DRAMless vs DRAM NVMe SSDs

DRAMless vs DRAM NVMe SSDs

When you look at NVMe SSD specifications, you will notice that some drives have a DRAM cache and others do not. DRAM is the same type of memory used for system RAM, and on an SSD it serves as a mapping table that keeps track of where data is stored on the NAND chips. Without DRAM, the drive has to store this mapping table on the NAND itself, which is much slower.

The mapping table, also called the Flash Translation Layer, is essential for SSD operation. When the operating system wants to read a file, it sends a logical block address to the SSD. The controller needs to translate that logical address into a physical location on the NAND chips. With DRAM, this translation happens instantly. Without DRAM, the controller has to read the mapping table from the slow NAND first.

DRAMless drives have become very common because they are cheaper to manufacture. To compensate for the missing DRAM, modern DRAMless drives use a technology called Host Memory Buffer, or HMB. HMB reserves a small portion of your system RAM for the SSD to use as its mapping table. This works surprisingly well, and for most everyday tasks, the difference between a DRAMless drive with HMB and a DRAM drive is small.

The problem with DRAMless drives shows up under heavy workloads. If you are doing sustained writes, like copying large files or running a database, the DRAMless drive will slow down significantly. The HMB helps, but it is not as fast as dedicated DRAM on the drive itself. For gaming and general use, this is rarely an issue, but for professional workloads, a DRAM drive is worth the extra cost.

How can you tell if a drive has DRAM? Check the specifications. If it mentions DDR3 or DDR4 memory on the drive, it has DRAM. If it mentions HMB, it is DRAMless. Some budget drives have neither DRAM nor HMB, and these should be avoided. For a boot drive, a DRAM drive is recommended. For a secondary game storage drive, a good DRAMless drive with HMB is perfectly fine.