Memory

Although the controller plays a big role in determining an SSD’s performance, the type of flash memory inside an SSD is also a huge factor. The SSDs in this roundup used either synchronous or toggle-mode NAND.

You might also encounter the terms SLC (single-level cell), MLC (multi-level cell), and TLC (triple-level cell) when researching SSDs. An SLC NAND cell has two states—on or off—so it can store one bit of data. An MLC NAND cell has two states besides off, so it can store two bits of data, while a TLC NAND cell has three states in addition to off and is therefore capable of storing three bits of data.

While MLC and TLC NAND deliver more capacity in the same physical space, they also bring a trade-off in performance and endurance. SLC NAND is faster and more durable than the other two types, but it’s also more expensive; you’ll find it today only in enterprise-level drives. Very few drives use TLC NAND, because it’s not as durable—it can’t handle as many program/erase cycles (which I’ll explain in a moment) as SLC and MLC can. Each of the drives in this roundup uses MLC NAND.

A note about endurance: All types of NAND flash memory have a limited life span. The MLC memory in consumer SSDs is good for 3000 to 10,000 P/E (program/erase) cycles, which is enough to deliver several years of normal usage. Unlike a mechanical hard drive, an SSD cannot simply write (program) data on top of old data that’s no longer needed; once flash memory has been written to, it must be erased before it can be written to again. Newer SSDs running on modern operating systems (including Windows 7, Windows 8, Mac OS X 10.6.8, and Linux kernel 2.6.28) use the TRIM command (it’s not an acronym, despite the caps) to actively inform the SSD controller of memory cells that contain unneeded data, so the controller can proactively erase those cells and make them available for storage once again.

So how long should you expect an SSD to last? The manufacturers’ warranties provide a clue: Both of OCZ’s drives, Corsair’s Neutron drives, and Samsung's 840 Pro drives carry a five-year warranty; the rest of the drives we reviewed are warrantied for three years.

Interface

To take full advantage of a state-of-the-art SSD (that is, one with a third-generation SATA 6-gbps interface), and get close to the speeds you'll see in our benchmark charts, you’ll need a motherboard with a third-generation SATA 6-gbps interface.

While mechanical hard drives don’t come close to saturating the second-generation SATA 3-gbps bus, the latest SSDs are already bumping up the against the limit of third-gen SATA. If you're adding an SSD to a laptop that has only a SATA 3-gbps interface, save yourself some money and go middle of the road—you’ll get very little benefit out of connecting a SATA 6-gbps drive to the older interface. If you're upgrading to an SSD on a desktop that has only a SATA 3-gbps interface, buy either a SATA 6-gbps controller card or a SATA 6-gbps piggyback card, such as the Apricorn Velocity Solo x2 (read our review). Under any circumstance, buy a top performer, and in the future you can transfer it into a better system to realize its full potential.

Performance

We evaluated the SSDs with a series of real-world data-transfer tests (by "real world," we mean a commonplace selection of data). Each drive was required to read and write both a 10GB mix of smaller files and folders and a single large 10GB file. To see just how fast the drives could go, we utilized a 16GB RAM disk to avoid any bottlenecks or interaction issues that a hard drive or second SSD might cause.

Our test bed consisted of an Asus P8Z77-V Pro/Thunderbolt motherboard, an Intel Core i7-2600K CPU, and 32GB of Corsair Vengeance 1600MHz DDR3 memory. The operating system was Microsoft Windows 8 (64-bit).

When it came to reading data, every drive we tested turned in good numbers. Oddly enough, the 256MB OCZ Vertex 4, which took fourth place overall with its combined reading and writing, was the slowest reader at 393.5 MBps (file mix and large file combined). The highest combined mark, on the other hand, wasn’t tremendously higher: Samsung's 240GB 840 Pro delivered 450.8 MBps (about 14 percent faster).

Overall, the aforementioned Samsung 840 Pro and OCZ's 256MB Vector were the stars of the roundup, finishing first and second respectively. The 840 Pro delivered an overall combined read/write speed of 496.2 MBps, and the Vector delivered 489.1 MBps. The 840 Pro finished first in every test except for writing our mix of smaller files and folders, where the Vector bested it. The Corsair Neutron GTX (240GB) placed third with a speed of 459.1 MBps, the OCZ Vertex 4 took fourth place at 449.4 MBps, and the 240GB Corsair Neutron finished a rather distant fifth at 414.3 MBps.

The Kingston HyperX was the most capable of the SandForce-based drives, posting a combined read/write rate of 407 MBps. The 240GB SanDisk Extreme finished next at 385.8 MBps, followed by the 240GB Intel 335 Series at 368.4 MBps.

To establish a baseline, we also tested an older SSD (a 90GB Corsair Force Series 3) and two mechanical hard drives: Seagate's Barracuda 7200.12 and Western Digital's VelociRaptor, both of which offer capacity that no current SSD can match: 1TB. The WD VelociRaptor is a very fast enterprise-class hard drive that spins its platters at 10,000 rpm. Note, however, that the Corsair and Seagate products do not represent the respective manufacturers' latest and greatest technology; we selected them as representative of the boot drives that consumers might be upgrading from. The Seagate 7200.12, for instance, has half as much cache as the newer 7200.14 model with the same total capacity. And the Corsair drive uses slower asynchronous NAND paired with a SandForce 2200 controller that predates the SandForce 2281 used in the newer drives we reviewed.

The Corsair Force Series 3 SSD managed an overall read/write rate of only 190.7 MBps. Seagate’s 7200-rpm hard drive delivered 117.7 MBps, while the VelociRaptor achieved 213 MBps. In plain language, the bargain SSD smoked the Seagate hard drive, but it couldn't keep pace with the VelociRaptor.

On the next page (scroll down past product-reviews for the link), I'll tackle the issue of pricing, bundles, and the bottom line.