DDR4 vs DDR5

DDR4 is the fourth generation of double data rate (DDR) system memory, with one 64-bit channel per module and speeds up to 3,200 megatransfers per second (MT/s). DDR5 is the fifth generation, with two independent 32-bit subchannels per module and speeds starting at 4,800 MT/s. DDR5 also moves voltage regulation onto a power management integrated circuit (PMIC) on each module. Its key notch sits in a different place, so neither fits the other's slot.

DDR4 runs at 1.2 V and DDR5 at 1.1 V. DDR5 doubles the burst length to 16, so one 32-bit subchannel fills a 64-byte cache line by itself. It also allows 64 Gb DRAM dies against 16 Gb for DDR4, which lifts the single-die module ceiling from 64 GB to 256 GB. Every DDR5 chip carries on-die error-correcting code (ECC) that fixes single-bit errors before data leaves the chip. That is not ECC memory. Server ECC modules add 8 check bits per 64-bit DDR4 channel and per 32-bit DDR5 subchannel, for the memory controller to verify.

A board takes DDR4 or DDR5, never both, so the platform decides the generation. On either one, specify ECC modules wherever a silent bit flip would corrupt a result, because DDR5's on-die ECC does not replace them.

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Last verified October 7, 2026.