What’s the difference between computer memory (RAM) and hard drive storage?

One of the greatest sources of confusion for computer users is the difference between a computer’s memory and its storage space. The confusion is not entirely the users’ fault. Overlapping terminology contributes, as does poor word choice. I’ll try to reduce confusion by differentiating the terms as well as talking about their overlap.

A classic example of this confusion is when a person receives an error message which states something about insufficient memory and the person thinks that they need to delete files from their computer to make more memory available. This is not the right action to take. Taking the error message at its face value, the proper response would be to close applications and files to free up memory. Alternatively, one could buy more memory for the computer. Let’s start to examine these terms.

Computers have two kinds of storage — temporary and permanent. A computer’s memory is used for temporary storage, while a computer’s hard drive is used for permanent storage. Whoever selected the term memory for temporary computer storage did the world a disservice since people tend to permanently store information in our memories. If I asked you to recall your first grade teacher’s name you could, most likely, tell me because that piece of information is stored in your memory, right? This is not how computers use their memory. A computer’s memory is also called RAM which is an acronym for Random Access Memory. A computer’s memory is where information is temporarily stored while it is being accessed or worked on. For example, if I’m updating my resume, then I double-click its icon to open it. This process of opening the file, copies it from its permanent home on the computer’s hard drive (aka hard disk drive or hard disk) into the computer’s memory. Once in memory, I can edit it. If the computer loses electrical power while I am updating my resume, the most recent changes I’d made are lost. This is because the information in a computer’s memory is only kept there while electrical power is supplied. To avoid losing my most recent changes, I need to save the file. The act of saving a file copies it back to the computer’s hard drive. The contents of a hard drive remain intact even if the computer is turned off or it loses electrical power some other way.

A simple analogy I use to help remember these terms is that memory is like your desk’s work space and your hard drive is like a filling cabinet. Your filing cabinet is typically large enough to store hundreds of file folders and thousands of pieces of paper. Your desktop work space is not large enough for all of these file folders and papers.

Both temporary computer storage (memory or RAM) and permanent computer storage (hard drives) are measured in bytes. These days they are measured specifically in gigabytes (GB). If you’d like to learn more about bytes and gigabytes, please read this previous Tech Tip. This overlap in measurement systems contributes to some of the confusion.

In early 2012, a new Mac might be equipped with 4 GB of memory and a hard drive whose storage capacity is 500 GB. The primary reason for this great disparity is cost. Memory, RAM, is much more expensive then hard drive storage space. Here’s a rough comparison. One GB of RAM costs about $8, while 1 GB of hard drive storage space costs about 10 cents. In other words, RAM costs about 8000 as much as hard drive storage space. Wow.

This price differential explains why we can have much more hard drive storage space compared to memory (RAM) storage space, but why do we need both? Why are computers designed this way, constantly copying data back and forth, into memory and then back to the hard drive? The primary reason is that RAM is much faster than hard drive storage space. I don’t have exact numbers, but RAM is thousands, probably tens or hundreds of thousands, times faster than a hard drive. This is true for both mechanical hard drives, which have been used for decades, as well as solid-state drives (SSDs), which are becoming increasingly common. Apple uses SSDs in all iPhones, iPads and MacBook Airs. SSDs are an option in the iMac, at present. To add to the terminology confusion, SSDs are based on Flash Memory technology. Flash memory is a permanent type of storage that’s also used in the storage cards found inside digital cameras and USB flash drives that many of us carry in our pockets or briefcases.

The prevalence of confusion between (temporary) memory and (permanent) hard drive storage space is so great that the occurrences of misuse of these terms is greater than the proper use of these terms. For example, a discussion from January 2012 is about how much memory is enough in an iPhone. The original poster’s question should be how much storage space is sufficient in an iPhone. It’s tough to use these terms correctly when so many others don’t. I feel like a fussbudget grammarian when I correct a person or clarify a person’s question. Now that you have a better understanding, help me out and use the terms properly.

The Computer Language web site also has a good article about the terms computer memory and storage and how and why they get mixed and confused.

Note: Since I’m a strong advocate for everybody backing up their computer’s hard drive, I should point out that hard drives should be thought of as only semi-permanent storage. This is because hard drives fail. Every hard drive will eventually fail. It’s only a matter of time. Drives can fail in a number of ways, so some fail sooner than others. Sometimes they give warning signs and other times they don’t. Consequently, it’s necessary to backup the contents of a hard drive. Ironically, we often backup one hard drive onto another hard drive! In previous Tech Tips, I’ve recommended backing up your data to at least two different drives and having one copy of your data stored in an off-site location.


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