Realistic CFexpress Data Rate

The Transcend 1TB CFexpress 900 Type B card takes advantage of PCIe 4.0 and has an advertised Read speed of 3500 MB/s and 2800 MB/s Write. To assume the device is capable of sustaining this speed throughout its 1TB capacity would be fair, but the reality is quite different.

The ultra fast advertised speed only lasts briefly due to built-in cache. A cache is a much smaller portion of the SSD’s capacity that can sustain very high speeds. So why can’t the entire SSD be made out of cache instead? Price. The suspiciously low $179 cost of this drive is possible because the majority of its space is made of cheaper QLC or Quad-Level Cell technology. Not all consumer level drives have this small of a cache. Samsung’s hyper popular 990 PRO sees a couple of Terabytes before slowing to QLC. Server and Enterprise solid state drives use SLC or Single-Layer Cell for the entire device but they run into tens of thousands of dollars.