DDR5 - What we know about the next generation of SDRAM

DDR5 - What we know about the next generation of SDRAM
All the way back in August of 2000, the first motherboard to support Double Data Rate Synchronous Dynamic Random-Access Memory (or DDR SDRAM for short) appeared on the market. Since then, every four or five years we’ve seen a new version of DDR memory released, each treating us to an increase in capacity, bandwidth, and transfer speeds, along with reductions in power consumption.

Now, with the impending release of Intel's 12th Generation Alder Lake, its support for DDR5 is becoming a key talking point on the advantages this new version of SDRAM brings over existing memory modules.

“The way to have power is to take it.”

Power management has undergone some big changes with DDR5. Up to and including DDR4, manufacturers of SDRAM have had to rely on motherboard manufacturers to supply their memory with the correct levels of power. By their nature, DDR5 SDRAM based memory subsystems require tighter tolerances when it comes to voltage, along with the fact that memory population is denser, so to mitigate all these factors DDR5 has switched from the old method of power extraction, i.e. drawing power from the motherboard, to a new one. DDR5 now has power rails directly on the DIMM, ensuring complete control over power management for the memory modules, more efficient scaling of power delivery, higher performance and density, all while reducing overall system power consumption.

Five more improvements DD5 brings over DDR4

Higher bandwidth
With each iteration of DDR SDRAM, the maximum data rate available has increased gradually, peaking with DDR4 at 3.2Gbps. According to Rambus however, the company who essentially outlines the specification for DDR memory, DDR5 bucks this gradual increase by jumping to a remarkable starting data rate of 4.8Gbps, with the ability to scale that up to 6.4Gbps — double the maximum of its predecessor, DDR4.

Lower voltage
As we continue to transition to a world where decreasing power consumption is as much a consideration as increasing performance, every iteration of DDR memory released has marked reduction in power usage. DDR5 is no different with power usage clocking in at just 1.1V, which is even more significant when we take into consideration the huge leap in bandwidth capabilities, and the fact DDR4 operates at 1.2V. This lower power usage does decrease the memory’s tolerance to noise however, although electromagnetic interference is far less common now than perhaps ten years ago.

Channel Architecture
New DIMM channel architecture makes its way into DDR5 with a view to increasing memory access efficiency across the board. Where DDR4 DIMMs have a single 72-bit bus comprising 64 data bits, each DDR5 DIMM has two channels with the same 64 data bits split between them. Although the data width is exactly the same the efficiency of data access is improved by having two smaller channels. Furthermore, the potential issue of being susceptible to noise is addressed by the increase in the count of output clocks from DDR4’s two up to four, as this increases signal integrity by lowering the VDD.

Longer Burst Length
The term Burst Length refers to the amount of data passed between the CPU and memory during each transmission, and the greater the burst length, the more data can be accessed in one go. DDR5 has doubled the burst length over DDR4 from eight 64-bit words to sixteen 64-bit words, which equates to 64 bytes of data, or the typical size of a CPU cache line. Where DDR4 would have to retrieve data eight words at a time, DDR5 can more often than not retrieve entire cache lines with each transmission, which of course increases the speed of data transfer.

Higher capacity
We mentioned earlier that we’ve seen an increase in density capabilities for DDR5 systems. For those unsure, density describes the number of small black DRAM chips attached to the side of the memory module, and the more there are, the more “dense” the module is, and higher the capacity of memory that can be fit into a system.

DDR4 topped out at a 16 Gigabits per die, meagre when you compare it to the four-fold increase to 64 Gigabits per die that DDR5 brings to the table. As DRAM series mature, the density available per module increases, and following trends in previous iterations DDR5 is expected to rise to an impressive 128GB per die.

In summary

DDR5 is set to offer more efficient, faster memory in higher capacities while using less power. Current pricing doesn't seem to vary too much, but system memory is a volatile market at the best of times. DDR5 SO-DIMM and DIMM modules have already been released by memory manufacturers like Team Group, so we don't expect it will be long before our manufacturing partners release a range of embedded computers and single board computers that feature Alder Lake processors, which will take advantage of the benefits offered by the new DDR5 memory platform.
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Sep 2021
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