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Some DRAM-less NVMe SSDs can borrow a small portion of your computer’s RAM through Host Memory Buffer (HMB). The drive uses that memory for an internal task—often keeping address-mapping information handy—not as a large, general-purpose cache for your files. HMB can help particular workloads, but it does not guarantee the performance of an SSD with its own DRAM, especially during long writes.
What Host Memory Buffer does
Host Memory Buffer is an NVMe feature introduced with NVMe 1.2, according to a peer-reviewed study published in 2020. It allows a compatible SSD to use a portion of host DRAM for a purpose chosen by the drive maker. Both the SSD and the operating system must support HMB for it to be activated. The study’s explanation of HMB and its tests describes this arrangement.
HMB does not add DRAM to the SSD itself. Nor should “uses system RAM” be read as meaning the drive borrows a large pool of memory to cache all incoming or outgoing data. In the six drives examined by the study, the HMB models mainly used host memory to cache address-mapping information: data that helps the SSD locate where files are stored in NAND flash. That finding applies to those particular drives, and manufacturers’ internal designs may differ.
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The study compared three commercial DRAM-less HMB drives with three drives that had onboard DRAM. It used light and heavy workloads involving sequential and random reads and writes. HMB improved some tested patterns, including random reads, but the DRAM-less drives had worse I/O performance in many results. The researchers did not establish a single percentage improvement that applies to all HMB drives.
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That variation matters because SSD performance depends on the drive’s design and the work being done. A feature that helps with address lookups in one workload does not necessarily make a drive match an onboard-DRAM model across every workload. Short benchmark runs can also miss behavior that appears only after a drive’s secondary write cache is exhausted.
Why a fast short test may not predict a large transfer
HMB is only one part of an SSD’s performance story. NAND type, capacity, firmware, system configuration, and the drive’s write-cache behavior can also affect results. A PCWorld review published April 22, 2025, tested one 2 TB Teamgroup MP44Q, a PCIe 4.0 QLC SSD with HMB. The reviewer found strong everyday performance, but reported write speeds of 100–135 MB/s once transfers exceeded the tested drive’s secondary-cache conditions. PCWorld’s review cautions that performance can vary with capacity and drive components.
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Those speeds are a result for that specific 2 TB sample and review workload, not an HMB limit or a prediction for all QLC or DRAM-less SSDs. They illustrate why a short benchmark result and a long sustained-write result answer different questions.
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Samsung’s 2021 announcement described the Samsung 980 as a DRAM-less consumer SSD using HMB and listed maximum sequential read and write specifications of 3,500 MB/s and 3,000 MB/s. Those are Samsung’s announced specifications, not independent measurements. Samsung’s announcement and its Canadian product page provide the company’s description; the latter says performance varies with firmware, system, and hardware configuration.
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The example shows that an HMB drive can carry strong vendor-rated sequential specifications. It does not establish how that exact drive performs in every workload, or prove parity with an onboard-DRAM SSD. Manufacturer specifications and independent tests should be treated as different kinds of evidence.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to compare HMB and onboard-DRAM SSDs
If you are deciding whether DRAM-less is suitable, match the evidence to what you actually do with the drive. A sequential speed rating is not a substitute for workload-specific measurements.
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- Match the exact model and capacity. A review of one capacity or revision should not automatically stand in for another.
- Check random-read behavior if your use involves frequent small file access or mixed workloads; HMB’s address-mapping role can matter here.
- Look for sustained-write tests that continue beyond the secondary write cache, especially if you often move large files or write substantial amounts of data.
- Note the NAND type and other drive design details when available; they can shape behavior independently of HMB.
- Separate specifications from measurements. Record whether a number comes from a manufacturer or an independent reviewer, along with the workload and test method.
For ordinary day-to-day use, an HMB drive may be a sensible fit if its tested behavior suits your workload. If sustained large writes matter, prioritize reviews that test beyond cache exhaustion rather than relying on a short sequential benchmark. There is no universal rule that HMB makes a drive either equivalent to onboard DRAM or inherently too slow.
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