DDR4
What Is DDR4 Memory?
DDR4 stands for Double Data Rate 4 Synchronous Dynamic Random-Access Memory, commonly called DDR4 SDRAM. It is the memory generation that succeeded DDR3 and preceded DDR5.
DDR4 was extensively adopted by enterprise servers and workstations. Server implementations commonly use ECC-capable DDR4 RDIMMs and LRDIMMs, while desktops and other systems may use DDR4 UDIMMs. The correct memory type depends on the processor, motherboard and system architecture.
DDR4 Memory at a Glance
DDR4 identifies a memory generation. It does not by itself identify whether a module is ECC, registered, load-reduced, unbuffered, single-rank, dual-rank or another supported configuration.
Fourth-Generation DDR
DDR4 succeeded DDR3 and was later succeeded by DDR5.
1.2 V Standard
Standard DDR4 operates at a nominal 1.2 V, reducing operating voltage compared with standard DDR3.
Higher Transfer Rates
DDR4 provides higher transfer rates than the preceding DDR3 generation, with common server speeds extending through DDR4-3200.
Major Server Standard
DDR4 became a major enterprise memory technology across multiple generations of Intel Xeon and AMD EPYC servers.
How Does DDR4 Memory Work?
DDR4 is synchronous DRAM used as high-speed temporary system memory. The processor's memory controller communicates with installed DDR4 DIMMs through one or more memory channels, allowing the processor to rapidly read and write data required by applications, virtual machines, databases and operating systems.
Common DDR4 Memory Speeds
Enterprise DDR4 spans multiple transfer rates. The actual operating speed is determined by the processor, server platform, DIMM type and memory population.
| DDR4 Designation | Transfer Rate | Common PC4 Rating | General Context |
|---|---|---|---|
| DDR4-2133 | 2133 MT/s | PC4-17000 / PC4-17066 | Earlier DDR4 server platforms |
| DDR4-2400 | 2400 MT/s | PC4-19200 | Common enterprise DDR4 speed |
| DDR4-2666 | 2666 MT/s | PC4-21300 / PC4-21333 | Widely deployed server speed |
| DDR4-2933 | 2933 MT/s | PC4-23400 / PC4-23466 | Later enterprise DDR4 platforms |
| DDR4-3200 | 3200 MT/s | PC4-25600 | High-speed later DDR4 server platforms |
PC4 naming and rounded bandwidth values may vary by manufacturer. Always verify the complete module part number and server specifications when determining compatibility.
What Does PC4 Mean?
PC4 is the bandwidth-oriented naming convention associated with DDR4 memory. For example, DDR4-3200 is commonly identified as PC4-25600. DDR4-3200 describes the transfer rate, while PC4-25600 represents the module's approximate theoretical bandwidth in MB/s.
Enterprise module labels frequently include additional information describing capacity, rank, device organization, ECC capability and DIMM architecture. The entire specification matters when selecting server memory.
Types of DDR4 Server Memory
DDR4 is the memory generation, while UDIMM, RDIMM and LRDIMM describe different DIMM architectures. The server determines which architecture is supported.
DDR4 UDIMM
DDR4 unbuffered DIMMs are common in desktops and workstations and are supported by certain server platforms. ECC and non-ECC variants exist.
Learn About UDIMM →DDR4 RDIMM
DDR4 registered DIMMs are extensively used in enterprise servers. The register buffers command, address and control signals to support scalable server memory configurations.
Learn About RDIMM →DDR4 LRDIMM
DDR4 load-reduced DIMMs use additional buffering to reduce electrical loading on the memory controller and support high-capacity configurations on compatible servers.
Learn About LRDIMM →What Is DDR4 ECC Memory?
DDR4 ECC memory is DDR4 memory used in an ECC-capable memory subsystem. ECC, or Error-Correcting Code, provides mechanisms designed to detect and correct certain memory errors when supported by the processor, motherboard and system configuration.
ECC and registered memory are not synonymous. A DDR4 module can, for example, be an ECC UDIMM or an ECC RDIMM. The complete module architecture must match the requirements of the server or workstation.
