How do solid state drives work?

Unlike a hard disk drive, solid state drives have no moving parts or spinning platters – hence the name ‘solid state’. Solid state drives, or SSDs as they are more commonly known, use a series of semi-conductor memory chips known as NAND. These chips are specifically designed to retain their charge even when not powered up, making them a type of non-volatile memory. Whilst hard drives rely on magnetic polarity for their binary source code, NAND chips use electrical charge. This electrical charge is read as ‘0’ when not charged and ‘1’ when charged.

The NAND chips in a SSD are organised in a grid which is referred to as a block and rows are known as pages. Individual block sizes can be up to 4Mb in size. Because there are no moving parts SSDs are much faster than HDDs – but is the performance better overall? Although they can read and write data much quicker, overwriting data is much slower. Erasing data can only be done at block level because it involves a high amount of voltage, which would stress cells at a lower level. Therefore overwrite commands must copy the contents of the entire block, erase that block and write the updated data to a new page.

SSDs use data compression algorithms and complex single-bit error correction. Together with the load balancing work, it’s no wonder that SSDs require a much more sophisticated controller than a HDD. With so much NAND memory to ‘control’, the drive controller can be compared to high end data storage RAID arrays.

SSDs typically have 4 or 8 channels. Essentially these are pipelines that move data continuously. Unlike hard drives which only have one channel to move traffic, the controller is able to distribute data amongst many NAND chips simultaneously. The major benefit of SSDs is the speed or data transfer rate. This is measured in megabytes of data moved per second and in some instances can be five times faster than hard drives. If you’re not convinced look at how long a laptop with a traditional hard drive takes to be ready for use. Compare that with a SSD laptop which is so much faster. So, hard drive versus solid state drives. Who wins? In our opinion there is no winner or loser. They both have their advantages and disadvantages. Only the user can decide which best suits their needs.