SK-Hynix Plans for Blazing-Fast DDR5-8400 PC Memory

SK Hynix is making big around DDR5, including an unprecedented effort to ramp the standard’s clock speed much higher than we typically see in a single RAM generation. Currently, a dual-channel DDR4-3200 solution offers up to 51.7GB/s of memory bandwidth. A dual-channel DDR5-8400 solution would push this to a massive 134.4GB/s of RAM per second.

To hit these heights, a number of changes to DDR5 are required compared with DDR4, and Hynix has released information on how it plans to achieve these goals.

SK_hynix_DDR5_Specifications

Many of these are unsurprising extensions of capabilities baked into DDR4. DDR5 uses 32 banks in eight groups compared with DDR4’s 16 banks in four groups, and a doubled burst length (from 8 to 16). Other features are new (or new as baseline capabilities).

ECC (Error Correcting Code) is not a new DRAM feature, but this is the first time we’ve seen mandatory on-die ECC built into a consumer RAM standard.

Another advantage that should boost overall throughput is a capability named Same Bank Refresh (abbreviated as REFsb for reasons that escape me). Previously, DRAM refresh cycles targeted every DRAM bank simultaneously and read/write commands can’t be processed during a refresh cycle. According to this Micron whitepaper, an All-Bank Refresh is issued an average of every 3.9µs and takes 295ns to complete.

Same Bank Refresh only requires that one bank in each bank group be idle in order for the command to process. The other 12 banks do not have to idle and can continue to operate normally. REFsb commands are issued every 1.95µs but complete in 130ns. Using REFsb reduces the impact on idle latency from 11.2ns to 5ns. Latency-reducing tricks are generally much harder to pull off than throughput improvements, so every bit helps in virtually every area.

According to Micron, REFsb improves throughput by 6-9 percent depending on the mixture of reads versus writes in the test. DDR5 should have higher throughput than DDR4 even at the same frequency, though obviously the difference isn’t huge.

DDR5’s operating voltage is also reduced compared to DDR4, down to 1.1v, though the higher clock speeds enthusiasts favor will undoubtedly draw more power than the standard modules (especially if Hynix makes good on that DDR5-8400 promise).

As for when you should actually expect to buy a system with DDR5? That’s far less clear. AMD is sticking with AM4 and DDR4 through 2020 and DDR5 is still just ramping up as far as production is concerned. We might see DDR5 in 2021, but it wouldn’t be unprecedented for its introduction to slip into 2022 — Intel and AMD have delayed adopting RAM standards in the past if price targets or overall product demand wasn’t being met.

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