The memory/interface controller proved to be a major factor in determining each SSD's performance. Three of the drives we tested use a SandForce SF-2281 controller: the Kingston HyperX 3K, the SanDisk Extreme, and the Intel Series 335 (the controller firmware on this drive is tweaked to Intel's specifications). OCZ's Vector and Vertex 4 drives both use OCZ's proprietary IndiLinx controllers, namely the Everest 2 in the Vertex 4 and the Barefoot 3 in the Vector. Corsair is blazing a path with its Neutron series drives (the GTX and Neutron) by using Link A Media's LM87800 controller. Samsung's 840 Pro utilizes the company's proprietary MDX controller.
As you'll see in our performance chart, drives with the IndiLinx, Link A Media, and Samsung MDX controllers boasted significantly faster write speeds than the SandForce-based competition. In fact, counterintuitively, each of the five drives using those controllers wrote faster than they read. The SandForce-based drives were all good readers, but their comparatively slower write speeds dragged down their overall scores.
On the next page, I'll discuss memory types, interfaces, and how we measured performance.
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.