HD Tach will test the sequential read, random access and interface burst speeds of your attached storage device (hard drive, flash drive, removable drive, etc). All drive technologies such as SCSI, IDE/ATA, 1394, USB, SATA and RAID are supported. Test results from HD Tach can be used to confirm manufacturer specs, analyze your system for proper performance, and compare your performance with others. HD Tach is very easy to use, quick, and presents data in easy to read graphs, including the ability to compare two storage devices on screen at the same time for easy analysis.
Bursts are provided only for your review. SSD's don't cache the same way HDD's do (in many cases they don't cache reads at all), so burst testing typically results in figures that are lower than the sequential throughput figures, unless the controller and flash is of exceptionally low latency. While Samsung and ADATA (Silicon Motion 2246EN) give great figures here, this test data does not directly translate into any particular real world performance result.
HDTach feeds the tested drive a continuous string of small sequential requests. This is a single threaded operation, which means the SSD doesn't get to see what's coming next. The lower the QD=1 latency of the controller pipeline, the better the numbers we see from this test. It doesn't necessarily equate to real-world maximum throughput, as typical file IO occurs at QD>1, but it does mean something for analysis and response times to single infrequent commands, which is why we include these results.
The 850 PRO shines here. Better throughput than any of the competition in this test. Of note is the ability to keep write speeds up near maximum even at the smallest capacity, which appears to lose only 5MB/sec (1%), compared to the other modelswhich show significant falloffs due to their limited die count and flash page write speed.