Flash Drives

Submitted by:

Animesh Shaw

Narula Institute of Technology

Content

INTRODUCTION WHAT IS COMPUTER MEMORY ?WHAT IS FLASH DRIVE ?HISTORYCOMPOSITIONDESIGN AND IMPLEMENTATIONESSENTIAL COMPONENTS ADDITIONAL COMPONENTSCOMPARISON WITH OTHER DRIVESUSES OF FLASH DRIVEADVANTAGESDISADVANTAGESFUTURE ENHANCEMENTS

INTRODUCTION

A flash memory combines a number of older technologies with the low cost ,low power consumption and small size which is possible by recent advance in microprocessors technology. These have a limited capacity and can be erased & overwritten for many number of times ,they do require complex high voltage drive circuitry.

What is Computer Memory?Computer data storage, often called storage or memory, refersto computer components, devices, and recording media thatretain digital data used for computing for some interval of time.Computer data storage provides one of the core functions of themodern computer, that of information retention. It is one of the fundamental components of all moderncomputers, and coupled with a central processing unit (CPU, aprocessor),implements the basic computer model used since the1940s.

Types Of StoragePrimary storage, presently known asmemory, is the only one directly accessibleto the CPU. The CPU continuously readsinstructions stored there and executesthem.Example..RAMSecondary storage, or storage in popularusage, differs from primary storage in that itis not directly accessible by the CPU.Example..Hard Disk, Flash Memory

Continue…Static Memory

A form of volatile memory similar to DRAM with the exception that it doesnot refresh on occasion.Dynamic Memory

A form of volatile memory which also requires the stored information to beperiodically re-read and re-written, or refreshed, otherwise it would vanish. Volatile Memory

Requires constant power to maintain the stored information. Since primarystorage is required to be very fast, it predominantly uses volatile memory.Non- Volatile Memory

Will retain the stored information even if it is not constantly supplied withelectric power. It is suitable for long-term storage of information.

What is Flash Memory ?Flash memory, sometimes called flash RAM, is a type ofsemiconductor device that combines important features of bothmemory & storage. These features include high-speed accessand retention of data in the absence of a power supply.Flash memory gets its name because the microchip is organizedso that a section of memory cells are erased in a single action or"flash."Flash memory refers to a particular type of EEPROM, orElectronically Erasable Programmable Read Only Memory. It is amemory chip that maintains stored information withoutrequiring a power source.

HISTORY

In 2000 IBM first start selling pen drives in collaborationwith TREK technology.The first Pen drive have the capacity of 8 MB.

COMPOSITION

•A flash drive consists of a small printed circuit board protected by a plastic body•A USB flash drive consists of a NAND-type flash memory data storage device•It consists of standard type- A USB connection allowing plugging in the port of personal computer

DESIGN & IMPLEMENTATION

One end of the device is fitted with a USB connectorIts chip consist of a printed board with power circuits andICs mounted on itIt typically use the USB mass storage device class tocommunicate with the host

ESSENTIAL COMPONENTSA USB connectorCrystal oscillator -controls device

data outputMass storage controller

containing microcontroller,RAM & ROM

NAND flash memory chip-usedfor storing data.

Mohd wasif (1 year,2nd semester)

ADDITIONAL COMPONENTS

Jumpers and test pins -for testing and loading codes intothe microprocessorLEDs -indicates data transferWrite protect switches -indicates whether the drive is in“write protection” modeUSB connector cap

How Flash Memory Works?

It has a grid of columns and rows with a cellthat has two transistors at each intersection.The two transistors are separated from eachother by a thin oxide layer. One of thetransistors is known as a floating gate, andthe other one is the control gate.The floating gate's only link to the row, orwordline, is through the control gate. Aslong as this link is in place, the cell has avalue of 1.To change the value to 0 requires a curiousprocess called Fowler-Nordheimtunneling.

Flash Memory: Tunneling and ErasingTunneling is used to alter the placement of electrons in thefloating gate. An electrical charge, usually 10 to 13 volts, isapplied to the floating gate. The charge comes from the column,or bitline, enters the floating gate and drains to a ground.This charge causes the floating-gate transistor to act like anelectron gun. The excited electrons are pushed through andtrapped on other side of the thin oxide layer, giving it a negativecharge.These negatively charged electrons act as a barrier between thecontrol gate and the floating gate.A special device called a cell sensor monitors the level of thecharge passing through the floating gate.

Continue…If the flow through the gate is above the 50 percent threshold, it has avalue of 1. When the charge passing through drops below the 50-percent threshold, the value changes to 0. A blank EEPROM has all ofthe gates fully open, giving each cell a value of 1.The electrons in the cells of a flash-memory chip can be returned tonormal ("1") by the application of an electric field, a higher-voltagecharge.Flash memory uses in-circuit wiring to apply the electric field eitherto the entire chip or to predetermined sections known as blocks. Thiserases the targeted area of the chip, which can then be rewritten.Memory works much faster than traditional EEPROMs becauseinstead of erasing one byte at a time, it erases a block or the entirechip, and then rewrites it.

Removable Flash Memory Cards

While your computer's BIOS chip is themost common form of Flash memory,removable solid-state storage devicesare also popular.SmartMedia and CompactFlash cardsare both well-known, especially as"electronic film" for digital cameras.Other removable flash-memoryproducts include Sony's Memory Stick,PCMCIA memory cards, and memorycards for video game systems.

Continue…As shown below, SmartMedia cardsare extremely simple. A planeelectrode is connected to the flash-memory chip by bonding wires.The flash-memory chip, planeelectrode and bonding wires areembedded in a resin using a techniquecalled over-molded thin package(OMTP).This allows everything to be integratedinto a single package without the needfor soldering.The OMTP module is glued to a basecard to create the actual card.

Comparison with other devices

FloppyOptical media(CD & DVD)TapeExternal hard disc

USES OF PEN DRIVE

Personal data transport.Booting operation system.Audio players.Music storage and marketing.

Advantage Of Flash MemoryThe advantages of flash memory as compared with HDDs

are substantial.

Smaller in size Light weightLow power consumptionLonger life expectancyGreatly improved shock resistance.

Disadvantage…The main disadvantage at present is that the cost per unit ofstorage capacity is still much higher than that for HDDs.

However, the gap is gradually narrowing.In contrast to RAM and like all types of EEPROMs, it wears outafter a certain number of write and erase cycles. This is due tothe degradation of the insulating oxide layer around themicroscopic cells that are used to store data. Fortunately,however, the number of cycles in most applications is sufficientlylow that this situation is not frequently encountered.Bad Blocks

ApplicationsFlash memory is very useful in a variety of applications including:

Your computer BIOSMemory CardsMp3 players Modems Video game cards Digital cellular phones Digital cameras