Following up to our review of the 1TB mSATA EVO, we have the smallest capacity size available from this new product group: the 120GB model. If you've followed SSDs for the last few years, you already know that smaller capacity drives write slower than larger models. For those that don't already know, let's cover why.
When the SSD controller reads and writes to flash, it does so through channels. You can think of the controllers channels to the flash as roads to a stadium (controller), from the suburbs (NAND flash). The more roads you have coming in, the faster people can get to the stadium and sit down. In SSD terms this is called parallelism; more data comes to the controller through more channels, since the bus width is fixed. Smaller SSDs have less NAND packages, so there are not as many roads to carry the data.
The Samsung 840 EVO 120GB mSATA has just two NAND flash packages, with four-19nm die inside each package. Samsung rates the sequential performance at 540 MB/s read, and 410 MB/s write. Random IOPS performance listed for the 120GB capacity size is 94K read, and 35K write.
To achieve the high sequential write performance using TLC flash, Samsung uses an SLC like layer to cache writes. On the 1TB model, we observed a large SLC area due to the special area being on die, and the larger 1TB model has significantly more die than the 120GB model. What that means is that you have less of a cushion with the 120GB drive that we're looking at today. It's something we'll keep an eye on while during the testing phase of this review.
Looking at the spec sheet, we see Samsung's four new mSATA form factor drives that range in capacity from 120GB, to 1TB. The capacity sizes double at each higher capacity product SKU. The MSRPs are close to that of the EVO 2.5" models: 120GB ($149.99), 250GB ($259.99), 500GB ($489.99), and 1TB ($859.99). We suspect the MSRP prices will fall rapidly to get in line with the 2.5" models. The EVO mSATA models carry the same three-year warranty that the 2.5" models ship with in America.