STORAGE DEVICES
Towards the end of this unit you will be
able to identify the type of storage
devices and their storage capacity
WHAT IS STORING ?
STORAGE CAPACITY
• Storage capacities and file sizes are measured
from lowest to highest in:
• bits
• bytes
• kilobytes
• megabytes
• gigabytes
• Terabytes
Relationship between measurement
8 bits
1024 bytes
1024 kilobytes
1024 megabytes
1024 gigabytes
1000
Terabyte
1000
Terabyte
1 byte
1 kilobyte
1 megabyte
1 gigabyte
1 terabyte
11Petabyte
Petabyte
ACTIVITY
•
•
•
•
•
•
PLACE THE FOLLOWING MEASURING UNIT IN TERMS
OF THEIR STORAGE CAPACITY FROM SMALLEST TO
LARGEST
bits
Kilobytes
Gigabytes
Terabytes
Megabytes
Bytes
STORAGE DEVICES USED IN A
COMPUTER
• A computer uses two types of storage.
• A main store consisting of ROM and RAM,
and
• backing stores which can be internal, eg hard
disk, or external, eg a CD or USB flash drive.
HOME WORK
• DRAW THE MEASUREMENT RELATIONSHIP
TABLE
• 8 bits……….. 1 byte.
• ………………………….
• ………………………….
• ………………………….
• ………………….. 1 terabyte
MAIN STORE (COMPUTER MEMORY)
• Main store (or computer memory) is divided into
Read Only Memory (ROM) and Random Access
Memory (RAM).
• ROM (NON VOLATILE MEMORY)
• ROM is memory that cannot be changed by a
program or user. ROM retains its memory even
after the computer is turned off. For example,
ROM stores the instructions for the computer to
start up when it is turned on again.
RAM
RAM (VOLATILE MEMORY)
• In the case of RAM, it is volatile (this means
that when power is switched off all of the data
in the memory disappears). Main memory is
used to store data whilst it is being processed
by the CPU. Data can be put into memory, and
read back from it, very quickly.
ROM AND RAM
INTERNAL BACKING STORE-HARD DISK
• The main internal backing store is a computer's hard
disk.
• A hard disk stores:
 the operating system
 software applications or programs
 the majority of your data files
Note: Hard disks store large amounts of data - 200GB to
1TB is common in desktop computers. The data stored
on a hard disk is retained until deleted, but it needs to
be loaded into main store RAM before it can be used.
HARD DISK
ACTIVITY
1.Which of the following retains its data even after the computer is switched
off?
ROM
RAM
REM
2. What does RAM stand for?
random accessible memory
random access memory
random allowable memory
3. What is a computer's main internal backing store?
CD-ROM
ROM
hard disk
4. How best is the size of a hard disk measured?
kilobytes
megabytes
gigabytes
ANSWERS
1.Which of the following retains its data even after the computer is switched off?
ROM
RAM
REM
2. What does RAM stand for?
random accessible memory
random access memory
random allowable memory
3. What is a computer's main internal backing store?
CD-ROM
ROM
hard disk
4. How best is the size of a hard disk measured?
kilobytes
megabytes
gigabytes
MAGNETIC STORAGE MEDIUM-Floppy disks
oFloppy disks hold very small amounts of
data, just 1.44MB and a computer needs a
floppy drive to read them.
oThey are used to:
transfer small files of data from
one machine to another
backup important small files that are
stored on your hard disk
store restricted files that you don't
want other users of your computer seeing
MAGNETIC STORAGE MEDIUM-ZIP DISK
• Zip disks are like large floppy disks but can
store 250MB or more of data. To read them a
computer needs a zip drive. Their use is
similar to that of floppy disks.
MAGNETIC STORAGE MEDIUM- HARD
DRIVES
• Hard Drives- There are two types of Hard Drives.
One is Internal that we studied earlier. The other
is an Portable Hard Drive.
• A portable hard-drive is one that is placed into a
small case along with some electronics that allow
the hard-drive to be accessed using a USB or
similar connection.
Portable hard-drives allow very large amounts of
data to be transported from computer to
computer.
• HARD DRIVES ARE RANDOM ACCESS DEVICES
MAGNETIC STORAGE DEVICESMAGNETIC TAPE
• MAGNETIC TAPE:
• Magnetic tape are serial access devices and
are used only where batch processing is used.
• Advantages: (i) Tape is light and compact
and easy to carry and yet it stores far more
data than floppy discs.