Even With SATA 3Gb/s, An SSD Makes Sense
If you go by the synthetic benchmarks most reviewers like to run (stuff like AS-SSD, CrystalDiskMark, PCMark 7, and Iometer), then a 6 Gb/s SATA connection appears imperative for getting the most out of today's drives. In certain cases where you're pushing a ton of data sequentially, that's absolutely the case. However, those same tests aren't very good at conveying the "feel" of a machine recently upgraded from conventional to solid-state storage. Moreover, they make it look like you really need a modern platform to take advantage of a modern SSD. Our real-world metrics demonstrate that those theoretical differences aren't always practical, though. In most cases, a SATA 3Gb/s-attached Samsung 840 Pro is almost as fast as the same drive connected to a 6 Gb/s link.
Almost No Advantages for SATA 6 Gb/s On A Typical Desktop
The 840 Pro soared in our synthetic tests when we had it hooked up to a 6 Gb/s port. It also fell flat several times when we hamstrung it using SATA 3Gb/s. When we specifically targeted sequential reads and writes, along with random I/O at high queue depths, the differences were especially pronounced. But once we started through our handful of real-world tasks, booting up and shutting down Windows 8, and loading a number of applications, the differences shrank to almost nothing. The deltas we did measure wouldn't be perceptible during your day-to-day grind.
Because the synthetic benchmarks deliberately push workloads designed to flesh out the differences between extremely-fast devices, but are seldom seen in a desktop environment, they don't correlate to the more common tasks you perform. Random I/O is important to measure, but there's a fair chance that you'll never see a queue depth of 32. And while we enjoy clocking peak sequential transfer rates like quarter-mile drag races, it's pretty uncommon to move large media files between two storage devices that wouldn't bottleneck each other. If you do copy an ISO, for example, from one SSD to another, you'll get a nice boost from SATA 6Gb/s connectivity. But if you're moving the same file from an SSD to a conventional disk, the fastest interface in the world won't help overcome the spinning media's limitations.
The Three Most Important Things: I/O, I/O, and I/O
Random I/O performance is very important from a practical point of view. Under Windows, most I/O operations occur at low queue depths. In such a situation, our synthetic benchmarks show us that there's not much difference between SATA 6Gb/s and 3Gb/s. There’s barely even a theoretical performance gap at a queue depth of one, and certainly no practical difference.
We can now answer the question of whether you need available SATA 6Gb/s ports to justify an SSD upgrade. Clearly, you're still going to see plenty of benefit from solid-state storage, even if you're using a 3 Gb/s connector. In the real world, a 3 Gb/s interface doesn't bottleneck common applications. It's only when you push the technology's limits using synthetic benchmarks, server/workstation-oriented workloads, or large SSD-to-SSD transfers that 6 Gb/s signaling kicks into gear.
The real key is getting an SSD into your machine. Just have a look at what happens when our 840 Pro goes up against the fastest desktop hard drive we've ever benchmarked, Western Digital's ValociRaptor. The disk didn't stand a chance in any of our synthetic or real-world tests.