The Tech Report: "The 840 Series offers solid performance at extremely affordable prices. It does have a weakness, though. The drive's TLC NAND costs less per gigabyte than the MLC flash typically used in consumer SSDs, but its write performance is somewhat compromised by the higher bit density.
Samsung has attempted to address that shortcoming with its next-generation successor to the 840 Series. The 840 EVO features a faster controller, newer TLC NAND, and a dedicated write cache populated with speedier SLC flash. There's a second layer of caching that leans on system memory, too.
Despite these enhancements, the 840 EVO retains the budget-friendly pricing of its predecessor. We've been testing one pretty much around the clock for the past few days. Let's see how it stacks up."