The "Class" number is a measure of sustained transfer rate. Class 4 usually provides better small-block random-write speeds than Class 10, as needed by flashed-based OSs. "Usually" applies to Transcend, SanDisk, Delkin, APG. It does not apply to PNY, Patriot, Kingston, or Adata. The newer UHS-1 (4-bit transfer path) mechanism provides the best of both worlds (Very high sustained-transfer rates AND fast small-block random-write speeds) for devices that support it.
Last edited by armygreen; 02-01-2013 at 03:10 AM..