When purchasing solid-state drives (SSDs)， we often encounter the terms “with cache” and “without cache.” Traditionally， SSDs with onboard cache were perceived to offer superior performance at a higher price， while cache-less SSDs were more affordable but might compromise on speed. However， the advent of Host Memory Buffer (HMB) technology has significantly disrupted this paradigm， enabling cache-less SSDs to achieve enhanced performance and deliver a better user experience.
To fully appreciate the value of HMB， it’s essential to understand two distinct concepts of caching within SSDs. The first is DRAM cache， which serves to store the Flash Translation Layer (FTL) mapping table. The second is SLC Cache， which boosts write performance by emulating faster SLC NAND with TLC or QLC NAND flash. The DRAM cache acts as the SSD’s navigation system， enabling the controller to swiftly locate data. Without it， the controller is forced to frequently access the slower NAND flash to consult the mapping table， leading to increased latency and reduced performance.
Traditional cache-less SSDs store all mapping tables within the NAND flash， inherently limiting their performance. HMB， or Host Memory Buffer， ingeniously utilizes a portion of the system’s main memory as cache via the PCIe interface. This allows cache-less SSDs to achieve performance levels comparable to those with onboard DRAM. Typically， an SSD will allocate about 64MB of system memory for HMB， so users need not worry about a significant impact on their overall RAM capacity. This approach effectively bridges the performance gap previously associated with cache-less designs.
Upon system startup， the SSD requests a portion of system memory to store its FTL mapping table. When the controller needs to access data， it can retrieve this information directly from system memory through the high-speed PCIe channel. This mechanism substantially reduces access latency， proving particularly beneficial in scenarios involving small file random read/write operations， where performance gains can be quite noticeable.
When comparing HMB and traditional cache-less solutions， SSDs with onboard DRAM cache still hold an edge in absolute performance. The dedicated onboard DRAM cache ensures more stable performance， especially under high workload conditions. This is a crucial differentiator for professional applications and heavy multitasking environments where consistent speed is paramount.
In practical everyday use， most average users will find it difficult to discern a significant difference between an HMB SSD and one with onboard cache. Unless one is engaged in massive file transfers or running highly demanding professional applications， the HMB solution is more than adequate for the vast majority of tasks. In essence， HMB technology strikes an excellent balance between performance and cost-effectiveness for SSDs.
However， it’s important to note the limitations of HMB. Typically， SSDs connected via USB bridges， such as external portable SSDs， cannot utilize HMB technology. This is due to architectural differences and the nature of USB interfaces in managing host-device communication.
Furthermore， for scenarios where data integrity is of utmost importance， HMB SSDs may not be the ideal choice. A notable incident occurred in August of this year when Microsoft’s KB5063878 update caused data loss on a small number of HMB SSDs， with no possibility of recovery. Such a severe data loss warrants caution， and users with critical data should consider disabling automatic system updates or opting for traditional cache-equipped SSDs if data security is their primary concern.
For the majority of average users and gamers， HMB SSDs represent the most cost-effective option. Everyday computing， office applications， and game loading do not place extreme demands on SSD performance， and HMB capabilities are perfectly sufficient for these tasks. This allows gamers to enjoy large capacities and high speeds at a more accessible price point. Additionally， HMB SSDs are a recommended choice for users of thin and light laptops， as the absence of onboard cache translates to lower power consumption and reduced heat generation， which is highly advantageous for portable devices.
For content creators and professional users who frequently handle large file transfers or run demanding high-performance applications， SSDs with onboard cache remain the more suitable choice due to their superior sustained performance under heavy loads.
