INTRODUCTION TO

COMPUTING

Memory / Storage
 Objectives
• Name some general properties of storage systems
• Describe common types of hard drives and their uses
• Discuss various types of optical discs available and how they differ
from each other

• Identify some flash-memory-based storage devices and media and

explain how they are used today.

• Use appropriate storage systems based on its need.

 Outline
Primary Storage

Storage Characteristics

Secondary Storage

Other Types of Memory / Storage

 Memory / Storage

Memory

▪ It refers to chip-based storage

located inside the System Unit.

▪ The electronic that holds place for

instructions and data which the
microprocessors can reach quickly .
 Memory / Storage
• Read Only Memory (ROM)
▪ Allows only readout capability
▪ Non Volatile chips located on the motherboard into
which data or programs have been permanently
stored.

▪ Being replaced with flash memory

 Memory / Storage
• Programmable Read Only Memory (PROM)
▪ Enables the user to add special information to the ROM
▪ A blank ROM chip that can be written to permanently.
• EEPROM (Electrically erasable programmable
read-only memory)
▪ Allows a programmer to erase the microcode with an
electrical signal

• Virtual Memory
▪ An imaginary memory area supported by the software in
conjunction with the hardware
 Primary Storage

• Random Access Memory (RAM)

▪ Computer’s main memory (Primary Storage)
▪ Volatile
▪ Allows instructions and data to be stored, changed
and retrieved by the user

• Most personal computers used SD-RAM

• MRAM and PRAM - non volatile under development

 Primary Storage
Random Access Memory (RAM)

Dynamic RAM Static RAM Magneto resistive

• Chips must be • Chips are faster and RAM
re-energized more reliable than any • Stores data using
constantly or they lose variation of DRAM magnetic charges
their contents. • These chips do not instead of electrical
have to be charges.
re-energized as • MRAM has greater
DRAM. storage capacity,
• More expensive consumes less power,
and has faster access
times.
 Primary Storage

• Registers
▪ High-speed memory built into the CPU
▪ Used to store data and intermediary results during
processing

▪ Fastest type of memory

 Primary Storage
• Cache
▪ Memory cache helps speeds the processes of the
computer because it stores frequently used
instructions and data.
 Primary Storage
• CMOS
▪ Complimentary Metal-Oxide Semiconductor
▪ Some memory chips use CMOS technology because it
provides high speeds and consumes little power.

▪ CMOS technology uses battery power to retain information

even when the power to the computer is off.
 Secondary Storage

• Memory Subsystem
▪ also known as the “secondary storage”
▪ allows for extra data storage, exceeding the CPU’s
primary storage

▪ an efficient and compact means of sorting large amount of

data, ready for retrieval or further processing
Secondary Storage
 Secondary Storage
• Secondary Storage
▪ Floppy Disks
▪ Compact Disc
▪ Digital Versatile Disc
▪ Zip Disk
▪ Hard Disk
▪ Tape
Storage System Characteristics
• Can be internal, external, or remote
• Are nonvolatile
• Usually use random access; can be sequential
• Memory size refers to the number of bytes the device has
available for storage. It is measured in kilobytes (KB),
megabytes (MB), gigabytes (GB), or terabytes (TB)

• Types of storage Technology Used

▪ Magnetic (Conventional hard drives)
▪ Optical (Optical discs)
▪ Electrons (flash memory media)
Logical vs Physical Representation

•Logical file representation

Individuals view a document stored as one complete
unit in a particular folder on a particular drive

•Physical file representation

Computers access a particular document stored on a
storage medium using its physical location/s
 Logical vs Physical Representation
▪ File - Anything stored on storage medium, such as program,
document, digital image, or song

▪ Filename - Name given to a file by the user

▪ Folder - Named place on a storage medium into which files can

be stored
 Hard Drives

• Hard Drives
A hard disk contains one or more
inflexible, circular platters that use
magnetic particles to store data,
instructions, and information
 Hard Drives

• Hard Disks are divided into

▪ Tracks - Concentric path on disk where data is
recorded

▪ Sectors - A small piece of the track

▪ Clusters - One or more sectors; smallest

addressable area of a disk

▪ Cylinders - Collection of tracks located in the

same location on a set of hard disk surfaces
 Hard Drives
•Magnetic Hard Drives
One or more permanently sealed metal magnetic disks
with an access mechanism and read / write heads
 Hard Drives
• Solid State Drives (SDDs)
▪ Use flash memory technology
▪ Use less power and have no moving parts
▪ Particularly appropriate for portable computers and mobile devices
External Hard Drives

