Secondary storage device
- FLOPPY DISK
- HARD DISK
- MAGNETIC TAPE
- OPTICAL DISK
- PUNCHED CARDS
- PAPER TAPE
- Memory cards
- Smart cards
Primary memory(RAM of the computer is of volatile nature. Therefore, secondary memory
is required. Some of the secondary storage devices are:
FLOPPY DISK
A floppy disk is a thin magnetic coated disk contained in a legible or semi-rigid protective jacket. Data is stored in tracks and sectors.The copy disks ar usually 3.5″ in size. However, older oppy disks may be in use; these would be5.25” in size. Double-sided high density3.5″ disks can hold 1.44 Mb of data.
Once data is stored on a floppy disk it can be written protected by clicking a tab on the disk. This prevents any new data from being stored or any old data is erased.
Advantages/disadvantages:
- They are easily physically damaged if unprotected and magnetic fields can damage the data.
- They are relatively slow to access because loppy disks rotate far more slowly than hard disks, at only six revolutions per second, and only start spinning when requested. The access speed is about 36 KB per second.
HARD DISK
The hard disk is a direct-access storage medium with a rigid magnetic disk. The data is stored as magnetized spots arranged in concentric circles (tracks) on the disk. Each track is divided into sectors. High data rates demand that the disk rotates data at high speed (about 3,600 pm). As the disk note, read-write heads move to the coat rack.
The disk is sealed and lubricated and the head hovers on a cushion of air just above the disk to avoid damage. These are therefore called floating heads. The storage capacity of the hard disk can be Gigabytes(GB), ie. thousands of Megabytes (10Mb, information
Advantages:
- Very fast access to data. Data can be read directly from any part of the hard disk (random access). The access speed is about 100 KB per second.
Extra information:
- Data s stored by magnetizing the surface of flat, circular plates called platters which constantly rotate at a high speed (typically 60 to 120 revolutions per second). A read/write head floats on a cushion of air a fraction of a millimeter above the surface of the disk. The drive is inside a sealed unit because even a speck of dust could cause the heads to crash.
- Programs and data are held on the disk n blocks formed by tracks and sectors.
- For a drive to read data from a disk, the read/write head must move in or out to align with the correct track this is called the seek time). Then it must wait until the correct sector approaches the head.
MAGNETIC TAPE
A recording medium consisting of a thin tape with a coating of fine magnetic material is used for recording analogue or digital data. Data is stored in frames across the width of the tape. The frames are grouped into blocks or records which are separated from other blocks by gaps. Magnetic tape is a serial access medium, similar to an audio cassette, and so data (like the songs
on a music tape) cannot be quickly located.
However large amounts of information can be stored within the magnetic tape. This characteristic has prompted its use in the regular backing up of hard disks.
Adv advantages/disadvantages:
- Accessing data is very slow and you cannot go directly to an item of data on the tape as you can with a disk Itis necessary to start at the beginning of the tape and search for the data as the tape goes past the heads (serial access.
- Magnetic tape is relatively cheap and tape cassettes can store very large quantities of data (typically 26GB).
- Extainfomaion:
- Just like the tape in a tape recorder, the data is written to or read from the tape as it passes the magnetic heads.
OPTICAL DISK
An optical disk is impressed with a series of spiral pits in a flat surface. A master disk is burnt by high-intensity laser beams in bit patterns from which subsequent copies are formed which can be read optically by laser. The optical disk is a random access storage medium; information can be easily read from
any point on the disk. A standard CD-ROM can store up to 650Mbof data, with 14,500 tracks
per inch (TPI).
CD-ROM stands for Compact Disk- Read Only Memory, It is now possible to have CD-ROMs where extra tracks of information can be written onto them by the user. These are called read/writable CD-ROMs and these are becoming a popular and cheap method for storage.
CDs are available in 3 formats:
CD-ROM’s- ROM means Read Only Memory and this means you can only read from the disc, not write or store data onto it. This is the most common sort of CD available and is the way most software programs are now sold.
Like a floppy disk. a CD-ROM only starts spinning when requested and it has to spin up to the correct speed each time it is accessed. It is much faster to access than a floppy but it is currently slower than a hard disk(a modern 40x speed CD-ROM drive is 40 times faster than the 15 KB per second of the original single-speed CD-ROMs)
PUNCHED CARDS & PAPER TAPE
These are media which were popular in the past but their use required large storage space and was time-consuming. With the development of hard disks and other storage devices, their use
has practically disappeared.
This multiple-choice section willask10 questions to test your knowledge and total your score. You will be given the opportunity to try the quiz again once you have finished all the questions.
OTHER MAGNETICsTORAGE MEDiA:
- Zip and Jaz dives are similar to loppy drives because the individual disks are removable and portable but they hold much larger amounts of data (typically between 100 MB and 2 GB).
OTHER OPTICAL STORAGE MEDIA
Digital Versatile Disc DVD):
- DVD drives are now replacing CD drives in computers due to the huge memory capacity of the disk and the high quality of stored images. A DVD single-sided, single-layer DVD can store up to4.7GBof data, the equivalent of 26CD-ROMS. This means fl-motion films with soundtracks and subtitles in multiple languages can easily be stored on one DVD disk.
- Afim stored on a DVD has significant advantages over magnetic VHS videotape because the digital images and soundtracks are of a higher quality and do not deteriorate with constant use. The user can also move to any part of the film immediately (random access).
- Multi-layer and double-sided DVDs can hold up to 17GB of data.
- DVD-RW drives (writable drives) are still quite expensive but may eventually replace home CD systems and VHS tapes as a way of recording films and music.
- RECORDABLE COMPACT DISK MEDIA
CD-R-these CDsare initially blank but you can use a special read/write CD drive unit to store programs and data onto the disc but they can only be written once.
CD-RW -these are similar to the R’type above but you can read, write and delete files
from the disc many times, just like a hard disk.
Both CD-ROMs and CD-Rs can be referred to as wORM devices. This stands for
Write Once Read Many times.
OTHER WAYS DATA CAN BE STORED:
Magnetic strips-a stip of magnetic tape built into a plastic card can store a small amount of data Phone cards, debit cards, and library cards can be written to so changes in the data can be stored.
Smart cards- a processing microchip built into an anaplastic card can store data as well as process information. The SIM card used in mobile phones stores phone numbers and names
as well as allowing providing a menu of options and allowing you to connect to your service provider.
Memory cards- there are used in a wide range of applications to store data. Typical Examples include Compac FlashTM and SmartmediaTM memory cards which are used in digital
cameras. They can have a capacity of over 512 MB and a memory card reader or floppy disk adapter can be used to transfer the data to a computer.
ROM (Read Only Memory)- chips are used to store the permanent operating system
data of the BIOs,. Some types of computers, such as a pocketbook, may be used to store major programs such as a word processors. They are however mo:e difficult to replace when a
new version is released. They are also used to store the permanent programming inside a domestic
device such as a television or washing machine.
