How to buy SSD depends on which parameters? how to measure SSD performance is good or bad?

SSD is the main performance parameters are the following:
Maximum sustained read speed, maximum sustained write speed, seek time, 4KB read and write performance, IOPS performance.
The maximum sustained read and write performance: this should be good to understand, in a nutshell is a large number of copyed copy hard disk can reach the speed of the data.
Seek Time: SSD does not have a mechanical structure, so seek time is very short, generally in about 0.1 milliseconds.
4KB read and write performance: This is the most important parameters of an SSD, no SSD leave this parameter even read and write performance of up to 1G / S are meaningless, 4KB read and write performance directly determines the performance of a SSD, Kingston and other low The price of hard disk where the difference between hard drives with Intel and other high-priced.
IOPS performance: per second read and write (I / O) the number of operations to measure the performance of random access. (X-25V read speed average of more than 180M, for only 99$ a SSD is a very good score).
Other parameters: such as SSD flash memory block read and write cycles / life, as well as whether to support the trim instructions.
Supplementary Trim:
The original mechanical hard disk, writing data, Windows will inform the previous erase the hard drive first, then new data is written to disk. Data is deleted, Windows will only be here to be a marker, indicating that here is nothing, wait until the real data to write again really deleted, and to mark this action will be retained in the disk cache, until the disk idle when re-executed. As a result, the disk needs more time to perform the above operation, the speed will certainly slow down.
When Windows recognizes the SSD and confirm the SSD support Trim, delete data, will inform the hard drive remove instruction only use the Volume Bitmap to remember where the data has been deleted. Volume Bitmap is just a disk snapshot to establish the speed marked for deletion region much faster than the read and write directly to hard disk. This step has already save a large amount of time. And then write the data, the NAND flash memory to save data is pure digital form, can be directly based on the Volume Bitmap to the snapshot has been deleted blocks to write new data without having to spend the time to erase the original data.
The above is the principle and the true role of Trim.
 the article source http://www.pcpartsltd.com/blog/how-to-buy-ssd-depends-on-which-parameters-how-to-measure-ssd-performance-is-good-or-bad/