Secondary storage media

GOOD DAY, students. This is lesson six in our series. In this week’s lesson, we will be looking at secondary storage media. At the end of this lesson, you should be able to compare secondary storage devices based on their capacity, speed and portability. You will also be able to distinguish between at least three secondary storage devices.

SECONDARY/AUXILLARY STORAGE MEDIA BECAME NECESSARY FOR THE FOLLOWING REASONS:

1. Primary storage devices, such as RAM and ROM, are limited in size.

2. Primary storage is temporary or volatile, while secondary storage is permanent.

3. Secondary storage can be used for back-up purposes and future use.

A comparison can be made among the variety of secondary storage devices in respect to their portability, speed and capacity. Let us look at each of these key factors. Storage Capacity – This is referring to the amount of information that a particular storage medium can hold. Large, capacity storage devices are more appreciated and preferred for many sophisticated programs and large databases.

Access Speed – This refers to the average time needed to locate data on a secondary storage device. Access time is measured in milliseconds.

Portability – This refers to the ease and accessibility of a device to transfer information from one computer to another.

Every secondary storage device or medium requires its own drive. Media (singular: medium) are the physical hardware on which a computer keeps data, instructions and information for future use. Examples of such storage medium are diskettes, hard disk, compact disks and tapes. On the other hand, storage devices record and retrieve data, instructions and information to and from storage media.

There are two main ways in which data can be accessed on a secondary storage medium. They can be accessed directly or sequentially. Thus, secondary storage devices can be categorised as: Direct-access storage devices (DASD) Sequential-access storage devices (SASD)

Direct-Access Storage – This is where any data can be accessed without reading any other data items first (randomly). Examples: floppy diskette, flash drive, hard disk drive, CD, etc.

Sequential-Access Storage – This is where all data between the read/write head and the required data has to be passed over before the data can be accessed.

The data/information stored on a secondary storage medium is stored and accessed via a read/write head. A read/write head is a device that reads data from, and writes data on to, a storage media.

TYPES OF STORAGE MEDIA

Floppy diskettes Hard disks Magnetic tape USB flash drive CD-ROM WORM Compact disc recordable (CD-R) Compact disc rewritable (CD-RW) Digital versatile/video disc (DVD) Flash memory Jaz/zip disk Blu-ray

FLOPPY DISKS

This is a removable disk that has a small storage capacity (1.44MB); it is typically used to store documents so they can be used on more than one computer. Diskettes are normally used to store back-up copies of important information (in case the original copy becomes damaged or lost) and to transfer information from one computer to another. This storage device, even though important to learn about, is no longer used.

HARD DISKS/HARD DRIVE

This is normally permanently installed and fixed into the computer. However, there are external hard drives available. A hard drive can access data much more quickly than a floppy disk drive; most important, it can store much more data. For example, some hard drives can hold up to 1TB of data.

MAGNETIC TAPE

A magnetic tape is a tape coated with a magnetic material on which data can be stored. This is a sequential-access storage device that is usually used for back-up purposes. Types of magnetic tapes are cassettes, cartridge and reel.

USB FLASH DRIVE

A USB flash drive is a very small, portable flash memory that plugs into a computer USB port and functions as a portable hard drive. USB flash drives are easy to use as they are small enough to be carried in a pocket and plugged into any computer with a USB drive. They can store up to 64GB of data.

CD-ROM

CD-ROM is an optical disk capable of storing a large amount of data (up to 1GB). The CDROM has replaced the floppy disk as the media for software distribution. This is because it has the storage capacity to hold as much data as 700 floppy disks. Data on this medium can be read but, unlike magnetic disk and tape, cannot be changed (read only).

CD-R & CD-RW

Compact disk recordable and compact disc rewritable are types of CDs that allow data to be written to (stored on) disks. CD-R drives allow users to record information to a CD (compact disc), providing an easy way to archive data or share files. CD-RW discs allow you to write data to the CD multiple times.

DVD

A digital versatile/video disc (DVD) is a type of optical disc technology similar to the CDROM. A DVD holds a minimum of 4.7GB of data, enough for a full-length movie. It is commonly used as a medium for digital representation of movies and other multi-media presentations that combine sound with graphics. It is becoming increasingly popular, as it can store much more data than CD-ROMs. It can store up 17GB of data.

BLU-RAY

Blu-ray disc (BD) was designed to surpass the use of DVDs. Blu-ray discs contain 25GB per layer, with dual layer discs (50GB) being the industry standard for feature-length video discs. Triple-layer discs (100GB) and quadruple layers (128GB) are available for BD-XL re-writer drives. The name blu-ray disc refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs.

Blu-ray discs are used primarily as a medium for video material such as feature films. Besides the hardware specifications, the blu-ray Disc is associated with a set of multimedia formats. Generally, these formats allow for the video and audio to be stored with greater definition than on DVD. Blu-rays are thus popularly used for the storage of high-definition movies.

ZIP/ZAZ DRIVE

This storage medium is similar in nature to the floppy diskette, but its storage capabilities are more in line with the hard disk drive. The files you are backing up will determine whether you use the zip or jaz drive. Zip drives come in sizes of 100, 250 and 750MB; jaz discs can hold up 2GB of data. Both storage media are most suited for back-up purposes.

WORM

WORM discs are non-erasable disks that can offer up to 20GB of storage capacity on a single disk. While WORM discs are very portable, the inability to erase data written to the disc makes this removable storage a favourite for archival purposes, i.e., for storage of historical information.

this removable storage a favourite for archival purposes, i.e., for storage of historical information.

FLASH MEMORY

Flash memory is a non-volatile computer memory that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards and USB flash drives for general storage and transfer of data.

We have come to the end of this lesson. See you next week. Remember, if you fail to prepare, you prepare to fail.