What is flash memory?


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If you’re buying an SSD or using memory cards for your cameras, you’re likely to come across the term “flash memory”. But what is flash memory and how does it work? We will explain.

Origins of flash memory

In the early 1980s, a group of Toshiba engineers led by Dr. Fujio Masuoka invented a new type of non-volatile semiconductor memory called flash memory.

Flash memory represented a breakthrough as it allowed data to be quickly overwritten and could store data without power. Being solid state, it did not use moving parts, so it was strong and durable, and required less power to operate than conventional magnetic disk solutions. This lower power consumption and compact size have made flash memory ideal for portable devices.

According to the Computer History Museum, flash memory gets its name from its ability to quickly erase data—in a flash. Previous erasable non-volatile solid-state memory chips (such as EPROMS) required minutes (sometimes up to 20 minutes) to be erased before overwriting could occur. It was this speed of writing, erasing, and rewriting that later made flash memory a practical replacement for floppy or Zip drives in the form of flash drives and traditional hard drives in the form of solid state drives.

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How does flash memory work?

Flash memory is made up of floating gate transistors that store electrons on an insulated gate. The gate is electrically charged to hold electrons and this charge can be used to represent data. Flash memory can be erased and overwritten because electrons can be removed from the floating gate, which resets the transistor to its original state. This is done by applying an electrical charge through a transistor, which releases electrons from the gate.

Diagram or scheme illustration in blue

Flash memory comes in three main formats: NOR, NAND (named after the type of logic gates) and EEPROM. Most flash memory today is of the NAND type because it is the least expensive and usually consumes less power than other types.

Types of flash memory cards

Various types of flash memory cards
Various types of flash memory cards. Benj Edwards

Electronics manufacturers use flash memory in a variety of applications, including smartphone memory, USB flash drives, and solid state drives (SSDs). SSDs are becoming increasingly popular as replacements for traditional hard drives. Solid state drives are faster, more reliable, and consume less power than spinning platter hard drives.

Throughout the 1990s and 2000s, flash memory was most commonly used by ordinary computer owners in the form of removable flash memory cards, which were often inserted into digital cameras and PDAs. Here are a few basic forms of flash cards, including when they were introduced and their maximum capacity:

  • Compact Flash: Introduced in 1994 by SanDisk. Capacities up to 512 GB are available, later expanded with CF 5.0.
  • SmartMedia: Introduced in 1995 by Toshiba. The maximum capacity was 128 MB.
  • Multimedia card (MMC): Introduced in 1997 by SanDisk and Siemens. Capacities up to 512 GB are available.
  • Memory card: Introduced in 1998 by Sony. Capacities up to 128 MB are available.
  • Secure Digital (SD): Introduced in 1999 by SanDisk. Supports up to 2GB, extended formats theoretically support up to 128TB.
  • xD image map: Introduced in 2002 by Olympus and Fujifilm. Capacities up to 2 GB are available.
  • XQD map: Introduced by Sony in 2011. Data capacities up to 4 TB are available.
  • cfexpress: Introduced in 2017 by the CompactFlash Association. Capacities up to 4 TB are available.

Some of these types of memory cards have been extended with new standards to support higher capacities over time, such as SDHC, SDXC, and MemoryStick Pro. Some flash card formats also come in several sizes, such as miniSD and microSD, which remain compatible with each other through the use of adapters.

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Flash memory life

As great as flash memory is, it doesn’t have an unlimited lifespan. In fact, it can only be written to a certain number of times before it fails. However, in modern flash devices, the number of write cycles is quite large.

According to the SD Association FAQ, the typical lifespan of a consumer SD card is about 10 years. However, this may vary depending on the quality of the card and the conditions in which it is used.

Solid state drives generally last longer than flash memory cards because they are designed for more continuous use. When buying an SSD, look for the number “TBW” or “terabytes written”. A higher number means the drive can handle more data being written to it over time, and will generally last longer. If you’re a typical home computer user, you don’t need to worry about SSD crashing due to too many writes. But SSDs do fail randomly from time to time, so remember to always keep backups. Stay safe there!

RELATED: What does “TBW” mean for SSDs?

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