A USB drive is a data storage device that
includes flash memory with an integrated
Universal Serial Bus (USB) interface
USB flash drives use the USB mass storage
standard, supported natively by modern
operating systems such as linux, Mac OS X,
Windows, and other Unix-like systems, as well
as many BIOS boot ROMs
USB drives with USB 2.0 support can store more data and
transfer faster than much larger optical disc drives like
CD-RW or DVD-RW drives.
They are smaller, faster, have thousands of times more
capacity, and are more durable and reliable because they
have no moving parts
The term drive persists because computers read and
write flash drive data using the same system commands
as for a mechanical disk drive.
A Kingston card reader which accepts
Micro SD memory cards (Transcend card
shown inserted) and acts as a USB flash
drive, resulting in a size of approximately
2 cm in length, 1 cm in width and 2 mm in
Punched cards in storage at a U.S. Federal
records center in 1959. All the data visible
here would fit on a 4 GB flash drive
STRUCTURE OF PEN DRIVE
A flash drive consists of a
Printed circuit board
Type-A USB connection
Drives for other interfaces.
Flash memory combines a number of older technologies
The memory storage was based on earlier EPROM and
Hardware designers later developed EEPROMs with the
erasure region broken up into smaller "fields" that could be
erased individually without affecting the others.
The development of high-speed serial data interfaces such as
USB and the simultaneous development of small, high-speed,
low-power microprocessor systems allowed this to be
incorporated into extremely compact systems.
Design and implementation
Internals of a typical USB
• 1 USB Standard-A plug
• 2 USB mass storage
• 3 Test points
• 4 Flash memory chip
• 5 Crystal oscillator
• 6 LED
• 7 Write-protect switch
• 8 Space for second flash
There are typically four parts to a flash drive:
Standard-A USB plug – provides a physical
interface to the host computer.
USB mass storage controller – a small
microcontroller with a small amount of on-chip
ROM and RAM.
NAND flash memory chip(s) – stores data (NAND
flash is typically also used in digital cameras).
Crystal oscillator – produces the device's main
12 MHz clock signal and controls the device's
data output through a phase-locked loop.
The typical device may also include:
USB connector cover or cap
Some drives offer expandable storage via an internal
memory card slot, much like a memory card reader.[
LETS EXPLORE :-
USB Flash Drives or commonly called as Pen Drives are
popular removable storage media having a storage capacity
from 64 MB to 32 GB. They are preferred over the other conventional
storage devices like floppy disks or CD ROMs as they are faster
, smaller and have a longer life span.
1.A printed circuit board carrying the circuit elements and a USB
connector is shown in the above image.
2.The USB connector is protected by either retracting into the
body or by covering by a removable lid. There are two chips,
one is the USB controller and the other is the flash memory chip
The IC SK6211 shown in the above image is a controller which facilitates the data
communication between the PC/Laptop and the flash memory (EEPROM) of the
It is fully compatible with USB 2.0 protocols and USB Mass storage class V1.0
The devices like memory card, hard disk, pen drive etc with high data storage
capacity fall under the category of Mass Storage Devices.
The chip which is shown in the image above is a NAND type flash memory which has
fast read, write and erase cycles. The data is stored in memory cells of the EEPROM.
The storage capacity of this memory is 2GB. There is another similar chip with
storage capacity of 2GB on the other side of the PCB, thereby making the total
capacity of the pen drive to be 4GB.
The above image shows the other side of PCB. The second memory
chip, a crystal oscillator and a number of surface mount
components are soldered which are required for the operation of
the pen drive.
The crystal oscillator produces the clock signal for the
correct operation of the device. The crystal oscillator
used here runs at a clock frequency at 12 MHz.
Magnetic Tapes stores data sequentially, hence sequential accessing of data is
possible only, whereas in USB flash drive random accessing can be done.
Size of pen-drive is much smaller than floppy Disk(3.5 inch).
Not used in modern computers.
RW varieties up to about 1,000 erase/write cycles,
while modern NAND-based flash drives often last for
500,000 or more erase/write cycles.
They are slower than their flash-based counterparts
Standard 12 cm optical discs are larger than flash drives and more subject
Flash drives use little power, have no fragile
moving parts, and for most capacities are small and
Data stored on flash drives is impervious to
mechanical shock, magnetic fields, scratches and
Specially manufactured flash drives are available
that have a tough rubber or metal casing designed to
be waterproof and virtually "unbreakable". These
flash drives retain their memory after being
submerged in water, and even through a machine
Flash drives can sustain only a limited number of
write and erase cycles before the drive fails.
USB flash drives are more expensive per unit of
storage than large hard drives, but are less expensive
in capacities of a few tens of gigabytes as of 2011.