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What is the difference between memory and storage?

Storage and memory each fulfill a connected but separate role in a computer, based mostly on whether or not the data each uses stays in place when the power is turned off.

Both memory and storage are terms used to refer to internal storage space on a computer. Memory, usually referred to as random access memory (RAM), is where an application loads its data during processing by the CPU, while a storage drive is where data is stored for long- or short-term retention.

The storage drive was traditionally a hard disk drive (HDD), but solid-state drives (SSDs) made up of flash memory modules have become increasingly popular. System memory, or RAM, is faster than storage but usually more expensive on a per-megabyte basis than, say, a MB or gigabyte of disk storage space.

The line between memory and storage blurs paging, also known as swap space, where a portion of the storage drive is turned into memory for the computer to swap out applications and data from active memory to the drive. In this way, the storage drive becomes active memory, which, while slower than the RAM in the system, can be used to create larger virtual memory spaces for systems. Most systems will create a swap or paging space that is equal to two times the actual RAM space on a computer.

A computer system also includes read-only memory, which keeps files such as system firmware or BIOS programs that are only read in ROM. You can update the information in this kind of memory in a process called flashing, but otherwise, it can only be read, not written to, by the computer system. Other types of memory can act like storage drives for everything from MP3 and picture files to presentations and other data. These formats include USB flash drives, CompactFlash cards or memory sticks. They all serve basically the same purpose, storing data but not applications.

types of memory

One important difference between memory and storage is the state of the data when the system is turned off. Most RAM is volatile, which means the data is lost when the system is turned off. Storage devices are usually nonvolatile, so they retain data when the system is turned off. Both the spinning magnetic disk in an HDD and the flash modules in an SSD are a type of nonvolatile memory and are therefore able to retain data even without power.

The future of memory and storage is fuzzy

The line between active memory and storage is getting closer to not just blurring, as in paging, but disappearing altogether. Manufacturers are working on technologies that promise to combine the speed of RAM with the ability of flash to be nonvolatile memory.

Optane SSD
The 3D XPoint-based Optane SSD from Intel

Among these technologies are ferroelectric RAM and magnetoresistive RAM, but the one closest to achieving the goal of being both active memory and storage is phase-change memory (PCM). Intel and Micron Technology Inc. developed a technology they call 3D XPoint based on PCM, and Intel has already placed storage devices on the market under its brand name, Optane. Intel Optane memory modules work with a small number of manufacturers and motherboards as cache memory to increase read and write performance to a storage device.

This was last published in October 2018

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How does your organization decide on the right mix of technologies for data storage and memory?
More hard drive storage allows to store more things on your computer. However, it hardly affects computers performance.
A badly fragmented hard drive will seriously affect a machines performance.  The more that it has to hunt for the data stored on it the slower it will run.  This is very evident it what used to known as the swap file.
Remember that the memory is gone when the system is powered down. The storage remains until it is deleted. Memory can be cleared manually while the system is active by ending applications that may be running that are not needed. 
From my vista, the 3D XPoint NVDIMM blurs the line. Also NVDIMM-N