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Backing Storage
The Need for Backing Storage
Computer Memory (RAM) is volatile What does volatile mean (in relation to memory)? ……………………………………
Backing storage allows data to be saved permanently.
RAM is often not large enough to store large data files. Backing storage allows large
quantities of data to be stored.
It is most important that backups are made of important data in case it becomes lost
or damaged. Backups will be saved on a backing storage medium (tape, disc etc)
When data is no longer required it may be archived ... kept in long-term storage.
Exercise : The Need for Backing Storage
Backing storage allows …………………………. quantities of data to be stored,
which ………………………….. be lost when the power is switched off.
Hard disks
One or more hard disks are found in the hard drive which is usually housed inside a
computer. Each drive is built into a sealed unit to prevent contamination by dust and
moisture.
What are the advantages over floppy disks?.....................
Access to data is faster than from floppy disks.
Hard discs store more data than floppy disks.
What size hard discs are common? ………………..
They are more reliable than floppy disks as they have more
protection from dirt.
One disadvantage of a hard disc over floppy disk is that it is not portable - you
cannot carry it round and use it on different computers.
The read-write head floats so close to the disk that a small speck of dust would ruin
the disk. This is why the drives are sealed.
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Backing Storage
Floppy disks
Used for storage on microcomputers.
Usually 3.5 inches in diameter. High density floppy disks can store (how much
data?)………….. of data.
Access to data is quicker/slower (delete incorrect) than from a hard disk.
The data can be protected by opening a small write-protect tab which prevents the
contents of the disk being changed.
Floppy disks are portable and can be used for transferring data or programs from
one microcomputer to another, backing up data from a hard disk.
Floppy disks (and hard disks) have to be formatted before they can be used.
DO NOT...
leave floppy disks in heat (e.g. the
sun) or damp
open the sliding metal thingy. it lets
the dust in!
touch the brown disk inside
The discs are protected by a stiff plastic cover. This has a hole for the read/write
heads which is protected by a sprung metal cover.
Exercise : Floppy discs.
Floppy disks usually store ………………………….. bytes of data. There is a writeprotect tab which prevents the disk being accidentally written onto.
…………………………. do not hold as much data as ……………………….
Access to data is slower on ……………………...
…………………………. are portable - they can be used on different computers.
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Backing Storage
Optical disks
Optical disks are read by using lasers.
CD-ROMs - are read-only disks. They store much
more than floppy disks (what is the typical storage
capacity of a CD-ROM? ……………). Software is
usually sold on CD-ROM
CD-Rs are blank CDs that can be written onto only
once by a CD-writer.
CD-RWs can be written onto and the data can then
be deleted, and the disk re-written.
DVD stands for Digital Versatile Disk. They hold much more data than a CD (what is
the typical storage capacity of a DVD? ……………).
Data may be written onto a DVD using a special DVD writer.
Exercise : Optical disks
CDs are read by ………………………………….. There are a number of different
types :
………………………….. - Data is stored on the CD and can only be read.
………………………….. - Data can be written onto it but only once.
…………………………. - Data can be written, deleted and re-written many times.
DVD stands for …………………………………… and can store much more data than
a CD. Entire movies can be stored on …………………………….
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Backing Storage
Magnetic Tape
Magnetic Tape is now mainly used as a backup medium. It is a cheap medium for
backing up hard discs on both microcomputers and mainframes.
Conventional tape comes in reels up to 4600 feet long.
Magnetic tapes stored in racks.
Access times are slow. It takes a while for a computer
to find data if it is in the middle of a tape.
Tape is also available in cartridges.
Tape cartridges are frequently used for backing up hard discs on microcomputers.
Tape streamers can be scheduled to make backups at night.
Exercise : Magnetic Tape
Magnetic tape is ………………………… medium for storing large amounts of data.
Tape ………………………………………………… may be used to schedule regular
backups of important data.
Access times are ………………………….
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Backing Storage
Removable media
Floppy disks are an example of removable media - they can be removed from one
floppy drive and used in another.
Zip drives use high-capacity, removable Zip disks.
How much data can Zip disks store? …….
A Zip Drive and discs
Jaz drives use removable disks with even
capacity as they contain hard disks.
greater
How much data can Jaz disks store? …….
Both of these disks are useful for high-speed backups of large quantities of data. Jaz
drive and disks.
USB Sticks - portable disks which can be attached to a key-ring. (They plug into a
USB socket on the computer). How much data can USB flash disks store? …….
Zip disks store up to 250Mb of data. This is the equivalent of about
…………………… floppy disks.
Jaz drives store even more - up to …………………. of data.
USB memory sticks may be …………………………….. into a computer.
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