Data Recovery: How Does HDD and SSD work differently?

The underlying difference between a hard disk drive (HDD) and a solid-state drive (SSD) is the storage medium. This defines how they work.

How to Write 1 and 0

HDD stores date on its magnetic platter surface, which is divided into billions of tiny magnetic domains. Each domain can be independently magnetized (1) or demagnetized (0). With binary system, we can store all kinds of data on the HDD.

SSD uses flash memories or DRAMs to store ones and zeros. Most SSD manufacturers choose NAND flash memory over DRAM because NAND is non-volatile, which means data will still be stored in NAND even the power is cut off.

Flash memory works by charging or removing electrons in floating gate transistor cells to represent 0 and 1.

How to Read 1 and 0

If the floating gate is not charged(neutral), a positive charge in the control gate creates a channel in the p-substrate that carries a current from source to drain. If the floating gate is negatively charged, then this charge blocks the current between source and drain. By sensing the current flow, the computer will read 1; otherwise, it will read 0. 

The floating gate is completely surrounded by an isolation layer. This enables the floating gate transistor to be used as non-volatile memory, but also imposes the need to find ways to charge or discharge it.

How to Erase HDD and SSD

Erasing HDD is demagnetized magnetic domains (writing 0), erasing SSD is flushing electrons (writing 1).

This is the basic idea of how SSDs work. SSDs work differently among themselves, depending on the flash memories array designs and different flash memory media.