In computing, a TRIM command allows an operating system to inform a SSD which blocks of data are no longer considered in use and can be wiped internally.
TRIM was introduced soon after SSDs started to become an affordable alternative to traditional hard disks as permanent storage in PCs. Because low-level operation of SSDs differs significantly from traditional hard disks, the typical way in which operating systems handle operations like deletes and formats resulted in unanticipated progressive performance degradation of write operations on SSDs. TRIM enables the SSD to handle garbage collection overhead, that would otherwise significantly slow down future write operations to the involved blocks, in advance.
Mac OS X Lion supports TRIM while for SnowLeopard only the MacBook Air builds do so, this hack enabled SSD TRIM support for Snow Leopard on any Hardware and SSD.