Primary Storage vs Secondary Storage: What's the Difference?

January 25th, 2023

Data storage is one of several elementary yet vital functions in our digital world. Data storage is defined by a hierarchy of four levels: primary storage, secondary storage, tertiary storage, and offline. You’re probably most familiar with primary storage and secondary storage, but what do you really know about them? This post will serve as a primer for those who need an introduction or refresher course. So let’s take a look at how primary storage and secondary storage square off in the complex storage landscape.

The Main Storage Option

Typically located inside the computer, primary storage temporarily houses applications and data currently in use. Primary storage is often referred to as “memory” and is classified as either volatile or non-volatile. Volatile memory such as RAM loses data as soon as the device loses power. The flash memory in solid-state drives (SSDs) is non-volatile because the data remains in storage even after you have turned it off. That lets some applications recover unsaved information in the event of a crash.

Examples of Primary Storage


Unlike RAM, Read Only Memory (ROM) delivers both non-volatile and permanent primary storage. ROM retains its contents even if the device loses power. You cannot change the data on it, you can only read it. ROM is a more reliable form of storage, and it will often boot instructions and other mission-critical data.


Programmable Read Only Memory is an advanced form of ROM that allows data to be written—but only once. Similar to a blank CD or DVD, PROM does not come with data stored on the chip. But once you have written data to it, it cannot be modified or deleted.

Cache Memory

Also known as CPU memory, cache memory stores instructions that computer programs frequently call upon for faster access during operations. Since it is physically closer to the processor than RAM, it is the first place the CPU looks for instructions. If the CPU finds the data it needs here, the processor can bypass the more time-consuming process of reading RAM or other storage devices.

Primary storage provides fast access to the CPU. That allows active programs to deliver optimal performance to the end-user. Speed and usefulness aside, the loss of power means the loss of data. That makes RAM a short-term storage solution. In fact, its lack of long-term viability is the driving force behind the saying “save often.”

From Primary Storage to Secondary Storage

Despite their different purposes, primary storage and secondary storage often work together to create ideal storage conditions. For instance, when you save your work in Word, the file data moves from primary storage to a secondary storage device for long-term retention. Likewise, a primary storage device retrieves data from a secondary source to speed up access.

Also known as auxiliary storage, secondary storage retains data until you either overwrite or delete it. So even when you turn off the device, all data remains intact.

Common Examples of Secondary Storage

Hard Drives

The hard drive is the secondary storage standard in modern computing. Many computers bundle hard drives as internal storage mediums, and today hard drives can include spinning disks and solid-state drives (SSDs). System administrators will often create redundant arrays out of multiple hard disks to prevent accidental data loss. To absolutely make sure data weathers the storm, they will keep backup files of everything on different devices in multiple locations for a certain, speedy recovery.

Optica Media

CDs and DVDs are the most well-known members in the class of optical storage. These mediums are the more efficient successors of the 3.5-inch disk drives. You had to use these in spades to store any substantial amount of data. Optical media have exceptionable read speeds, capacity, and portability. That’s why they are still in use as secondary storage to some degree today, even as better options have come along.

Magnetic Tape

In use for well over half a century, magnetic tape was once the very foundation of backup systems. Reel-to-reel tapes have evolved into high-capacity tape cartridges, boasting exceptional durability that continues to earn them a place in over half of today’s hybrid data center. Tape is an affordable option for secondary storage and by enabling longer retention periods and reducing storage requirements.

Secondary storage is named as such because it doesn't have direct access to the CPU. As a result, it is considerably slower than primary storage. Luckily it compensates for that lack of speed in several ways. Aside from offering greater data retention, secondary storage is usually twice as cheap compared to its primary counterpart. It can also store significantly more information. An 8GB stick of RAM is a decent size, while new computers generally have 1TB hard drives. There is no comparison on capacity.

The Cloud: The Best of Both Worlds

The cloud has quickly become the secondary storage medium of choice for many organizations.  But with today’s faster connections, the availability of microservices and other technology advances, the cloud is now used more and more frequently as both primary and secondary storage. How your organization uses the cloud depends on many factors that we’ll cover in a future post. Cloud storage’s most apparent benefits are security and availability. With data stored in the cloud, you can expect your data to always be safe and accessible from anywhere.


Primary and secondary storage is integral to a comprehensive storage strategy. The former provides fast and efficient access to resources. The latter offers a long-term retention solution for the massive amount of data—documents, photos, videos, and so on—that we accumulate continuously. We sometimes take storage for granted, but the IT landscape could not function without them.

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