9. Backing Storage: Magnetic Types

Definition: Backing storage devices are hardware that is used to store the programs and data that the computer can access. Unlike RAM (or working) memory the contents of backing storage will not be lost when power to the computer system is turned off.

Backing Storage Devices

There are three types of backing storage hardware we need to know about:

1. Magnetic based drives, for example:-
   1. Hard disk
   2. Floppy Disk
   3. Magnetic tape
2. Optical based drives, for example:-
   1. CD drive (ROM and RW)
   2. DVD drive (RPM and RW)
3. Flash or solid state chip based drives, for example:-
   1. USB drive
   2. SD cards.

 

Storage Media

Storage Media is a term used to describe the different categories of backing storage devices on which software and data is saved. The following sections dealing with hard disks, floppy disks, magnetic tape, CD's, DVD's and flash drives are all examples of different types of backing storage media.

 

Magnetic Drives

1. Hard Disk

• Hard drives consist of stacks of non-removable platters coated with magnetic materials – each with its own read/write head as shown in the photo.
• Hard disk drives are built into desktops and laptops.
• The capacity of a hard disk is measured in gigabytes. It holds much more data than a CD-ROM. The capacity of a CD-ROM is measured in megabytes. To find the capacity of the latest hard drive you should look in the latest computer magazines or search the internet.

 

 

Advantages of Hard disks

Large storage capacity. They read and write data very quickly. They can hold large quantities of data.	Hard disk drives use random/direct access to locate data stored on the disk.
Movie: 15. Hard Disks and Floppy Disks

 

 

 

2. Floppy Disk

Floppy disks are disks of plastic coated in magnetic material and enclosed in a hard plastic case. The read/write area is covered by a sliding metal flap.

Although, they used to be very common, as they were a convenient way of transporting files from one computer to another, they not much used anymore.

 

 

Floppy disks are written to and read from, through the use of separate floppy disk drives.

Floppy disks are less popular than they have been because :-

• They are easily damaged.
• Have a limited storage capacity in that they can only hold 1.44MB. Photos, text documents etc have become too large.

 

 

 

3. Zip Drive or Superdisks

Are very similar to floppy disks. Again they are plastic discs coated with magnetic material. The difference between them is that zip disks can store much more. The one shown stores 100MB and you can get them up to 250MB.

 

 

 

Like Floppy disks, zip disks need a specialised zip drive to read and write to the disk.

 

 

 

4. Magnetic Tape

Made of a long plastic strip coated with magnetic material, tape is mostly used for making backups. It can store lots of data, but this data is slower to access, because of having to wind through to the information you need slows down he access time. This makes it impractical for use as main storage

One great advantage of magnetic tape is its cheapness.

 

 

Magnetic tape uses sequential or serial access to locate data stored on the tape.

 

Movie: 16. Random Versus Serial Access

 

 

 

 

 

What you have to do!

Watch the videos above and in your Word document or your Brain complete the following exercises.

1. Provide three advantages to using hard disks as a backing storage device.

2. Why are floppy disks no longer so widely used?

3. Provide an example of backing storage that uses sequential access to data.

4. Explain the difference between random/direct access and sequential access

 

 

What you should be able to do!

1. Provide four examples of Magnetic Type Backing Storage devices.

2. Explain why hard disks are so popular as a backing storage device.

3. Describe why magnetic tape is used for making backups.

4. Describe the difference between Random Access and Serial Access to the data

 

Continue to 10. Optical Storage: CD's, DVD's etc