What is flash storage?

Flash storage, once considered an expensive alternative to traditional storage solutions like HDDs, has taken centre stage in recent years as lowered prices have made it more accessible.

Flash storage is, simply put, a data storage technology found in computers, smartphones, tablets, cameras, and all-flash arrays that uses flash memory.

With microsecond latency and the ability to keep data without a power source, flash storage is fast and reliable. It’s also versatile, with solutions that can work for both average consumers and enterprises.

How does flash memory work?

Flash memory is made from solid state chips. They have transistors connected to each other so they function like a NAND logic gate. Flash memory is non-volatile; this means it can preserve data even with the power off. Data is stored using a charge much like a capacitor representing a bit. These are inside surface-mounted chips connected to a printed circuit board.

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When flash memory is erased, it's done so in entire blocks rather than individual bits. The drawback of this is that it's slower than RAM and will also wear out faster than it. But flash memory now lasts longer thanks to software techniques such as wear levelling (this arranges data across these blocks so that erasing and rewriting doesn't wear out a single block prematurely).

What are the benefits of flash storage?

Flash memory, unlike traditional hard drives, doesn’t have any moving parts. This makes it more durable and ideal for use in more rugged or easily dropped devices, like a mobile phone. Since a high capacity of storage can be packed in smaller units, flash memory can be stored in compact, lightweight forms like USB drives and camera memory cards.

Flash is also faster than a normal hard drive, with high transferring speeds and the ability to boot up an operating system far more quickly.

Different types of flash storage

Flash storage comes in two architectures: NOR and NAND.

NOR is best known for providing high-speed random data access by connecting memory cells in parallel. James Bore, managing director of tech and security consultancy Bores Group, says this method allows the system to access every cell individually.

Consequently, it’s ideal for computing scenarios where the user needs to access small datasets quickly, like configuration files and executable code. NOR is commonly used in the firmware and bootloaders of embedded technologies like wearables and other small connected devices.

NOR is one of the oldest types of flash storage, tracing its origins back to the early 1980s. Japanese engineer Fujio Masuoka invented NOR in 1984 while working for Toshiba. But it wasn’t until the end of this decade that the technology was commercialized, with Intel launching the world’s first NOR chip in 1988.

NAND is another well-known type of non-volatile memory. It was created by Masuoka in 1987, three years after he invented NOR storage. Brought to market by Toshiba the same year as its creation, NAND works by linking memory cells in a sequence. This makes NAND ideal for storing large datasets. However, as pointed out by Bore, its random data access speeds are slower than NOR.

Because NAND is optimized for high-density storage and is generally considered more cost-effective than NOR, Bore says it’s used in “almost all consumer flash storage devices” found on the market today. These include smartphones, tablets, computers, MP3 players, digital cameras, USB sticks, microSD cards, SSDs, and more.

NAND storage can vary based on the number of bits stored in cells, with the cell acting as a “single transistor”, according to Bore. The main types of NAND storage are single-, multi-, triple--, and quad-level cells. Bore adds that “various voltage levels” are used for storing these bits, pointing out that triple-level cell NAND storage stores three bits but has eight charging levels.

Each type of NAND storage has different performance, endurance, and cost benefits. Generally speaking, the more bits per cell NAND storage has, the greater storage density and affordability it’ll offer. The tradeoffs, though, are reliability and endurance. These factors can affect the use case of the different NAND storage types.

For example, single-level cell NAND storage stores a single bit and offers high endurance, making it suitable for industrial and enterprise applications. But it can be costly. On the other end of the scale, quad-level NAND storage will store four bits in a cell for high-density storage. Its use cases include consumer electronics, data analytics, AI, cloud computing, data archiving, and more. However, it’s not as durable as single-bit NAND storage and therefore wouldn’t be as suitable for some industrial and enterprise environments.

While NAND storage already comes in many different forms, this space is fast-evolving. Penta-level cells are already in development, and Bore says some people in the industry are already talking about the next big thing: hexa-level cells. Another recent development is 3D NAND, which increases the density of flash storage even further by stacking several layers of cells vertically.

All flash versus hybrid

Two common types of storage solutions are all-flash arrays and hybrid flash arrays. But what do they do, and how do they differ?

An all-flash array (AFA) does exactly what it says on the tin: it only contains flash storage, which comes in the form of a solid-state drive (SSD). Compared to traditional hard drives, AFA storage can access data faster, consumes less power, boosts the performance of applications, and lowers latency. Its use cases range from cloud and high-performance computing to data analytics and video editing.

On the other hand, hybrid flash storage uses both SSDs and hard disk drives (HDDs). They’re perfect for those who want a more powerful alternative to traditional HDDs but don’t have the budget for a costly AFA system. Describing hybrid flash as “more cost-effective” than AFA, Bore says they use flash “as a cache to store the most frequently-accessed data”.

What is NVMe?

Non-volatile memory express (NVMe), is a storage access and transport protocol developed specifically for flash storage. It succeeds SATA and SAS protocols, designed for HDDs, and uses the Peripheral Component Interconnect Express (PCIe) physical interface to enable high-speed data transfers between storage devices and computers. In addition to higher performance, NVMe offers lower latency than SATA and SAS.

What are the disadvantages of flash storage?

Despite these benefits, there are still several drawbacks to this storage system you’ll need to consider when weighing your options.

Flash has a limited number of rewrite-erase cycles before individual blocks can no longer be used. The cells will wear out after 10,000-one million erasings. Reading disturbs nearby cells and hence it can not read the same cell too many times, and in some cases you may need a special version of a programme to protect the drive from wearing out prematurely.

Is flash storage getting cheaper?

Flash storage is more expensive than a normal hard drive because it's still a relatively new technology. The spinning platters of metal the make up a traditional hard drive, on the other hand, have been around for decades, allowing the technology to mature and become cheaper as manufacturing processes are finessed.

Although flash storage had been getting cheaper over the years, prices have recently spiked due to surging demand for all-flash arrays in data centers. In April, Tom's Guide reported that flash drives rose between 126-251% year on year, in a surge running roughly parallel to rising RAM prices.

This isn't the first time flash storage prices have fluctuated due to changing market conditions. During the COVID pandemic, when many factories around the world closed to comply with lockdown rules, flash storage manufacturers struggled to access the materials needed for creating flash drives. Shipping was also delayed in this period. Consequently, the cost of flash drives increased by 30%.