External and Internal Storage Devices: Optical, Magnetic & Semiconductor Storage

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  1. 0:05 Introduction
  2. 0:25 Magnetic Storage
  3. 2:55 Optical Storage
  4. 4:03 Semiconductor
  5. 5:10 Cloud
  6. 6:29 Lesson Summary
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Taught by

Lori Jacobson

Lori holds an MBA. She has taught business and accounting at several community colleges.

Let's explore the capacity of internal and external storage devices. We'll learn how optical, magnetic and semiconductor storage works, as well as identify some examples of storage devices.

What Type of Storage Do You Use?

What type of storage do you use for saving your computer work? The hard drive only? A USB drive? Do you watch movies on DVD or Blu-ray? There are many different storage methods for computers and other technology. We'll describe each of the categories of devices they fall under, the general mechanics of each and their physical characteristics.

Magnetic Storage

There are three main categories of storage devices: optical, magnetic and semiconductor. The earliest of these was the magnetic device. Computer systems began with magnetic storage in the form of tapes (yes, just like a cassette or video tape). These graduated to the hard disk drive and then to a floppy disk. All magnetic media use the same general process of a read/write head magnetizing material. On a hard drive, the materials are magnetized on a glass or aluminum disk. Early storage was small. It would take many tapes to back up a mainframe system - a large system with few programs and many users - and many floppies were needed to back up significant work on a personal computer because of the low storage capacity. In the stone age of personal computers, all programs, and the work accomplished using them, were stored on 5 1/4-inch floppy disks. The storage capacity of that floppy was typically only for text and was 360 kilobytes (KB). Consider a two-page, text-only, double-spaced document is about 15 kilobytes. There was a significant period of time where the 3 1/2-inch floppy disk dominated the market. The 3 1/2-inch floppy held 1.44 megabytes (MB) of data, or roughly 750 text-only pages (750 pages is about a ream and a half of paper).

Floppy disks were an improvement on earlier magnetic storage devices.
Floppy Disk Image

Magnetic media transitions were made to larger-capacity portable disks such as the ZIP drive. These started with 100 MB sizes and moved to 250 and 500 MB. Part of the trouble with the ZIP drive was the speed with which they developed - it was so fast that the manufacturer neglected to keep backward compatibility going. In other words, the drive hardware for the 250-MB ZIP wouldn't work for the 100 MB disk, and the 250 disk couldn't be used in the 100. We've moved light years beyond that to improved internally mounted hard drives, which can hold out at least a terabyte of information. Think of a terabyte as enough different music to listen to while working a full-time job for an entire year! And these same hard drives have become portable and lightweight enough to carry around with us, giving us the ability to bring software and data files everywhere we go.

The original magnetic media became cumbersome. Not all machines had ZIP drives installed, and frequently, a document or database large in size took up several floppies. I remember backing up an accounting system on a personal computer in the early 1990s. It took more than a dozen floppies to back up one company's data!

Optical Storage

About that time, optical devices were starting to be marketed. An optical storage device is written and read with a laser. It is strong and can handle temperature fluctuations much better than magnetic media. Because the floppy was so inexpensive at this time, it took several years before the optical drives became affordable to the general and small business consumer.

Optical storage devices read data using a laser.
Optical Storage Device

The disks used for storage (like CDs, DVDs and Blu-rays) were more expensive than floppies but held a lot of data. A compact disc (CD) can hold 700 MB of data, or roughly a little over an hour of music. It actually took until CD players became common in homes and cars for the playing of music for CDs to come down in price enough for more use by consumers. Digital video discs (DVDs) began being issued for consumer-released movies. A single-sided DVD holds 4.7 gigabytes (GB) of data, so a normal, not overly-computerized two-hour movie will fit. A movie that is heavily supplemented by technology, such as The Fellowship of the Ring, takes two full DVDs (or both sides of a DVD).


The third device, a semiconductor, has been around for a very long time. The chip, made primarily of silicon, receives a charge to hold the data. Some uses of semiconductor technology that may surprise you are flash drives (also known as thumb drives or plug 'n play), personal digital assistants, mp3 players, cell phones and digital cameras.

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