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HD Tune — Random access times
In addition to letting us test transfer rates, HD Tune can measure random access times. We've tested with four transfer sizes and presented all the results in a couple of line graphs. We've also busted out the 4KB and 1MB transfers sizes into bar graphs that should be easier to read without the presence of the mechanical drive.

Don't try to differentiate between the SSDs in the line graphs. Those graphs are meant to illustrate the massive gap in access times between solid-state and mechanical storage.

The gulf between the SSDs and our lone hard drive works out to multiple orders of magnitude. This vast difference in access times is what makes solid-state drives feel so much more responsive than their mechanical counterparts.

Among the SSDs, the results are very close. Most of the drives are separated by tiny fractions of a millisecond. The Samsung 840 EVO scores better than its siblings in both tests, but you'd be hard-pressed to feel the difference in the real world.

HD Tune's random write speed test produces similar results. The SSDs are evenly matched, and the mechanical drive is nowhere close.

The Samsung 840 EVO has the quickest 1MB random write response time of the lot, likely thanks to its TurboWrite cache. Not even the high-end 840 Pro can match the EVO in that test. At least the Pro comes close, though. The standard 840 Series lags well behind the top contenders and is nearly 2X slower than its replacement.