECC | Entry-level servers and some workstations |
| U | Unbuffered (UDIMM) | Desktop PCs |
| S | SODIMM | Laptops and small form factor PCs |
The rules that catch people out
- A server built for registered memory will not start with unbuffered desktop memory, and a desktop will not accept registered memory.
- Registered and load-reduced modules cannot be mixed in one server.
- DDR3 and DDR4 modules have the notch in different places and do not fit each other's slots.
- Faster memory generally works in a slower system but runs at the slower speed. The whole system runs at the speed of its slowest module.
Manufacturer part numbers
Memory sold by Dell, HP, IBM or Lenovo carries that company's part number as well as the memory maker's own, such as a Samsung or Micron number. Either can be used to find the same module. Some servers show a warning with memory that doesn't carry their own brand's number, so matching the server maker's part number is the safest route.
Before you order
Note down the full label from a module already in the machine, and check how many slots are free. Then browse our tested memory. If you are unsure, send us the label details and the system model.