If you’ve been shopping for an SSD or using memory cards for cameras, you’ll probably encounter the term “flash memory.” But what is flash memory and how does it work? We’ll explain.
The Origins of Flash Memory
Flash memory represented a breakthrough because it allowed rapid re-writes and could store data without power. Being solid-state, it used no moving parts, so it was rugged and durable, and it needed less power to operate than conventional magnetic disk solutions. This lower power requirement—and its compact size—made flash memory ideal for portable devices.
According to the Computer History Museum, Flash memory gained its name due to its ability to erase data quickly—in a “flash.” Previous erasable, non-volatile solid-state memory chips (such as EPROMS) took minutes (sometimes up to 20 minutes) to erase before rewriting could occur. It was this speed of writing, erasing, and rewriting that later made flash memory a practical replacement for floppy disks or Zip disks in the form of thumb drives and traditional hard disks in the form of SSDs.
How Does Flash Memory Work?
Flash memory is made up of floating-gate transistors, which store electrons on an insulated gate. The gate is electrically charged to hold the electrons, and this charge can be used to represent data. Flash memory can be erased and rewritten because the electrons can be removed from the floating gate, which resets the transistor to its original state. This is done by sending an electrical charge through the transistor, which releases the electrons from the gate.
Flash memory comes in three basic formats: NOR, NAND (named for types of logic gates), and EEPROM. Today, most flash memory is the NAND kind because it is the least expensive and typically uses less power than the other types.
Types of Flash Memory Cards
Electronics manufacturers use flash memory in a variety of applications, including smartphone storage, USB thumb drives, and solid-state drives (SSDs). SSDs are becoming increasingly popular as a replacement for traditional hard drives. SSDs are faster, more durable, and use less power than spinning-disk hard drives.
Throughout the 1990s and 2000s, regular computer owners most frequently used flash memory in the form of removable flash media cards, often inserted into digital cameras and PDAs. Here are a few forms of major flash media cards—including when they were introduced and their maximum capacities:
- CompactFlash: Introduced in 1994 by SanDisk. Available in capacities up to 512GB, later extended with CF 5.0.
- SmartMedia: Introduced in 1995 by Toshiba. Maximum capacity was 128MB.
- MultiMediaCard (MMC): Introduced in 1997 by SanDisk and Siemens. Available in capacities up to 512GB.
- Memory Stick: Introduced in 1998 by Sony. Available in capacities up to 128MB.
- Secure Digital (SD): Introduced in 1999 by SanDisk. Supports up to 2 GB, extended formats support up to 128 TB theoretical.
- xD-Picture Card: Introduced in 2002 by Olympus and Fujifilm. Available in capacities up to 2GB.
- XQD Card: Introduced in 2011 by Sony. Available in up to 4TB data capacities.
- CFexpress: Introduced in 2017 by CompactFlash Association. Available in capacities up to 4TB.
Several of these media card types have been extended with new standards to support higher capacities over time, such as SDHC, SDXC, and MemoryStick Pro. Some flash media card formats have also shipped in multiple sizes, such as miniSD and microSD, which remain compatible with each other through the use of adapters.
Flash Memory Lifespan
As wonderful 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 fairly large.
According to the SD Association FAQ, the typical lifespan of a consumer SD card is about 10 years. However, this can vary depending on the quality of the card and the conditions under which it is used.
SSDs typically last longer than flash memory cards because they are designed for more intense, continuous usage. When shopping for an SSD, look for a “TBW” number, or “terbabytes written.” A higher number means the drive can tolerate more data written to it over time, and it will generally last longer. If you’re a typical home computer user, you shouldn’t need to worry about an SSD failure from too many writes. But SSDs do fail randomly from time to time, so remember to always keep backups. Stay safe out there!
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