1.5 SECONDARY (AUXILIARY) MEMORY DEVICES

External Storage/Auxiliary Storage (i.e. Hard Disk, Floppy Disk, CD-ROM, DVD, Zip-Drive, magnetic tape) – provides a place where data can be permanently stored and transferred to and from main memory (RAM).

Secondary memory is also known as auxiliary memory or secondary storage. This is a Non-volatile type memory; it means the stored data and programs do not get lost, even after the computer is switched off. Unlike RAM which looses the contents when the computer is turned off, and ROM, to which it is not possible to add anything new, the auxiliary storage devices allows the computer to record information semi-permanently, so it can be used later by the same computer or another computer. Auxiliary storage devices are also useful in transferring data and programs from one computer to another computer. They can also be used as a back-up storage, which allows back up the valuable information that you are working on. So even if by some accident if your computer crashes and the data in it is unrecoverable, you can restore it from back-ups.

The most important auxiliary storage devices are Hard Disk, Floppy Disk, CD-ROMs, DVD, magnetic tapes, magnetic disks etc.

• Floppy Disk

􀀁 Portable. Usually the A drive on your computer.

􀀁Portable disks means that you can carry with you or can be remove them from disk drive A.

􀀁A standard floppy disk can hold 1.44 MB of data.

Slower to access then hard-disks and has less storage capacity, but they are less expensive and portable.

• Hard Disk/Hard Drive

􀀁 Non-Portable. The hard drive is the primary device that a computer uses to store information.

􀀁 In most of the computers partitioning of hard drive is done and each portion is given a separate drive name. For example a 80GB Hard Disk may be partitioned into four drives C, D, E and G each of 20 GB.

􀀁 Most computers have one hard drive located inside the computer case. If a computer has one hard drive, it is called drive C. If a computer has additional hard drives, they are called drives D, E, F, and so on.

􀀁 The hard drive stores the programs on your computer. When you buy a new program, you must first install in onto your hard drive before you can run it. The hard drive is also called the hard disk, hard disk drive or fixed Introduction to PC disk drive.

􀀁 The size of a Hard Drive is measured in Gigabytes. A 20+ GB hard drive is common for new computers, and the larger the hard drive, the more programs you can store on your computer.

􀀁 A Hard Disk/Hard Drive is shown in Figure 12.

 

• CD-ROM Drive

CD-ROM stands for Compact Disk Read Only Memory. A CD-ROM drive reads information from a compact disk. CD-ROMs are high capacity storage, and like, floppy disks are portable (removable). You cannot write information to a CD-ROM (because it is read only), you can only retrieve information.

However, CD-RW (CD Rewritable) drives are becoming more common, these drives allow you to record data such as music files etc. onto CD-RW disks. You can change the data on CD-RW disks. When you type a letter in MS Word, as you type it is being stored in RAM, when you save the file (either to your floppy disk or your hard disk) you are saving to auxiliary storage. The next time you open your letter, you are retrieving it from the auxiliary storage into memory. Auxiliary storage is considered both an input and an output device.

• Magnetic tape:

Magnetic tape is a magnetically coated strip of plastic on which data can be encoded. Tapes for computers are very similar to the tapes used to store the music. Storing data on tapes is considerably cheaper than storing data on disks. 

Tapes also have larger storage capacities, ranging from a few hundred kilobytes to gigabytes. Magnetic tapes are used for taking backup of the large date from computer system.

The table on next page summarizes the different types of secondary (auxiliary) memory devices:






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