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Yes—some DRAM-less NVMe SSDs can use a small, host-allocated portion of system memory through a feature called Host Memory Buffer (HMB). The SSD and the host must both support it. HMB is reserved for the drive controller’s use; it does not mean the SSD is putting your documents or other ordinary files in RAM.
How an SSD can use system RAM
HMB, introduced with NVMe 1.2, lets a compatible NVMe SSD use a region of the computer’s DRAM that the host allocates for it. NVM Express describes the allocation as system memory set aside for the SSD’s exclusive use, with translation tables as one example of what may go there.
That capability is conditional, not a feature of every SSD. The drive must implement HMB, and the host operating system and platform must support and enable the allocation. A DRAM-less design can therefore use host memory when those conditions are met, but it does not acquire the same hardware as an SSD with onboard DRAM.
What the buffer is used for
An SSD needs to map logical addresses requested by the computer to locations in its flash memory. In the commercial DRAM-less drives Kim and Kim evaluated, the authors found that HMB was used mainly to cache this flash translation layer address-mapping information—not as a general read cache for user files or as a write buffer. That finding applies to the devices in their study; drive makers can implement the feature differently.
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Because HMB holds controller metadata, it should not be understood as extra storage capacity or as a place where the drive keeps a general copy of the files being read and written.
How much RAM does an NVMe SSD use?
There is no single HMB allocation size that applies to all drives or computers. Microsoft’s NVMe documentation expresses the HMB size in memory-page units, while the actual allocation depends on the drive’s implementation and host configuration.
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For scale, Kim and Kim reported that, in their experimental setup, two tested devices could allocate between 8 MB and 480 MB, while another could allocate 64 MB. Those are capabilities observed for specific devices under the paper’s setup—not a promise about what a current system will allocate. Avoid assuming that every HMB-capable SSD takes a fixed amount of RAM.
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Does HMB make a DRAM-less SSD as fast as one with onboard DRAM?
Not necessarily. Kim and Kim tested six SSDs: three DRAM-less models that supported HMB and three models with internal DRAM. Their results showed HMB improved performance for the tested HMB-capable drives, but the DRAM-less drives performed worse than the internal-DRAM drives in many of the study’s results. These findings are limited to the devices and workloads tested; they do not establish a universal ranking or predict every drive’s performance.
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HMB is best understood as a way for some DRAM-less NVMe drives to use host memory for controller work, not as proof that they match drives with onboard DRAM. The practical difference depends on the particular SSD and the workload.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to check when comparing SSDs
Do not infer HMB support—or a particular performance level—from “NVMe” or “DRAM-less” alone. Check the documentation for the exact model and consider these factors together:
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- Controller memory: Is DRAM onboard, or is the drive DRAM-less?
- HMB support: Does the manufacturer document HMB for this specific model?
- Host compatibility: Does the computer’s operating system and platform support the feature, and is the drive compatible with the host interface?
- Capacity and warranty: Do the capacity and warranty meet your needs?
- Your workload: Look for performance information relevant to the kind of use you expect rather than assuming one design always wins.
HMB support alone cannot settle a buying decision: it says that a compatible drive may use host memory, not how fast it will perform in every task.
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