08/12/2019 Introduction of Secondary Memory - GeeksforGeeks
Introduction of Secondary Memory
Primary memory has limited storage capacity and is volatile. Secondary memory overcome this limitation
by providing permanent storage of data and in bulk quantity. Secondary memory is also termed as
external memory and refers to the various storage media on which a computer can store data and
programs. The Secondary storage media can be fixed or removable. Fixed Storage media is an internal
storage medium like hard disk that is fixed inside the computer. Storage medium that are portable and
can be taken outside the computer are termed as removable storage media.
Difference between Primary Memory and Secondary Memory:
PRIMARY MEMORY SECONDARY MEMORY
Primary memory is directly accessed by the Secondary memory is not accessed directly by
Central Processing Unit(CPU). the Central Processing Unit(CPU). Instead, data
accessed from a secondary memory is first
loaded into Random Access Memory(RAM) and
is then sent to the Processing Unit.
RAM provides much faster accessing speed to Secondary Memory is slower in data accessing.
data than secondary memory. By loading Typically primary memory is six times faster than
software programs and required files into the secondary memory.
primary memory(RAM), computer can process
data much more quickly.
Primary memory, i.e. Random Access Secondary memory provides a feature of being
Memory(RAM) is volatile and gets completely non-volatile, which means it can hold on to its
erased when a computer is shut down. data with or without electrical power supply.
Uses of Secondary Media:
Permanent Storage: Primary Memory (RAM) is volatile, i.e. it loses all information when the
electricity is turned off, so in order to secure the data permanently in the device, Secondary storage
devices are needed.
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Portability: Storage medium, like the CDs, flash drives can be used to transfer the data from one
devive to another.
Fixed and Removable Storage
Fixed Storage-
A Fixed storage is an internal media device that is used by a computer system to store data, and usually
these are referred to as the Fixed Disks drives or the Hard Drives.
Fixed storage devices are literally not fixed, obviously these can be removed from the system for
repairing work, maintenance purpose, and also for upgrade etc. But in general, this can’t be done
without a proper toolkit to open up the computer system to provide physical access, and that needs to be
done by an engineer.
Technically, almost all of the data i.e. being processed on a computer system is stored on some type of a
built-in fixed storage device.
Types of fixed storage:
Internal flash memory (rare)
SSD (solid-state disk) units
Hard disk drives (HDD)
Removable Storage-
A Removable storage is an external media device that is used by a computer system to store data, and
usually these are referred to as the Removable Disks drives or the External Drives.
Removable storage is any type of storage device that can be removed/ejected from a computer system
while the system is running. Examples of external devices include CDs, DVDs and Blu-Ray disk drives,
as well as diskettes and USB drives. Removable storage makes it easier for a user to transfer data from
one computer system to another.
In a storage factors, the main benefit of removable disks is that they can provide the fast data transfer
rates associated with storage area networks (SANs)
Types of Removable Storage:
Optical discs (CDs, DVDs, Blu-ray discs)
Memory cards
Floppy disks
Magnetic tapes
Disk packs
Paper storage (punched tapes , punched cards)
Secondary Storage Media
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There are the following main types of storage media:
1. Magnetic storage media:
Magnetic media is coated with a magnetic layer which is magnetized in clockwise or anticlockwise
directions. When the disk moves, the head interprets the data stored at a specific location in binary 1s
and 0s at reading.
Examples: hard disks, floppy disks and magnetic tapes.
Floppy Disk: A floppy disk is a flexible disk with a magnetic coating on it. It is packaged inside a
protective plastic envelope. These are one of the oldest type of portable storage devices that could
store up to 1.44 MB of data but now they are not used due to very less memory storage.
Hard disk: A hard disk consists of one or more circular disks called platters which are mounted on
a common spindle. Each surface of a platter is coated with a magnetic material. Both surfaces of
each disk are capable of storing data except the top and bottom disk where only the inner surface
is used. The information is recorded on the surface of the rotating disk by magnetic read/write
heads. These heads are joined to a common arm known as access arm.
Hard disk drive components:
Most of the basic types of hard drives contains a number of disk platters that are placed around a
spindle which is placed inside a sealed chamber. The chamber also includes read/write head and
motors. Data is stored on each of these disks in the arrangement of concentric circles called tracks
which are divided further into sectors. Though internal Hard drives are not very portable and used
internally in a computer system, external hard disks can be used as a substitute for portable
storage. Hard disks can store data upto several terabytes.
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2. Optical storage media
In optical storage media information is stored and read using a laser beam. The data is stored as a spiral
pattern of pits and ridges denoting binary 0 and binary 1.
Examples: CDs and DVDs
Compact Disk: A Compact Disc drive(CDD) is a device that a computer uses to read data that is
encoded digitally on a compact disc(CD). A CD drive can be installed inside a computer’s
compartment, provided with an opening for easier disc tray access or it can be used by a peripheral
device connected to one of the ports provided in the computer system.A compact disk or CD can
store approximately 650 to 700 megabytes of data. A computer should possess a CD Drive to read
the CDs. There are three types of CDs:
CD- ROM CD-R CD-RW
It stands for Compact Disk – It stands for Compact Disk- It stands for Compact Disk-
Read Only Memory Recordable. Rewritable.
Data is written on these disks Data can be recorded on these It can be read or written
at the time of manufacture. disks but only once. Once the multiple times but a CD-RW
This data cannot be changed, data is written in a CD-R, it drive needs to be installed on
once is it written by the cannot be erased/modified. your computer before editing a
manufacturer, but can only be CD-RW.
read. CD- ROMs are used for
text, audio and video
distribution like games,
encyclopedias and application
software.
DVD:
It stands for Digital Versatile Disk or Digital Video Disk. It looks just like a CD and use a similar
technology as that of the CDs but allows tracks to be spaced closely enough to store data that is
more than six times the CD’s capacity. It is a significant advancement in portable storage
technology. A DVD holds 4.7 GB to 17 GB of data.
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Blue Ray Disk:
This is the latest optical storage media to store high definition audio and video. It is similar to a CD
or DVD but can store up to 27 GB of data on a single layer disk and up to 54 GB of data on a dual
layer disk. While CDs or DVDs use red laser beam, the blue ray disk uses a blue laser to read/write
data on a disk.
3. Solid State Memories
Solid-state storage devices are based on electronic circuits with no moving parts like the reels of tape,
spinning discs etc. Solid-state storage devices use special memories called flash memory to store data.
Solid state drive (or flash memory) is used mainly in digital cameras, pen drives or USB flash drives.
Pen Drives:
Pen Drives or Thumb drives or Flash drives are the recently emerged portable storage media. It is an
EEPROM based flash memory which can be repeatedly erased and written using electric signals. This
memory is accompanied with a USB connector which enables the pendrive to connect to the computer.
They have a capacity smaller than a hard disk but greater than a CD. Pendrive has following
advantages:
Transfer Files:
A pen drive being plugged into a USB port of the system can be used as a device to transfer files,
documents and photos to a PC and also vice versa. Similarly, selected files can be transferred
between a pen drive and any type of workstation.
Portability:
The lightweight nature and smaller size of a pen drive make it possible to carry it from place to
place which makes data transportation an easier task.
Backup Storage:
Most of the pen drives now come with a feature of having password encryption, important
information related to family, medical records and photos can be stored on them as a backup.
Transport Data:
Professionals/Students can now easily transport large data files and video/audio lectures on a pen
drive and gain access to them from anywhere. Independent PC technicians can store work-related
utility tools, various programs and files on a high-speed 64 GB pen drive and move from one site to
another.
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