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M. GuymonPleasant Grove High School
Spring 2003
Storage Devices

What is Storage Devices??
 A storage device is any device used in
a computer to store information
 A storage device will retain this
information when the computer is
switched off.
M. Guymon
Pleasant Grove High School
Spring 2003

Hardwares of
3
What are Types of Storage
Devices?
Storage DevicesStorage Devices
Primary StoragePrimary Storage Secondary StorageSecondary Storage
Read-Only MemoryRead-Only Memory
(ROM)(ROM)
Random-Access MemoryRandom-Access Memory
(RAM)(RAM)
Figure 9. Classification of storage devices.

Hardwares of
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What is Primary Storage?
 Primary storage is computer memory
that is directly accessible to the CPU
of a computer without the use of
computer's input/output channels.
 Primary storage is used to store data
that is likely to be in active use.

M. Guymon
Spring 2003
Static Memory vs Dynamic Memory
 This approach assumes that
addresses don’t change
 The static memory allocation
may be through absolute
addressing or dynamic
addressing but in either case
,the compiler or assembler
generates a set of addresses
that does not change for the
life of the program
 This approach assumes that
addresses may change
The two approach used are
stack frames and pointer
handlers
 Stack frames are used for
temporary storage and Pointer
handlers are used for dynamic
allocation

Memory
types
RAM ROM
SRAM DRAM PROM EPROM
Volatile Non-volatile
Semiconductor

Hardwares of
7
What is ROM?
 Read-only memory
(ROM) is a class of
storage media used in
computers.
 Data stored in ROM
cannot be modified.
 ROM is a non-volatile
storage. Data remains
unchanged even after
switching off the
computer. (Wikipedia,
2007n)
 E.g. EPROM, EEPROM
Figure 10. An EPROM.
(Wikipedia, 2007n)

ROM ‘Discussion’ (2)
Most personal computers contain a small
amount of ROM that stores critical programs such
as the program that boots the computer. In
addition, ROMs are used extensively in calculators
and peripheral devices such as laser printers,
whose fonts are often stored in ROMs.
A variation of a ROM is a PROM
(programmable read-only memory). PROMs are
manufactured as blank chips on which data can
be written with a special device called a PROM
programmer .

Hardwares of
9
What is RAM?
 Random access memory
(RAM) is a type of data
storage used in
computers.
 It takes the form of
integrated circuits that
allow the stored data to
be accessed in any order
(random).
 Data stored in RAM can
be modified.
 RAM is a volatile storage.
Data will lose after
switching off the
computer. (Wikipedia,
2007o)
 E.g. DDRam, DDR-2
Ram
Figure 11. Two 512 MB DDRam.

Two types: Dynamic RAM and Static RAM. The
two types differ in the technology they use to hold
data, dynamic RAM being the more common type.
Dynamic RAM needs to be refreshed thousands of
times per second.
Static RAM does not need to be refreshed,
which makes it faster; but it is also more expensive
than dynamic RAM. Both types of RAM are volatile,
meaning that they lose their contents when the
power is turned off.

M. Guymon
Spring 2003
RAM vs. ROM
 RAM
 “Random Access
Memory”
 The ability of a storage
device to go directly to a
specific storage location
without having to search
sequentially from a
beginning location.
 Very volatile
• Cannot hold data when
the power is off.
• Looses all data when
power is lost.
 ROM
 “Read only memory”
 Drives can read data
from disks, but cannot
store new data on them.
 One or more integrated
circuits that contain
permanent instructions
that the computer uses
during the boot process.

Cache Memory
 Cache memory
High speed memory that a processor
can access more rapidly than main
memory
Schematic

CPU
Memory
(main store)
Cache
controller
Cache
memory
Typically
4MB
Typically
64 KB
HitMiss

Cache ‘Discussion’ (1)
Pronounced “cash”, a special high-speed storage
mechanism. It can be either a reserved section of main
memory or an independent high-speed storage device. Two
types of caching are commonly used in personal
computers: memory caching and disk caching.
A memory cache, sometimes called a cache store or
RAM cache, is a portion of memory made of high-speed
static RAM (SRAM) instead of the slower and cheaper
dynamic RAM (DRAM) used for main memory. Memory
caching is effective because most programs access the
same data or instructions over and over. By keeping as
much of this information as possible in SRAM, the computer
avoids accessing the slower DRAM.

Cache ‘Discussion’ (2)
Some memory caches are built into the architecture of
microprocessors. The Intel 80486 microprocessor, for
example, contains an 8K memory cache, and the Pentium
has a 16K cache. Such internal caches are often called
Level 1 (L1) caches. Most modern PCs also come with
external cache memory, called Level 2 (L2) caches. These
caches sit between the CPU and the DRAM. Like L1
caches, L2 caches are composed of SRAM but they are
much larger.

Cache (3)
Disk caching works under the same principle as memory
caching, but instead of using high-speed SRAM, a disk
cache uses conventional main memory. The most recently
accessed data from the disk (as well as adjacent sectors) is
stored in a memory buffer. When a program needs to
access data from the disk, it first checks the disk cache to
see if the data is there. Disk caching can dramatically
improve the performance of applications, because
accessing a byte of data in RAM can be thousands of times
faster than accessing a byte on a hard disk.

