Primary vs Secondary Storage: What’s the Difference?

Primary vs Secondary Storage: What’s the Difference?

January 10

Data storage is one of several basic, yet vital functions a computer performs. The concept of storage itself is defined by a hierarchy of four levels: primary, secondary, tertiary, and offline. You’re probably most familiar with primary storage and secondary storage, but how well do you know them, really? This post will serve as a primer for those who need an introduction or refresher course. So let’s see how primary vs 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 simply “memory” and can either be classified as 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 is non-volatile because the data is there even after you have turned it off. This enables some applications to recover unsaved information in the event of a crash.

RAM photo

Examples of Primary Storage

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

PROM: Programmable Read Only Memory is an advanced form of ROM that will allow writing data – but only once. Similar to a blank CD or DVD, PROM does not comes with data stored on the chip. But once you have written data to it, you cannot modify or delete that information anymore.

Cache memory: Also known as CPU memory, cache memory stores instructions computer programs frequently call upon during operation for faster access. Since it is physically closer than RAM, this is the first pace the processor looks for instructions. If it 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 CPU, which allows active programs to deliver optimal performance to the end-user. Speed and usefulness aside, the fact that the loss of power means the loss of data makes RAM a short-term storage solution. In fact, it’s lack of long-term viability is the reason it makes sense to save your progress when working in one program or another.

From Primary to Secondary Storage

Despite essentially functioning as opposites, both types of 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 wither overwrite or delete it. So even when you turn off the device, all data is intact on this medium.

Common Examples of Secondary Storage

Hard drives: The hard drive is the face of secondary storage in modern computing. Many computers bundle hard drives as internal storage mediums. But you can also connect them externally via USB or firewire. 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 two or more backup files of everything on different devices for speedy recovery.

Optical 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 in order to store any substantial amount of data. Optical media actually have exceptionable read speeds, capacity, and portability. This is why they are still a viable form of secondary storage today, even if 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. Tape lives inside cassettes and cartridges, and thanks to recent innovations, can store a TB of data or more. There has been much debate regarding its reliability over the years, but tape is still an option for secondary storage and backup across corporate environments worldwide.

Secondary storage is named as such because it doesn’t have direct access to CPU. As a result, it is considerably slower than primary storage. Luckily it compensates for that lack of speed in a number of ways. Aside from offering greater data retention, secondary storage is usually twice as cheap in comparison 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 Last Word

Primary and secondary storage are integral to a comprehensive storage strategy. The former provides reasonably fast and efficient access to resources. The latter offers a long-term retention solution for the swarm of documents, photos, and videos we accumulate on a daily basis. We sometimes take them for granted, but I’m sure we could not imagine the IT landscape without them.