The Differences Between Primary & Secondary Memory

Computers use two types of memory to run software programs and store data, just as the human brain uses memory to execute functions and put information away. Some of this memory is used temporarily, while the other kind of memory is permanent. When you create a document in your word processor or even play games on your computer, the internal “brain” of the computer is at work, using both forms of memory.

The primary memory is a computer’s main memory, and the computer will not run without it. When you use a piece of software, the computer uses its primary memory to temporarily store the program’s code and data. The primary memory of a computer is like the working memory of the human brain: The computer processes and stores information from a piece of software at the same time. The information is stored for a limited time, only when it’s needed to execute a software program.

Computers also need secondary memory, which is used to store large amounts of data permanently. Secondary memory is like long-term memory in the human brain. Once the computer needs to keep the data it processes, it goes to a storage device where it can be recalled later. Secondary memory holds information that might not be in use but can be accessed at any time.

Random access memory, most commonly called RAM, is the main type of primary memory. RAM is in use while the computer is turned on, but the contents are erased once the computer is shut off, according to "Rudiments of Computer Science,” by Jay Bhattacharya. Most basic computers have one to four gigabytes, or the measurement of computer data storage equal to 1 billion bytes, of RAM. Primary memory also includes read only memory, or ROM, which stores instructions for booting up the computer or turning it on. Secondary memory devices include hard disks, flash drives, CDs and DVDs. Standard computers have a few hundred gigabytes of secondary memory storage on a hard disk, according to the Teach-ICT website.

Another major distinction between these types of memory is that most primary memory is considered volatile, while secondary memory is nonvolatile. The term "volatile" refers to memory that is lost when the computer is turned off. RAM is an example of volatile memory. ROM, however, is nonvolatile, because the computer reads this information every time it is turned on. Secondary memory is also nonvolatile, because these devices hold their information even after the computer is turned off.