What are HDDs and SDDs,

Solid state drives work by using electronic circuits to store and retrieve data. Data is stored in “blocks,” and these blocks can only be written fully once. To keep sequential data together and response times low, the block must be completely erased and rewritten on a different block. Unfortunately, the blocks are not durable and are damaged in the process of erasing. The writing/erasing is how wear occurs on an SSD and is why most SSDs come with integrated “wear-leveling” technology, which evenly distributes the wear out and extends the lifespan of the device.

Some of the electronic circuits in an SSD are NAND (“Not AND” logic gate) flash memory that consists of non-volatile NAND transistors. Non-volatile NAND transistors store data as a charge in semiconductors on silicon memory chips arrayed and sometimes stacked on circuit boards. The stacks are called 3D NAND and boast far greater storage capacities because memory cells are stacked on top of one another. Single-level cells (SLC) are the most expensive — but most durable — variety of SSD technology. Adding an additional bit of storage space per cell reduces costs accordingly and every additional bit stored is denoted differently, starting with multi-level cells (MLC), triple-level cells (TLC) and finally quad-level cells (QLC).