Devices for Secondary
Storage
 Magnetic tape and disks
 Compact Disk Read-Only Memory (CD-ROM)
 Write Once Read Many - (WORM)
 Magneto-optical disks
 Redundant Array of Inexpensive Disks (RAID)
 Optical disks
 Digital Video Disks
 Memory cards
 Flash memory
 Removable storage

Hardwares of Personal Comput ers 18
Secondary Storage
USB flash drives
 They are flash memory
data storage devices
integrated with a USB
interface.
 They are typically small,
lightweight, removable
and rewritable.
(Wikipedia, 2007u)
 Data capacity:
512MB, 1GB, 2GB, 4GB,
etc
Figure 18. An USB flash drive.

Secondary Storage
Memory Cards
 e.g. SD card, CF
card, xD card,
Microdrive, Memory
Stick
 Data can be read or
write
 Data capacity:
512 MB, 1GB, 2GB,
4GB etc Figure 19. A SD card.

Secondary Storage
Hard Disk
 Data can be read or
write
 Speed of disk rotation
usually 7200 rpm
 Data capacity :
80GB, 160GB,
250GB, 300GB etc
(Wikipedia, 2007r)
Figure 13. A Hard disk.

Internal Hard Disk
 Located inside system
unit
 Known as a fixed disk
 Designated as the C
drive
 Advantages over floppies
Access speed
Capacity21

Hard Disk Drive Components
 Disk platter
 Read/Write head
 Head arm/Head slider
 Head actuator mechanism
 Spindle motor
 Logic board
 Air filter
 Cables & Connectors

 The data’s are stored in this media
 Form factor
 5.5” - actual size is 5.12”
 3.5” - actual size is 3.74”
 2.5”
 1 1/8”
 1 1/3”
 1”

• The 5.25” platter were used in earlier days
• Now a days it is replaced by the 3.5” platter
•The 2.5”,1 1/8”, 1 1/3” & 1” platters are using in
the laptop computers
•Among this the 1” platter are known as
“Microdrive”

Hard disk
 The surface of a hard
disk is divided up into
Sectors and Tracks.
 Data is stored in the
‘blocks’ created by the
Sectors and Tracks.
 Moving data into a
‘block’ is called Random
Access.

M. Guymon
Spring 2003
Magnetic Storage
 Recording of data
onto disks or tape
by magnetizing
particles of an
oxide based
surface coating.
 A fairly permanent
type of storage that
can be modified.

Floppy disk
 The most common form of external
storage device used in a personal
computer is a 3.5” FLOPPY DISK.
 A high density floppy disk can hold up
to 1.4 megabytes of data.

M. Guymon
Spring 2003
Floppy Disk
 Round piece of flexible
Mylar plastic covered
with a thin layer of
magnetic oxide and
sealed inside a
protective covering.
 May be referred to as a
“floppy”
 3½ disk capacity is
1.44 MB or 1,440,000
bytes

M. Guymon
Spring 2003
Floppy Disk Options
 Formatted
Preparing the disk for use by the
computer.
 Write-protected
Setting the disk so that it can not be
written to by the computer.

M. Guymon
Spring 2003
Zip Disk
 Floppy disk technology manufactured by
Iomega.
 Available in 100 MB and 250 MB versions

M. Guymon
Spring 2003
Digital Audio Tape
 Method of storing large amounts of
data on tape using helical scan
technology to write data at high
densities across the tape at an angle.

M. Guymon
Spring 2003
Optical Storage
 Means of recording data as light and
dark spots on CD or DVD.
 Reading is done through a low-power
laser light.
Pits
• Dark spots
Lands
• Lighter, non-spotted surface areas

M. Guymon
Spring 2003
CD-ROM
 “CD – Read Only Memory”
 Also called CD-R
 CD-Read
 Storage device that uses
laser technology to read
data that is permanently
stored on compact disks,
cannot be used to write data
to a disk.

 density: 16,000 tpi
 up to 650 MBytes
 Non-erasable, non-
writeable storage
 discs are mastered,
pressed (mass
production)
 Multi-speeds drives
common
CD-ROM
39

M. Guymon
Spring 2003
CD-RW
 “CD-Read Write”
 A storage device that reads data from CD’s and also
can write data to CD’s.
 Similar to a CD-ROM, but has the ability to write to
CD.

 discs are “burnt” one at a
time
 high intensity laser beam
used for recording
pregrooved tracks
 low intensity beam for
reading
 attributes similar to CD-
ROM
CD–R
41

CD-RW
 CD-ReWritable--
writable, erasable disc
 optical phase-change
recording
 Erased, written up to
1,000 times
 UDF (Universal Disk
Format)
 variable-length packets
 fixed-length packets
42

Secondary Storage
CD-Rom CD-R CD-RW
Data can
be
Read only Read but
write once
Read &
write
Data
capacity
(MB)
650 650 650

Secondary Storage
Figure 14. A C-R disk.
Figure 15. A CD-RW disk.

Hardwares of
45
Secondary Storage
Figure 16. A DVD-R disk.
Figure 17. A DVD+RW disk.

M. Guymon
Spring 2003
DVD-ROM
 “Digital Video Disks
– Read Only
Memory”
 Reads data from
CD’s (audio and
data) and DVD’s
(data or movie)
 Cannot be used to
write data to a disk.

DVD
 Digital Versatile Disc
 second generation CD-
ROM
 higher capacity:
 higher data density
 multiple sides
 multiple layers
47ER. Avinash Bhagat ,
Senior Lecturer

Secondary Storage
DVD DVD-R
/DVD+R
DVD-RW
/DVD+RW
Data can
be
Read only Read but
write once
Read &
write
Data
capacity
(GB)
Single layer:
4.7
Double layer:
8.5
Single layer:
4.7
Double layer:
8.5
Single layer:
4.7
Double layer:
8.5

Thanks!
Hardwares of Personal Comput ers

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