Back in the day, the presence of a DRAM (Dynamic Random Access Memory) cache was more or less a requirement if you wanted a well-performing SSD that won't choke under pressure. But thanks to one improvement, modern SSDs don't need a DRAM cache anymore to stay competitive.
Thanks to HMB, DRAM-less SSDs can be as performant as those with DRAM
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The role of the DRAM cache in an SSD is to maintain a "map" of files written to it that keeps track of their locations, improving overall performance. Older SSDs without a DRAM cache keep this mapping table in their flash memory , which is orders of magnitude slower than the DDR4 memory typically used for the DRAM cache. Without a DRAM cache, SSDs can deliver high sequential read and write performance but much slower random read and write performance, which is important for many operations, including operating system–related workloads.
But thanks to the HMB (Host Memory Buffer) technology, SSDs that don't include a DRAM cache can instead reserve a portion of your PC's memory to use as their DRAM cache. While storing the mapping table on external memory results in higher latency and lower performance than having the cache on a memory chip right on the SSD, the real-life performance impact is very low. Better still, HMB is not resource-hungry. Most HMB SSDs use only 64MB of system RAM, which is next to nothing even on older PCs.
Let's use the WD Blue SN5100, a PCIe 4.0 SSD that not only lacks a DRAM cache but also uses slower QLC flash , as an example. If you go through TechPowerUp's review of said SSD , you can see that, even though it lacks a DRAM cache and uses QLC memory, the only metric where it noticeably falls behind top-of-the-line PCIe 4.0 SSDs is sustained write performance, where it drops to a measly 400MB/s once its SLC cache fills up. In every other test, it's near the top, battling it out with drives that pack dedicated DRAM caches and TLC memory, and cost more.
You can freely use such an SSD as your system drive
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As you've just seen, DRAMless drives with HMB support are a perfectly fine choice for virtually any scenario, even as boot drives. As long as they feature HMB and a solid controller, the only penalty you might face is a couple of extra seconds of boot time.
I can personally attest that HBM drives work well as boot drives. None of the handheld PCs I've tested so far has included DRAM drives. Every single one comes with HMB drives, and during my testing, I've never encountered any OS-related or game-loading issues.
Further, none of the handheld PCs I use on a daily basis (a Steam Deck, an ASUS ROG Xbox Ally X, and an ASUS ROG Ally X) have a dedicated DRAM cache; they all use HMB and work just fine. I've never had any performance-related issues stemming from the storage drives, even though I've used these machines for much more than just gaming.
QLC SSDs are generally a less-than-ideal choice, even when they support HMB
Micron
Now, while the WD Blue SN5100, an HMB-only QLC SSD I used as an example of a well-performing DRAMless drive, performs as well as DRAM SSDs, it's still a less-than-ideal choice for certain use cases, given it packs QLC flash.
The two areas where QLC drives lag noticeably behind their TLC cousins are sustained write performance and write endurance represented by the TBW or "Terabytes Written" metric . The first isn't that important for most people, since you can usually write hundreds of gigabytes of data at once before the write speed falls off a cliff. But low write endurance, which is usually half or less of what TLC drives offer, can be an issue.
If you plan to use the drive for write-heavy workloads such as photo and video editing, working with large databases, and most server-related workloads, it's best to get a drive with high write endurance since it'll have a much longer lifespan. While an SSD won't suddenly die when it reaches its TBW limit (manufacturers are quite conservative regarding the official TBW numbers), it might start developing various issues (slower performance, missing or corrupted data, and so on).
Patrick Campanale / How-To Geek
While OS-related workloads are mostly read-heavy, QLC SSDs aren't the best choice as boot drives either. Not only because you want your system drive to be as durable as possible, but also because QLC drives become much slower when filled up , much more so than TLC drives. This can not only negatively impact boot times but also the overall snapiness of the system as well as application installation and startup times.
While QLC drives with HMB are a fine choice for storage drives and read-heavy use, you should opt for TCL SSDs with HMB if you need a drive with high write endurance, or plan to use it as a boot drive.
To find out whether a particular SSD comes with DRAM, HMB, or no cache whatsoever, you can check out its specs page on the vendor's website or read SSD reviews. I recommend Tom's Hardware and TechPowerUp , both of which offer excellent, in-depth SSD reviews. To quickly find the specs of a specific drive, visit Tom's Hardware's SSD Hierarchy table and TechPowerUp's SSD Specs Database .
Instead of focusing on drives with a dedicated DRAM cache, you can opt for an HMB SSD, which can often save you a nice chunk of change. HMB drives are usually more affordable than DRAM-equipped ones while not being much slower.
What you should look for is a decent memory controller and flash chips, solid thermal performance—i.e., that the drive in question won't thermally throttle during light or medium workloads—competitive price, and high write endurance.
