Storage Devices
Primary storage: is the storage provided
by memory in a computer system
e.g. ROM/RAM.
Secondary storage: is storage provided
by peripheral devices other than memory
Storage Devices
Secondary storage: is required in a computer
system for three reasons
1. The content of memory is usually volatile, which
means that if power is disconnected the data is
lost.
2. The capacity in megabytes of memory is limited.
3. Memory is more expensive than secondary
storage.
Storage Devices
Several types of disks may be used for
Secondary storage.
• Floppy disks
• Hard disks
• Optical disks (including CD-ROM, writeable
CD, DVD
• Backup Storage Devices e.g. tape
Storage Devices
Floppy Disk
A floppy disk is a low capacity disk which may be
removed from the computer.
There are two types:
Those holding a small amount of data (typically
1.44 Mb
And ‘Super floppies’ known as ZIP disks (typically
100 Mb
Storage Devices
Floppy Disk
They are small lightweight and easy to transport.
Ideal for backups of small amounts of data or for
transfer of data from one machine to another.
Floppy Drives are common to most if not all
computers.
On the down side, they may be easily misplaced,
damaged or stolen.
There is a risk of transferring VIRUSES
Floppy Disk/Diskette
Floppy Disk Drive
Storage Devices
Hard Disk
A hard disk is a higher capacity medium, with up to
hundreds of gigabytes.
They are usually non-removable, but removable
hard disks are becoming more common.
They can be both read from and written to, and are
the standard medium for storage on computer
systems today.
Background
The first hard drive of IBM’s RAMAC in 1956
Background
5MB Hard Disk in 1956
The first hard disk
was the one in the
IBM 350 RAMAC
(Random Access
Method of
Accounting and
Control) computer.
It was invented in
1956, and it stored
5 million
characters (about
5 megabytes) on
fifty 24-inch
diameter platters.
Background
A typical SCSI hard drive
Background
Read/Write Head Movement
Background
Close-up of a hard disk head
Storage Devices
Hard Disk
Storage Devices
Hard Disk
You can see from the previous diagram a hard disk
is made up of Sectors, Tracks and Cylinders.
The specification of a hard disk depends not only
on its capacity but also:
Access time to data. This is affected by the rotation
Speed of the disk and also the way in which the disk
Is connected to the motherboard – standard being
SCSI and IDE
Storage Devices
Optical disks
CD ROM = Compact Disk Read Only Memory, is an
ideal device for storing large quantities of data and
information such as large software packages.
Optical Disc Drive
Storage Devices
Optical disks
CD ROM as the name suggests is Read Only
Writable CDs allow for large amounts of data to be
written to a CD as well as read from it. They are
sometimes know as CD-RW.
For these, a CD drive is needed which includes write
heads as well as read heads
Storage Devices
Optical disks
DVD or Digital Versatile Disk is a higher capacity
version of a CD and DVD drives have a higher
transfer rate.
DVD disks provide high quality playback of films and
audio and are increasingly found as standard on the
home PC.
DVDs may be read only or read/write. They are
sometimes know as DVD-ROM and DVD-RW.
Storage Devices
Optical disks
DVD disks are double sided so data is stored on
both sides of the disk.
DVD disks typically holds 4.7 Gbytes of data
Rewritable disks can be re-used thousands of times.
Storage Devices
Blu-ray Discs
Blu-rays discs are abbreviated as
BD are used for high-definition
video storage. It is often used by
gamers. Blu-ray discs are similar
to the CD's and DVD's in their
looks. It is the memory space
which makes all the difference
between the CD's, DVD's and
BD's. Blu-ray disc is an optical
storage device.
Storage Devices
USB Flash Drive
It has an integrated Universal Serial Bus
(USB) interface. They are non-volatile
and data can be rewritten on them. They
are very small in size, but have very
large memory space.
Storage Devices
Memory Cards
They can be used in various
electronic devices from hand held
computers, mobile phones,
cameras, etc. They are also
rewritable.
Storage Devices
Exercises
1. Optical disks use which technology?
2. CDs are read only TRUE or FALSE? Explain.
3. Why is a DVD of higher capacity, compared to a CD?
4. DVDs are read only TRUE or FALSE?
5. DVD disks typically holds
6. Do you need to back up a hard disk?
7. List five backup storage devices.
1.
2.
3.
4.
5.
Storage Devices
Exercises
1. What is Primary Storage?
2. What is Secondary Storage?
3. What material is a floppy disk made from?
4. When the small window on one corner of a floppy disk is
closed, the disk is write protected TRUE or FALSE?
5. Give two advantages of floppy disks.
6. A Hard drive has cylinders, and
7. Hard drives have read/ heads.
8. The specification of a hard disk depends on:
1.
2.
3.
9. What does SCSI stand for?
