Flash memory is also evolving, but there are still only four main manufacturers of flash: Micron (who is also responsible for Intel flash), Toshiba, Samsung and Sandisk. Micron makes flash memory according to the ONFI standard, but Toshiba, Samsung and Sandisk make so-called ToggleFlash. These are typically faster, but actual SSD performance is decided by the combination of controller and flash chips.
The most important development was made with the Samsung 840 (not Pro) SSDs. As far as we know these are the first to transtion from MLC chips to TLC chips. Each memory cell can store three bits, compared to the two bits for MLC chips. This means that the same storage capacity only takes of two-thirds of the chip's surface.
TLC makes further price decreases possible in the future, but there's also a flipside. It is generally known that TLC chips can be overwritten much less frequently than the traditional MLC chips. Cells in MLC chips can be overwritten about 3,000 times before they are unable to process new data. For TLC chips that limit is reportedly around 750 times. Wear-leveling algorithms make it so all cells are used equally often in order to maximise the lifespan, but 750 times is obviously reached much sooner than 3,000 times. We made some calculations which indicate that typical consumer use won't be impacted by this limitation. However, people that use their PC intensively or for professional purposes should probably stick with MLC SSDs for the time being.
Less than 128 or 256 GB?
Most SSDs have capacities of 128 GB or 256 GB. Keep in mind that, like manufacturers of conventional hard drives, for SSD companies 1 GB equals 1000x1000x1000 bytes and not 1024x1024x1024 bytes. The results is that a 128 GB SSD in Windows only has 119 actual gigabytes available, and for a 256 GB model that's 238 actual gigabytes. The about 7 percent difference is used for over-provisioning, or extra memory cells that can be used when other cells fail or in order to decrease the load on the other cells.
Many of the SandForce-based SSDs have 120 GB or 240 GB, which translates to 112 and 224 of actual GB in Windows. It's a fail-safe measure that allows a complete chip to break without losing any data. You could describe it as RAID 5 with flash chips.
The new Samsung 840 with TLC memory has 120 GB instead of 128 GB and 250 GB instead of 256 GB. This leaves extra room for overprovisioning, to compensate for the shorter lifespan of TLC memory.