How were flash drives invented

What is the technical difference between a flash drive and an SSD?


I just read a question about backup using flash drives, but I wasn't sure why SSDs are better for backups than flash drives.

Solid-state drives look like larger versions of flash drives to me. But surely there has to be something that makes the former much more reliable than the latter.

What is the difference between an SSD and a regular flash drive? For example, are they both using NAND?




Reply:


Both flash and SSD are based on a NAND-based flash memory that stores data without electricity and can therefore be referred to as flash memory.

Technologically, the main differences between the two are:

  1. The underlying technology for building the NAND,
  2. The quality of the flash memory controller,
  3. The computer connection: USB or SATA.

NAND technologies

NAND technologies differ in two ways: speed and price.

On the one hand there is MLC (Multi-Level Cell), a storage element that can store more than a single bit of information. Most MLC NAND flash memories have four possible states per cell (or even more in the case of TLC), so that several bits of information can be stored per cell. This reduces the number of transistors required, thereby reducing size and manufacturing cost, while reducing speed and increasing the possibility of errors.

On the other hand, there is SLC (Single Level Cell), where each cell can exist in one of two states and stores one bit of information per cell. This increases the access speed and at the same time increases the manufacturing cost and power consumption.

An MLC cell is typically rated 10,000 erase / write cycles, while an SLC cell may last ten times longer than it did before failure.

Because of these differences, MLC is typically used in slower and cheaper media that is usually accessed via USB. A good SSD uses SLC and, while more expensive, is faster, has a longer lifespan, and is usually accessible via SATA 2 or 3.

Storage controller

A USB mass storage device only has a small microcontroller with little on-chip ROM and RAM.

An SSD controller is much more complicated. The controller is an embedded processor that executes code at the firmware level and is one of the most important factors in SSD performance. Some of the functions performed by the controller include:

  • Error Correction Code (ECC)
  • Bear leveling
  • Bad block allocation
  • Read scrubbing and read incident management
  • Read and write caching
  • Garbage collection
  • Encryption

With a hybrid SSD, the controller also manages a small, classic hard drive.

Interconnects

A flash stick typically uses a standard A-USB connector that provides the physical interface to the host computer. These can now be increased to USB-3 speed for the more expensive models or to USB-2 speed for the more common models.

SSD technology uses electronic interfaces that are compatible with conventional internal hard disk drives with block input / output (I / O). In addition, new I / O interfaces such as SATA Express have been developed to meet the specific requirements of SSD technology. Most SSD cards tend to be much faster than traditional hard drives.

Summary

A flash stick usually has less storage capacity, is slower, cheaper and also less reliable than an SSD.

Of course, there are always devices that bridge these differences through the use of compensation technologies.

References:







  • Most SSDs use NAND, although better ones may use faster memories like DRAM.
  • I think one of the biggest differences is simply that SSD drives are of a higher standard than USB flash drives. Flash drives are typically used for data transport and short-term storage. So they don't have to be as reliable as an SSD.











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