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HD Tune — Transfer rates
HD Tune lets us present transfer rates in a couple of different ways. Using the benchmark's "full test" setting gives us a good look at performance across the entire drive rather than extrapolating based on a handful of sample points.

RAPID mode doesn't improve the 840 EVO's read performance in HD Tune, but it definitely speeds up writes. The extra caching layer pushes the SSD's average write speed to 420MB/s—a 6% improvement. The RAPID config actually starts the write speed test at 665MB/s, but the burst is short-lived; performance quickly falls and levels off.

Note that the standard 840 EVO config has a slightly higher write rate for the first portion of the test. I suspect that's a benefit of the drive's flash-based TurboWrite cache.

HD Tune runs on unpartitioned drives, with no file system in place, so it may not be an ideal candidate for RAPID's caching intelligence. For another take on sequential speed, we'll turn to CrystalDiskMark, which runs on partitioned drives. We used the benchmark's sequential test with the default 1GB transfer size and randomized data.

When Samsung first demonstrated RAPID mode to the press, it used CrystalDiskMark. No wonder. The 840 EVO's sequential transfer rates more than double when the DRAM-based caching scheme is enabled.

Interestingly, the first run in the read test registered only 536 MB/s. RAPID mode only kicked reads into high gear for subsequent runs, which all clocked in around 1150 MB/s. Writes were through the roof right off the bat, though.