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 Hard Drive Speed and Caching
• Disk access time:
▪ Total time that it takes for a hard drive to read or write data
▪ Consists of seek time, rotational delay, and data movement time
• Disk cache
▪ Dedicated part of RAM used to store additional data adjacent to data
retrieved during a disk fetch to improve system performance
• Hybrid hard drive
▪ Combination of flash memory and magnetic hard drive
▪ Uses flash memory for cache
▪ Allows encryption to be built into the drive

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Hybrid Hard Drives

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 Optical Discs
• Optical discs: store data optically (using laser beams)
▪ Divided into sectors like magnetic discs but use a single spiral track
(groove)

▪ Data is stored in 0s and 1s

• Pits and lands are used to represent 1s and 0s, the transition between a pit
and a land represents a 1; no transition represents a 0

• Can be:
• Read-only: Surface is molded or stamped to represent the data
• Recordable or rewritable: Reflectivity of surface is changed by a laser

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Optical Discs

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 Optical Discs
• Read-only disc: Can be read from, but not written to, by the
user
• Recordable disc: Can be written to, but cannot be erased and
reused
• Rewritable disc: Can be recorded on, erased, and overwritten

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 Optical
• Optical drives: Designed Drives
for type of disc: CD, DVD, or Blu-Ray Disc
(BD)
▪ Can be read-only, recordable, or rewritable
▪ Downward compatible
▪ Can support single or dual layer discs
• Burning: Recording data onto disc
▪ CD discs: Use infrared lasers; hold 650 MB
▪ DVD discs: Use red lasers; hold 4.7 GB (single-layer)
▪ BD discs: Use blue-violet lasers; hold 25 GB (single-layer)
• Can be internal or external drives
• External drives typically USB 29
 Flash Memory

• Non-volatile memory chips that can be used for storage

• Now stores firmware for personal and other devices

• Built into many types of devices

• Most often found in the form of:

▪ Flash memory cards
▪ USB flash drives
▪ Solid-state drives
▪ Hybrid hard drives
Flash Memory

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 Flash Memory

▪ Memory Card
A removable flash memory device
that can be inserted and removed from
a slot in computer, mobile device, or
card reader/ writer

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 Flash Memory
• USB Flash Drive
▪ Consist of flash memory media and a reader in a
single self-contained unit

▪ Typically portable drives that connect to and are

powered by a USB port

▪ Also called USB flash memory drives, thumb

drives, jump drives

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 Other Types of Memory / Storage
• Tape
▪ Tape is a magnetic called coated ribbon of plastic capable of
storing large amounts of data and information

▪ A Tape drive reads and writes data and information on a tape

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 Other Types of Memory / Storage
• Magnetic Stripe Cards
▪ A credit card, entertainment card, bank card, or other similar
card with a stripe that contains information identifying the card
and its owner

▪ A magnetic stripe reader read information stored on the stripe

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 Other Types of Memory / Storage

• Smart Card
▪ Similar in size to a credit card or ATM
card which stores data on a thin
microprocessor embedded in the card

▪ When inserted in a specialized card

reader, the information on the smart card
is read and if necessary, updated

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 Other Types of Memory / Storage

• Microfilm & Microfiche

▪ Store images of documents on roll or
sheet film

▪ Microfiche is a small sheet of film,

usually about 4” x 6”

▪ Microfilm is a 100 to 215 ft. roll of film

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 Other Types of Memory / Storage
• Microfilm & Microfiche
▪ A computer output microfilm recorder is the device that
records the image on the film

▪ The stored images are so small that you can read them only with a
microfilm or microfiche reader

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Other Types of Memory / Storage

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 Other Types of Memory / Storage

• Storage server
▪ Hardware device containing
multiple high-speed hard drives

▪ Usually scalable so additional

hard drives can be added as
needed

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 Other Types of Memory / Storage

• Enterprise Storage
▪ Stores huge volumes of data and
information for large businesses

▪ Uses special hardware for heavy use,

maximum availability, and maximum
efficiency

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 Other Types of Memory / Storage

• RAID (redundant arrays of independent discs)

Method of storing data on two or more hard drives that work together to
do the job of a larger drive

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 Other Types of Memory / Storage
• Holographic storage
▪ Store data as holograms
▪ Emerging type of 3D storage technology

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Other Types of Memory / Storage
• Remote storage
Using a storage device not directly a part of the computer being used
▪ Network Attached Storage (NAS)
Connected directly to a network
▪ Storage Area Network (SAN)
Separate network of hard drives or other storage devices which is
attached to the main network
▪ Online Storage or Cloud Storage
A service on the web which provides storage to computer users,
usually for minimal monthly fee

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Other Types of Memory / Storage

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