This document discusses data storage and memory. It explains that instructions and data are stored in main memory which is made up of bytes that each hold 8 bits. It defines different units of measurement for memory size like kilobytes, megabytes, and gigabytes. The document outlines different types of memory like RAM, ROM, SRAM, and DRAM. It also describes various storage devices like floppy disks, hard drives, magnetic tapes, CDs, DVDs, and backup devices like tape streamers, zip drives, and jaz drives.

1. Storing Data
Abdul Wajid
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2. Storage of Data
Instructions and data are held in main memory
which is divided into millions of addressable
storage units called bytes.
One byte can hold one character
One byte can hold 8 bits
Computers work by using pulses of voltage
which represent either 1 or 0
A low voltage mean 0 and high voltage mean 1
Total bytes in main memory referred to as the
computer’s memory size.
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3. Bits
Computers use electronic circuits to
perform the tasks they are
programmed to complete.
These circuits can be in one of two
states - ‘On’ or ‘Off’.
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4. Memory Sizes measurement
I nibble
= 4 bits
I byte
= 8 bits
I kilobytes (kb)
= 1024 bytes
1 Megabytes (Mb) = 1024kilobytes
1 gigabytes (Gb) = 1024Megabytes
1 terabytes (TB) = 1024Gigabytes
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5. Memory ( Main store)
 Memory is the name given to the group of chips inside
the processing unit
 The data held in the memory is available to the computer
Memory is used to hold following information
 Programs
 Input data
 Working Area
 Output data
 There are two types of main memory
 Ram (Random access memory )
 ROM (Read only memory )
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6. RAM & ROM
Ram
ROM
Its temporary memory Its Permanent memory
Read and Write data It can only be read
Data can be changed Data can not change or
deleted
or deleted
It is a Volatile memory It is non Volatile
The instructions are
The instructions
written into Rom at
written in Ram at the
manufacturing time.
time of execution
(BIOS)
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7. Semiconductor
Volatile
Memory
types
Non-volatile
RAM
SRAM
ROM
DRAM
PROM
EPROM
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8. PROM & EPROM
PROM
 Programmable read only
memory
 User can write instruction
only one time
 Instructions can not be
erased
 If there is error while
writing on PROM ,it
becomes unusable
EPROM
 Erasable programmable
Rom
 User can write instruction
many times
 Instructions can be
erased
 If there is error while
writing on EPROM, it can
still be used again
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9. SRAM & DRAM
SRAM
Static Random Access
Memory
It can store its value
without any need to
refresh the data as
long as the power is
available
It utilizes less power
It is more expansive
DRAM
Dynamic Random
Access Memory
It has to be refreshed
after each read
operation.
It utilizes more power
It is less expansive
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10. Floppy Disk
Used to transfer small amount of data between
computers
Come with 3.5 inch disk drive
Floppy disk is the hard case the disk inside in
floppy
Magnetic disk store binary data as a magnetic
pattern on the disk surface
It hold 1.44MB of data
Before the data is stored on a disk the disk
needs to be formatted
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11. Hard drives
 Consist a several disks on a single
spindle
 Each disk surface able to store data
 Each surface can have its own
read/write head
 This enables the read/write heads to
operate simultaneously which means
that the data can be transferred more
quickly than by using the large disk
 Hard disk is available in all sorts of
sizes
 A typical computer will have a hard disk
capacity of around 20 GB
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12. Hard Disk Mechanism
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13. Magnetic Tape
Large spools of tape are used very large
computer systems that need to hold huge
amount of data
They are not as common as they used to
be
They look similar to audio cassettes
except they are larger
Their main use is for making backup
copies of hard disk
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14. CD-ROM Drives
Use the same technology as music CD and CD
players
The data is stored on the disk digitally and a
laser beam is used to read the disk
Light is used to read the disk the data may be
packed closely and disk therefore has a huge
capacity
Are included in multimedia system
CD-ROMs can be filled with clip art
,encyclopedia ,photograph and all sort of data
Are read only disk
A CD holds around 600MB data
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15. CD-R
A CD recordable (CD-R) drive has a
read/write capability.
Using this device you can write around 15
minutes
CD-R can be used to back up hard drives.
Standard CD-R disks can be written to
only once but there is a type of disks can
be written, erased and rewritten
They are more expensive than CD-R
disks
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16. Digital Versatile Disks (DVD)
 Are similar to CD-ROMs in that they look identical and
are used to store lots of date.
 Like CD-ROM they can be used to store computer
application software, multimedia programs and full length
movies
 This is because CD-Rom typically store 650 MB of data
whereas to a DVD stores between 4.7 GB
 DVDs also are used to store movies where they produce
much better quality pictures and sound compared to a
normal video tape.
 A film stored on DVD can even be made to offer the
viewer a choice of several languages in which it can be
played back
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17. Backup devices
It is important to take regular backups of both
data and programs for security purposes.
Floppy disks do not have a very high storage
capacity and so are seldom used for backup.
Instead higher capacity and faster storage
devices are used and main ones are as follows
Tape streamers
Zip drives
Jaz drives
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18. Tape streamers
Are devices used to backup the data contained
on hard drives
Zip Drives
Are useful for backing up hard drives
They are high storage capacity floppy disks
which are slightly larger and twice as thick as
normal floppies
They can typical store data 100 MB or 250 MB
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19. Jaz Drives
Is a removable disk drive which is very
fast at transferring data.
Each disk hold up to 2 GB of data
The higher data transfer rate means that
they can be used to backup data in a very
short time
They can be used for everyday storage
just like an ordinary disk drive
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