Removeable Memory

• Fields of Study: Information Technology; Computer Engineering; Digital Media

Abstract

Removable memory systems allow the user to store digital data and transfer them between computer systems. Using magnetic, optical, and circuit-based systems, removable memory has evolved throughout the digital age and continues to be widely used, though cloud storage may eventually take its place.

Temporary and Permanent Memory

Computer memory, sometimes called "storage," refers to the hardware used to store both computer instructions and digital data for processing. There are two basic types of computer memory. Volatile memory, including a computer's random access memory (RAM), is stored as electrical signals and so requires power. RAM, sometimes called main memory, is created each time a computer is powered on. It provides rapid access to instructions and data. These are already stored as electrical signals and so do not have to be "read" and converted from another storage medium. Nonvolatile memory is stored physically, such that powering down the computer does not erase the data. Removable memory refers to certain subsets of both of these types of memory. Nonvolatile removable memory involves methods of storage that can be removed or transferred from one computer to another. Volatile removable memory is expansion memory that can be installed on a computer to increase temporary memory capacity. One of the most familiar examples of removable memory is the SIM cards used in some mobile phones. Until recently, most mobile devices used removable memory cards to store user data. The card could be removed and installed on another mobile device, allowing users to transfer personal data between mobile devices.

Magnetic and Optical Storage Media

The earliest forms of computer memory consisted of punch cards that represented digital data physically. The data could then be read and interpreted by a computer. In the 1950s, computer engineers began using magnetic storage. Magnetic storage uses electronic heads to write and read data on a tape or other material coated with a magnetically sensitive substance. The floppy disks that were popular in the 1970s and 1980s for storing data and applications were a form of magnetic storage. In the 1980s, computer scientists developed the first optical storage systems. In these systems, data was stored by making physical marks on a medium coated with a light-sensitive material. A laser could imprint the storage medium with digital data. It could then read the data and translate it into electrical signals that could be interpreted by a computer. Commonly used optical storage media included CD-ROMs and later DVD technology. Blu-ray discs are also examples of optical storage technology. Meanwhile, advances in magnetic storage led to the debut of shingled magnetic recording (SMR) devices. SMR devices can create layers of magnetic data that partially overlap like roof shingles. This gives them vastly increased storage capacity.

Solid-State Storage

Reading and writing on magnetic or optical media requires complex moving parts. For instance, a magnetic or optical disk must be turned and a moving laser or electronic head must be used to read the encoded data. These delicate moving parts are prone to malfunction. To avoid this problem, engineers in the 1980s pioneered the use of self-contained solid-state storage systems in which data could be encoded in the form of electrical signals and circuits.

Among the earliest types of solid-state storage was read-only memory (ROM). This typically refers to a storage system that is built into a computer and cannot be erased or altered by a user. Some modern ROM systems, however, can be altered by the user with specialized tools. A computer's ROM usually contains the basic instructions that the computer needs to function. CD-ROMs are so-called because the information they hold also cannot be changed or erased, although they are not solid-state technology.

In the 1990s, a variety of solid-state removable memory systems were introduced to the consumer market. These included flash memory chips and drives that store data as electrical signals. The popular thumb drives, USB drives, and other memory cards and external drives are solid-state storage media. Engineers have also created multi-level cells (MLC), which can store more digital data in each electrical cell and so provide vast increases in storage capacity.

Clouds and Virtual Computing

Removable media, while still used for many applications, rapidly changed in the twenty-first century due to growth of virtual data storage. Cloud networks let users save data to the web and later retrieve the data using any internet-enabled device. These virtual networks quickly replaced the use of removable storage and external hard drives for maintaining personal and organizational data. In addition, engineers began using virtual networks to increase processing capability by distributing tasks across several different computers. As cloud storage and virtual networks handle more of the storage and processing, removable storage has become less popular for consumers, and data centers have greater need of physical storage. Cloud service providers offer a variety of options in terms of memory space, and while many are free, most offer subscriptions and upgrades that allow both individuals and businesses to purchase additional space according to their needs.

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