EMZETT.DDR memory: from DDR to DDR5
In short: DDR (double data rate) is the design of today’s main memory modules. Each generation (DDR, DDR2, DDR3, DDR4, DDR5) is faster and more frugal but not compatible with the others.
In more detail: The name describes that data is transferred per clock cycle on the rising and falling edge of the clock signal, i.e. twice as much as with a single edge. Each new generation raises the data rate, lowers the voltage and extends the architecture.
In Depth
| DDR | DDR2 | DDR3 | DDR4 | DDR5 | |
|---|---|---|---|---|---|
| Year | 2000 | 2003 | 2007 | 2014 | 2020 |
| Voltage | 2.5 V | 1.8 V | 1.5 V (1.35 V LV) | 1.2 V | 1.1 V |
| Data rate (MT/s) | 200 – 400 | 400 – 1066 | 800 – 2133 | 1600 – 3200+ | 4800 – 8000+ |
| Prefetch | 2n | 4n | 8n | 8n | 16n |
| Modules | 184 pin | 240 pin | 240 pin | 288 pin | 288 pin |
| Typical size/module | up to 1 GB | up to 4 GB | up to 16 GB | up to 64 GB | up to 128 GB |
| Special | – | More frugal than DDR | Higher density | Bank groups, lower voltage | Voltage regulator on module, two sub-channels, on-die ECC |
Comparison along the aspects of the task:
- Speed: Per generation the data rate roughly doubles. DDR3-1600 delivers 12.8 GB/s, DDR4-3200 25.6 GB/s, DDR5-6400 51.2 GB/s per module. Latency in nanoseconds stays similar; the higher number in cycles (CL) is offset by a higher clock.
- Voltage: Drops from 1.5 V (DDR3) to 1.2 V (DDR4) and 1.1 V (DDR5). Less voltage means less waste heat and power, important for notebooks and servers.
- Architecture: DDR4 introduces bank groups. DDR5 splits each module into two independent 32-bit channels, has its own voltage regulator (PMIC) on the module (instead of on the motherboard) and integrated error correction (on-die ECC) that catches instability at high data rates. Burst length rises to 16.
Further terms:
- Data rate (MT/s) versus clock (MHz): DDR4-3200 runs at a real clock of 1600 MHz but transfers 3200 million transfers per second. The label “PC4-25600” gives MB/s.
- Timings: CL16-18-18-38 gives wait cycles. Lower is better, only when compared at the same clock.
- XMP/EXPO: Overclocking profiles stored by the manufacturer that you enable in the UEFI.
- Dual channel: Two modules in parallel double the bandwidth.
- Compatibility: Modules are protected against wrong insertion by different notches. DDR4 does not fit DDR5 boards.
- Mobile variants: SO-DIMM (notebook), LPDDR (soldered, very frugal).
- Graphics memory: GDDR is related but tuned for bandwidth instead of latency.
See also: RAM, RAM, [[rom-(festwertspeicher)|ROM and non-volatile storage]], How CPU, memory and motherboard interact