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Secondary Storage: Definition, Technology & Devices

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  • 0:00 What Is Secondary Storage?
  • 0:34 Types of Secondary Storage
  • 3:31 Lesson Summary
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Lesson Transcript
Instructor: Jackie Masloff

Jackie has taught computer science and technology courses and has a Master of Education in Curriculum and Instructional Technology

When you use a computer, you need to save your work somewhere within or outside the computer itself so that you can access it afterward. Learn what secondary storage is and about some of those devices that are used to store and retrieve data.

What Is Secondary Storage?

Secondary storage is one of the most valuable assets of the computer. It is storage that's separate from the computer itself, where software and data can be stored on a permanent basis. Secondary storage is necessary because memory, or primary storage, loses its data when a computer is turned off whereas secondary storage does not. Therefore, it is commonly known as non-volatile storage. The data on it stays there until it is deleted or overwritten by the user.

Types of Secondary Storage

Magnetic Storage

The primary storage device for a personal computer is a hard drive, also known as a type of magnetic media. Data is written to a hard drive using magnetism and is read by the computer as a combination of 1s or 0s, depending on whether or not there is a piece of data in a particular location. Data is read from the hard drive by means of a read-write head on a mechanical arm that scans the surface of the disk for the presence or absence of magnetism, or 1s and 0s.

Hard drives are usually found inside a computer. They are composed of platters that are typically 3½ inches in diameter with storage capacities ranging from 60 gigabytes to over 2 terabytes.

Optical Storage

Rather than using magnetic media, optical storage uses microscopic light spots to represent the 1 bit and dark spots to represent the 0 bit. As opposed to hard drives, optical storage devices are a single platter, 4.7 inches in diameter and 0.5 inches thick. Variations in spots are detected by specialized lasers similar to how magnetic storage is read.

There are primarily three types of optical storage devices: CDs or compact discs, DVDs or digital video discs, and BDs or Blu-ray discs. They differ in the amount of data they can hold.

CDs can store about 700 megabytes of data and are most often used these days for distributing software. DVDs hold around 4.7 gigabytes of data used for movies while Blu-ray disks have five times the storage of DVDs and are used primarily for high-definition movies.

Solid State Storage

Solid state storage devices, in the form of flash drives and USB drives, have become very popular these days as a way to transport data from one device to another. They're also quieter during usage and require less energy. These devices store data in durable, erasable, lower-power chips or series of transistors using electrical current to represent the data. A 1 bit is represented by a transistor that accepts electrical current while a 0 bit is represented by one that does not.

Magnetic Tape Storage

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