The terms memory and data storage are often confused. Both are means by which a computer keeps data used to perform tasks. As such, both are measured in bytes. However, memory and data storage are two separate entities, and the terms should not be interchanged. Memory is commonly referred to as Random Access Memory (RAM), but also includes Read-Only Memory (ROM). Data storage is also called hard disk space.
The main difference between memory and data storage is their function. Storage is used to hold all the computer’s information. Data stored in the hard disk is permanent and is not lost when the computer is turned off. When a file is deleted, only the access to that file is removed, not the information itself. This is why computer experts are able to restore information onto a computer even though such information has been deleted. To permanently delete a file, the hard disk must be formatted or overwritten. It is even possible that even though a disk has been formatted, an expert can still view the information. There are programs available that write nonsense data over the disk information, making information unreadable to anyone.
Memory, on the other hand, enables the computer to access files from the hard disk quickly. When a computer runs an application such as a word-processor, the central processing unit (CPU) retrieves the data from the hard disk and loads it in the RAM, allowing for quick access. The amount of RAM a computer has limits how many programs can be run at once. Since information stored on RAM is lost when the computer is turned off, saving a file in such an application writes the information to the hard disk so that it is not lost.
ROM is used to store boot firmware, the information the computer uses to start up. The boot firmware tells the computer to check all its systems and hardware and opens the computer's operating system. ROM also contains information that keeps the computer, and its various hardware attachments, working properly. Unlike RAM, information stored in ROM is not lost when the computer is turned off.
Memory and data storage can work together, however. When the computer does not have enough RAM to support its processes, it converts a portion of the hard disk into virtual memory. Virtual memory acts the same way RAM does. However, since it is a part of the hard disk, using virtual memory slows the computer down. A way around this is to add memory to the ailing computer. There are also products known as removable storage, some of which are thumb drives and compact disks (CDs), that allow users to store files and move them from computer to computer.