DDR3 vs DDR4: What Changed?
| Characteristic | DDR3 | DDR4 |
|---|---|---|
| Generation | Third-generation DDR | Fourth-generation DDR |
| Standard Voltage | Typically 1.5 V | 1.2 V nominal |
| Bandwidth | Lower generation bandwidth | Higher generation bandwidth |
| Desktop DIMM Pins | 240-pin | 288-pin |
| Interchangeable? | No | No |
DDR4 vs DDR5: Is DDR5 a Direct Replacement?
No. DDR5 is the successor to DDR4, but DDR4 and DDR5 are not interchangeable. Each generation requires a compatible processor, memory controller, motherboard and DIMM architecture.
A DDR4 server cannot be upgraded to DDR5 simply by replacing its DIMMs. Moving to DDR5 generally requires a newer server platform designed specifically for DDR5 memory.
Not All DDR4 Server Memory Is Interchangeable
Two modules can both be labeled DDR4 and still be incompatible with one another or with the same server. Capacity, speed, ECC, DIMM architecture, rank, device organization and server memory population rules can all affect compatibility.
In particular, do not assume that DDR4 UDIMMs, RDIMMs and LRDIMMs can be mixed. A server may support more than one DIMM architecture in separate configurations while prohibiting those memory types from operating together.
DDR4 Memory Rank Explained
Memory rank describes how DRAM devices on a DIMM are electrically organized. Server platforms can impose limits on the number and type of ranks supported per channel.
Single Rank
A single-rank DIMM contains one independently addressable rank of memory.
Dual Rank
Dual-rank DIMMs contain two independently addressable memory ranks.
Higher Rank Configurations
High-capacity enterprise modules may use additional rank organization or memory technologies supported by the server platform.
Does Faster DDR4 Always Make a Server Faster?
Not necessarily. A DDR4 DIMM's rated speed does not guarantee that it will operate at that speed in every server. The processor's memory controller, DIMMs per channel, memory type and population configuration can determine the actual operating speed.
Server performance also depends on memory capacity, channel utilization, workload behavior and processor architecture. For virtualization and database workloads, having sufficient memory capacity can be just as important as transfer rate.
How to Identify DDR4 Server Memory
DDR4 Server Memory Compatibility
DDR4 compatibility involves much more than matching the DDR generation. The server model, processor, memory controller, DIMM architecture, capacity, speed, ECC capability, rank, device organization and memory population rules can all affect whether a module is supported.
When upgrading an enterprise server, identify the exact system model and currently installed memory before selecting additional DDR4 DIMMs.
What to Check Before Buying DDR4 Server Memory
DDR4 Memory FAQ
What does DDR4 stand for?
DDR4 stands for Double Data Rate 4 and identifies the fourth generation of DDR SDRAM.
What is PC4 memory?
PC4 is a bandwidth-oriented naming convention associated with DDR4 memory.
What voltage does DDR4 use?
Standard JEDEC DDR4 memory uses a nominal 1.2 V supply.
Is DDR4 server memory ECC?
Many enterprise DDR4 server configurations use ECC memory, but DDR4 itself does not mean ECC. ECC and non-ECC DDR4 modules exist.
What is DDR4 RDIMM?
A DDR4 RDIMM is a registered DIMM using DDR4 technology. RDIMMs are widely used in enterprise servers.
What is DDR4 LRDIMM?
A DDR4 LRDIMM is a load-reduced DIMM designed to reduce electrical loading and support high-capacity server memory configurations on compatible platforms.
Can DDR3 and DDR4 be mixed?
No. DDR3 and DDR4 are different memory generations with different electrical and physical specifications.
Can DDR4 and DDR5 be mixed?
No. DDR4 and DDR5 require platforms specifically designed for their respective memory generation.
What is the fastest common DDR4 server memory?
DDR4-3200 is a common high-end JEDEC DDR4 server memory speed, although actual operating speed depends on the processor and platform.
Can faster DDR4 RAM work in a slower server?
Some platforms can operate a faster-rated compatible DIMM at a lower supported speed, but compatibility must be verified for the exact server and configuration.
Can RDIMM and LRDIMM be mixed?
Generally, server memory types should not be assumed to be mixable. Follow the exact memory population rules for the server platform.
How do I know which DDR4 memory I need?
Identify the server model, processor, DIMM type, ECC requirement, capacity, speed, rank and currently installed memory before selecting a replacement or upgrade.