When introducing the new Xserve Nehalem, Apple unveiled that in addition to the (only) 3 SATA or SAS HD, one could also add a SSD; a feature that a reader from XLR8Yourmac decided to investigate.
If the information was in fact available, we did not initially spotted it. This SSD offering 128 GB is in fact a 1.8" HD model in SATA Flex format, the same (exotic) format used in MacBook Air. If you are already thinking of getting one to upgrade your MacBook Air, you might think twice: performance levels are lower than other (cheaper) models, and it costs 500 USD. this is another example of the weird choice made by Apple from time to time why not having a SATA port for adding high performance SATA SSDs?