If you are one of the few folks who did’t get their natural curiosity stamped out while in school, then you might be wondering “how does SSD work?”or “what’s the point of SSD?”. If that is you, stick around and let’s try to make sense of it all.
One thing that is similar between a SSDs and HDDs is that they are both storage devices. However, unlike HDDs (hard disk drives), SSDs (solid state drives) have no moving parts. That means they have no no magnetic platters, and no head rotating over the platters to read or locate data. Carey Holzman’s video explains the difference simply and clearly.
If that is the case, what exactly is inside an solid state drive and how does it store data? To get an understanding of this, we need to find out about a few components.
1. Flash Controller
The flash controller is the heart and brains of the SSD. It is responsible for interfacing with the host computer and the other components of the SSD. When a host computer wants to send data to the SSD, the flash controller directs the flow of data to ensure its reliable storage and retrieval. It also contains the firmware that manages the SSD and performs background processes such as managing the flash file system, wear leveling, error correction, trim, and garbage collection.
2. Volatile Memory (DRAM Cache)
This is a small amount of memory that is used as temporary storage of data. It is not available in all SSDs. Because it is volatile, it requires power to retain information. Firmware in the controller decides when to flush or move the data from volatile (non-persistent) memory to the non-volatile (persistent) flash memory. In the event of an unexpected power loss, data in the cache could be lost or corrupted unless an effective power failure protection mechanism is available.
3. Non-Volatile NAND Flash Memory
Data is persistently stored in and retrieved from NAND flash memory chips. They are non-volatile because they retain data even when there is no power to the SSD.
NAND Flash Memory Types
NAND flash memory is essentially categorized based on how much information each chip can store.
Single level cell (SLC) stores only one bit of information on each cell.
Multi-level cell (MLC) holds more than one bit of information, though it is commonly associated with two-bit memory.
Triple level (TLC) and quad level (QLC) cells, as the names imply, store three and four bits respectively.
The more bits a cell can hold, the bigger the storage capacity. It is common to think that as more bits are crammed into a cell, error rates also increase, causing reliability and longevity to decrease. However, thanks to major headway in storage technology, people are no longer sticking to conventional labels. Economical options that were once relegated as mediocre choices can now have better performance, longer endurance and greater reliability due to powerful controllers, advanced firmware, robust error correction mechanisms, and meticulously screened components, along with stringent testing, validation and manufacturing practices.