USB Drives - How do they Work?

USB, which stands for Universal Serial Bus, is an industry standard that was adopted in the 1990s. The USB flash drive, since it first went on the market in the early 2000s, has become ubiquitous due to its affordability. But how does it work and what do they mean for data recovery?

Also known as a thumb drive, pen drive or USB stick, USB flash drives are rewritable and removable, and now reach capacities of up to 1TB thanks to their utilisation of NAND flash memory. A crucial goal in the development of NAND flash technology has been to reduce the cost-per-bit and increase chip capacity, with the end goal of flash memory rivalling traditional hard disk drives. They do, however, present new challenges in terms of data recovery. 

There are two types of memory – volatile and non-volatile. Volatile memory is temporary; once the power supply is cut off, the data disappears. This is how data is stored on hard disk drives, which use moving parts to read data stored magnetically on a platter. This is why hard drives emit noise and vibrations, and why they’re more susceptible to physical damage. Non-volatile means the information stored on the chip will not disappear if there is no power supply. It’s non-volatile memory, or semipermanent, that is used to store data on a USB flash drive. Flash memory is transistor-based, and non-volatile; it has no moving parts, and any information stored on the NAND chip remains there semi-permanently i.e. until it is deleted or formatted.

The average USB flash drive is made up of several components, including a USB plug to act as the interface to the host device, a storage controller, a crystal oscillator for controlling the data output of the device, and a NAND flash memory chip for storing data. Perhaps one of the greatest benefits of USB flash drives is their plug-and-play nature; the driver that supports the drive instructs the port to query the flash drive as soon as it’s plugged in, and a command sent to perform a read request. To write data to the NAND chip, the file is converted to a binary format, which is sent to the USB port for forwarding it to the flash drive’s NAND chip.

The main difference between hard disk drives (HDDs) and flash chips found in USB flash drives is the lack of moving parts, and the reduced risk of physical damage in the latter because of this. There is also a difference in the way flash drives writes and stores data; hard disk drives write data to platters in a linear fashion, to sectors of a standard size. USB flash drives, on the other hand, spread the individual pieces of data that form files all over the chip, and can be found in several locations because of this. This can make data recovery quite tricky.