This document discusses different types of computer memory and storage devices. It describes volatile memory like RAM that loses data when power is removed, and non-volatile memory like ROM that retains data without power. RAM is divided into SRAM and DRAM. Storage devices include hard disks with platters that store data magnetically, floppy disks, CDs, DVDs, and magnetic tapes. Each storage type has advantages for different use cases in terms of capacity, portability, write capabilities, and more.

1. External memories; volatile, non-
volatile, RAM, Hard Disk and Optical
Drives

2. Index
• Introduction
• Memory
– Volatile
• RAM
– SRAM
– DRAM
– Non volatile
• Differnce between RAM and ROM
• Storage devices
– Hard disk
– Floppy disk
– Magnetic Disk
– Optical
• CD-ROM
• CD-Recordable (CD-R)
• CD-R/W
• DVD
– Magnetic Tape

3. INTRODUCTION
• Computer memory is the storage space in
computer where data is to be processed and
instructions required for processing are
stored.
• Memory is primarily of two types
• Internal Memory - cache memory and
primary/main memory
• External Memory - magnetic disk / optical
disk etc.

4. Memory Classificatioin

5. Volatile memory:
• It also known as volatile storage & temporary
memory.
• Volatile memory retains the information as
long as power supply is on, but when power
supply is off or interrupted the stored memory
is lost.
• Eg : RAM

6. Non-volatile Memory:
• Non-volatile memory is typically used for the
task of secondary storage, or long-term
persistent storage
• Examples of non-volatile memory
include read-only memory flash memory and
early computer storage methods such
as paper tape and punched cards.

7. RAM
• A RAM constitutes the internal memory of the
CPU for storing data, program and program
result
• It is read/write memory. It is called random
access memory (RAM).
• RAM is of two types:
– Static RAM (SRAM)
– Dynamic RAM (DRAM)

8. STATIC RAM (SRAM)
• The word static indicates that the memory
retains its contents as long as power remains
applied.
• SRAM chips use a matrix of 6-transistors and no
capacitors.
• Static RAM is used as cache memory needs to be
very fast and small.
• SRAM uses more chips than DRAM for the same
amount of storage space, thus making the
manufacturing costs higher.

9. DYNAMIC RAM (DRAM)
• DRAM, unlike SRAM, must be
continually refreshed in order for it to
maintain the data.
• All DRAMs are made up of memory cells.
These cells are composed of one capacitor and
one transistor.
• DRAM is used for most system memory
because it is cheap and small

10. Difference between RAM & ROM
RAM ROM
VOLATILE MEMORY NON VOLATILE
Data in ram is not permanently written
when power off, data deleted
Permanently, not erased
Ram: DRAM & SRAM ROM: PROM & EPROM
It requires flow of electricity to retain data It does not requires electricity to retain
data
Ram is the memory available for the
operating system programs and process
to use when the computer is running
Rom is the memory that comes with your
computer that is pre-written to hold the
instructions for booting up the computer

11. STORAGE DEVICES :
• Storage devices are used to maintain
programs, data, and information for later use.
• Storage devices include: magnetic tapes,
magnetic disks, floppy disks, zip disks, optical
discs, CDs, DVDs, and hard disks
• Primary storage: is the storage provided by
memory in a computer system .

12. Hard Disks
• 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.
• The basic technology used in hard disks is similar to that of magnetic tape
• Magnetic material is layered onto a high-precision aluminum disk
• The disk head can move to any point on the platter almost instantly
compared to tape
• With tape, the head touches the tape. With disks, the head never
touches the platter
• Tape moves at approx 5 cm/s. Disk platters move at up to 7500 cm/s (272
km/h!)

13. Floppy Disk:
• A floppy disk is a low capacity disk which may be removed from the
computer.
• Those holding a small amount of data (typically 1.44 Mb) and ‘Super
floppies’ known as ZIP disks (typically 100 Mb)
• Data may be written to and read from a floppy. A small notch can be
used to make the disk read-only.
• 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

14. Magnetic Disks :
• Disk substrate coated with
magnetizable material (iron
oxide…rust)
• Substrate originally was aluminium - Is
now glass
– Improved surface uniformity
• Increases reliability
– Reduction in surface defects
• Reduced read/write errors
– Lower flight heights (head rides on air gap)
– Better stiffness
– Better shock/damage resistance

15. Disk Data Layout
•The platter in a concentric set of
ringds called Tracks
•There can be thousands of tracks
per surface
•Adjacent tracks are separated by
gaps
•Data are transferred to and from
the disk in sectors

16. Cylinders
•The set of all tracks in the
same relative position on the
platter is referred to as a
cylinder
•All shaded part are cylinder

17. Multiple Platters
• Multiple –platter disks
employ a movable head, with
one read write per platter
• All heads are mechanically
fixed so that all are at the same
distance from the centre of the
disk and move together

18. Optical Storage devices
The most widely used type of optical storage medium are as follows

19. • Originally for audio
• 650Mbytes giving over 70 minutes audio
• Polycarbonate coated with highly reflective
coat, usually aluminium
• Data stored as pits
• Read by reflecting laser
• Constant packing density
• Constant linear velocity
Optical Storage CD-ROM

20. CD-ROM Format
• Mode 0=blank data field
• Mode 1=2048 byte data+error correction
• Mode 2=2336 byte data

21. CD-ROM for & against
• Large capacity (?)
• Easy to mass produce
• Removable
• Robust
• Expensive for small runs
• Slow
• Read only

22. Other Optical Storage
• CD-Recordable (CD-R)
– WORM
– Now affordable
– Compatible with CD-ROM drives
• CD-RW
– Erasable
– Getting cheaper
– Mostly CD-ROM drive compatible
– Phase change
• Material has two different reflectivity's in different phase
states

23. DVD - what’s in a name?
• Digital Video Disk
– Used to indicate a player for movies
• Only plays video disks
• Digital Versatile Disk
– Used to indicate a computer drive
• Will read computer disks and play video disks
• Dogs Veritable Dinner
• Officially - nothing!!!

24. DVD - technology
• Multi-layer
• Very high capacity (4.7G per layer)
• Full length movie on single disk
– Using MPEG compression
• Finally standardized (honest!)
• Movies carry regional coding
• Players only play correct region films
• Can be “fixed”

25. DVD – Writable
• Loads of trouble with standards
• First generation DVD drives may not read first
generation DVD-W disks
• First generation DVD drives may not read CD-
RW disks
• Wait for it to settle down before buying!

27. Magnetic Tape

28. Conclusion
• If there is one thing that nearly every computer
owner needs, it is a place to store his data. Data
storage is one of the areas of computing that has
evolved most in recent years, and computer
storage devices are now incredibly varied in
terms of cost, performance, size and storage
space. Each type of computer storage device has
its own advantages, and you may find that the
ideal solution for your storage needs involves a
combination of storage types.

29. REFERENCES:
http://en.wikipedia.org/wiki/Volatile_
memory
http://en.wikipedia.org/wiki/Non-
volatile_memory
http://en.wikipedia.org/wiki/Compute
r_data_storage