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What is Non-Volatile Memory? | Definition & Different Types

Updated on October 7, 2013

What is Non-Volatile Memory?


Non-Volatile Computer Memory: Examples & Comparison vs Volatile

Non-volatile memory might sound like a bizarre science fiction term to some, but it's actually something that you very likely use every day. In fact, unless you printed this article off, you're probably using it right now.

It's actually not even a terribly new concept, and it has been in use for many decades to keep our information safe and sound. There are hundreds of different formats, but there are a few that we use a lot these days, and there's new technology on the way. Very exciting!

I've written this article to help answer the question 'what is non-volatile memory?', and I'm going to give a description of what it is, how it works, and go over several examples of the most common uses today. I'll also touch on some up and coming tech that's going to make things even better.

Examples of "Volatile" Memory?

Volatile memory, often called 'temporary memory', is a short term storage solution that most devices still use. You can think of it like a chalkboard: you do your work, but at the end of the day it is erased if not saved.

By far the most recognizable example of volatile memory is RAM, which is used by your computer as you use it. When you 'save' your work, it's transferred from the RAM to whatever storage you use, usually HDD or SSD memory.

Volatile memory storage is usually terminated when it loses its power source, or shortly thereafter.

OK, so what is non-volatile memory?

Non-volatile (also known as 'nonvolatile') memory is pretty simple to understand. Basically, it's a type of computer storage that remains stored even when the power source is shut down.

That means you can return to whatever you were working on before without having to start from scratch. Practically speaking, that means it's something we use every day, many times a day, and it is something we're becoming more dependant on.

Non-volatile memory is often known as 'secondary storage' because (in the way we use it now), we typically have to 'save' our work, transferring it from random access memory (RAM) into non-volatile form.

So why do we use RAM at all? RAM boasts an incredibly high data transfer rate. That means that when we input data (say, from our keyboard), it is written to memory almost instantly. If we were to use traditional non-volatile memory for our working set, your computer would run much, much slower.

Because of that, a non-volatile memory system is often set up to be used whenever data is 'saved', and thus transferred from RAM to long term storage.


Different Types of Non-Volatile Memory: Examples

This type of storage is found in dozens of forms throughout history, probably hundreds if we looked closely. Here are a few of the most common types you might be familiar with.

Punch Cards: It might seem funny, but punch cards are a type of non-volatile computer memory storage. Think about it: when the program is written, the set of instructions are 'coded' into the card physically. Obviously this is one of the least dense forms of information, and not very practical.

Hard Disk Drives (HDD): Most computers boast one of these, and they're an example of a non-volatile memory storage device that's widespread. It uses a rapidly rotating disc that's coated with a magnetic material. Data is stored in 1s and 0s, but it can be accessed randomly and put back together. They're not super durable, but they do retain data without a power source, and they're cheap, effective and have about the best storage density out there (currently).

Compact Discs, DVDs, Blue-Ray Discs: CDs are often associated with music storage, and they're not as commonly used for computer uses anymore. DVDs, on the other hand, are commonplace and used for storing computer program data and movies. Blue-Ray discs have even more storage space and are used for high definition movies. All three are related to hard disc drives in that they are coated with a magnetic material and written by a separate recorder. They suffer from degradation over time, but they're an inexpensive form of non-volatile memory that's very popular still.

And if you're wondering, yes, those old cassette tapes in your vehicle glove box count as non-volatile memory too!

Solid State Drives (SSD): The SSD is a very popular form of non-volatile computer memory, and it's on the upswing for practical reasons. It's more expensive than the standard HDD memory, but they boast great speed, incredible informational density and low power requirements, plus they are durable because there are no moving parts (unlike a HDD).

The most common form of SSD is NAND-based flash memory, and it's commonly found in USB thumb drives. You'll also typically find flash memory in your phone and MP3 player. Data is stored in individual cells arranged in many columns and rows, and thus it's stored even when the power is shut off.

Phase Change Memory is Coming: Look Out Flash!

There are a few exciting new technologies on their way. Holographic memory looks incredibly promising in a Star Trek sort of way, but it seems a long way off.

One of the coolest new forms of non-volatile memory storage is Phase Change Memory, or PCM, and it's just around the corner. Well actually it's already here.

So What Is Phase Change Memory?

OK, PCM is a new type of non-volatile memory storage that takes advantage of a substance called chalcogenide glass, which has some curious attributes that we've taken advantage of.

In particular, chalcogenide glass reacts to heat and changes from a crystalline to an 'amorphous' state. When it's in these different states, it has a drastically different electrical resistance, meaning that it can be used to store information. Newer versions of this technology are working to change the state by merely hitting it with a laser pulse.

OK, enough of the mumbo jumbo. PCM memory storage is potentially a lot quicker than flash. It can be written faster due to the fact that entire blocks of data must be erased with SSD memory, but PCM can rewrite individual bits.

It can also store a lot more data in a smaller amount of space, potentially enabling it to be around half the size of SSD memory systems (which are already pretty darn small).


There are a few. PCM memory is a technology still in development. It's susceptible to temperature, and the production methods haven't been ironed out yet, so it's expensive to produce. That being said, Nokia has already produced a phone taking advantage of PCM storage, and more are on the way.

I would expect PCM to start hitting the market around 2016. Initially it will probably be fairly high-priced, but that will come down as they get better at producing it. Be prepared to see some truly tiny devices with this new non-volatile memory storage solution!

Memory Poll:

What type of memory does your computer hard drive use?

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