Flash SSD Tech Talk
There are two types of Flash memory: NOR and NAND. NOR provides an external address bus and can thus be directly addressed by storage controllers. Hence, it is possible to directly execute code from NOR flash memory, making it the proper choice for firmware applications. However, NOR also does not feature bad block management mechanisms. NAND flash can only be accessed in larger blocks, which are organized in so-called pages, in order to boost throughput. Thanks to this layout, the number of connections is smaller than with NOR. Also, NAND memory oftentimes comes with an integrated controller, which takes care of bad block management and wear leveling algorithms. This allows manufacturers to sell NAND Flash even if a few bad blocks are available. While this sounds like a disadvantage, it is actually an advantage for higher capacity storage, as it allows for production yields to be significantly increased and keeps flash memory prices low for current and upcoming memory densities.
But there is one more difference between flash memory devices, as flash cells can be designed to store either one or multiple bits. Single-level cell flash (SLC) stores a single voltage level, while multi-level cell flash (MLC) can store at least two bits. SLC chips hence are significantly faster and more energy efficient than their MLC brothers, and they typically sustain more write cycles than what MLC offers, although this should not be an issue for desktop users anymore.
Manufacturers typically don’t break down the technical details about what kind of flash memory that they offer in their data sheets for flash SSDs, although we think it would be good to know these specifics for a particular product. At the same time we have to emphasize that it’s impossible to assess or even estimate a flash SSD’s performance by only looking at the technical specifications. While manufacturers should be straightforward with throughput numbers and these are mostly reliable, a 2.5” Flash SSD’s throughput can vary between 25 MB/s and 115 MB/s (like Memoright’s SSDs).
Most flash SSDs were designed for 2.5” or 1.8” form factors, as flash-based hard drive are mostly interesting for mobile use given their robustness and lower power consumption. Also, the lower capacities of 16-128 GB can be sufficient in laptops, but hardly for desktop PCs. Should you still want to use a 2.5” Flash SSD in a desktop environment, then it would be easy to purchase a frame to install the 2.5” drive into a 3.5” bay. Western Digital has also gone down this road with its latest enthusiast-class hard drive, the VelociRaptor, which is a 2.5” hard drive at 10,000 RPM that is shipped with a 3.5” frame to cool the drive and allow installation in conventional desktop environments.
Lastly, flash drives provide a larger temperature range and better robustness for industrial applications. While hard drives may be operated at 5-55°C with few exceptions, most flash drives sustain temperatures of 70°C and industrial-grade drives can handle temperature ranges of -40°C to 85°C, which will work for car infotainment solutions geared for polar or desert climate zones.
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